Abstracts

INTRODUCTION

Epidemiological studies show that the inadequacy of the anthropometric state of women, before and during pregnancy, constitutes a public health problem by promoting the development of gestational intercurrences and influencing their health conditions in the postpartum and conceptus periods¹1. Padilha PC, Accioly E, Veiga GV, Bessa TC, Líbera BD, Nogueira JL, et al. The performance of various anthropometric assessment methods for predicting low birth weight in pregnant women. Rev Bras Saude Mater Infant 2009; 9(2):197-206. ^{, 2}2. Choi SK, Park IY, Shin JC. The effects of pre-pregnancy body mass index and gestational weight gain on perinatal outcomes in Korean women: a retrospective cohort study. Reprod Biol Endocrinol 2011; 9: 6..

Developing countries have been showing distinct situations of nutritional deviation problems: a decline in malnutrition and an increase in overweight, obesity and chronic diseases³3. Batista-Filho M, Rissin A. A transição nutricional no Brasil: tendências regionais e temporais. Cad Saúde Pública 2003; 19(suppl1): S181-91.

4. Padilha PC, Saunders C, Machado RCM, Silva CL, Bull A, Sally EOF, et al. Associação entre o estado nutricional pré-gestacional e a predição do risco de intercorrências gestacionais. Rev Bras Saude Mater Infant 2007; 29(10): 511-8. ^{- 5}5. Brasil. Ministério da Saúde. Indicadores de Vigilância Alimentar e Nutricional: Brasil 2006. Brasília: Ministério da Saúde; 2009.. Brazil, in especial, is going through a phase of epidemiological transition, characterized by the change in populational morbidity profile, in which infectious and parasitic diseases give place to nontransmissible chronic diseases, such as obesity³3. Batista-Filho M, Rissin A. A transição nutricional no Brasil: tendências regionais e temporais. Cad Saúde Pública 2003; 19(suppl1): S181-91.. According to data from the Pesquisa de Orçamentos Familiares (2008 - 2009), the use of a BMI-for-age anthropometric index, the weight deficit in adolescent girls and grown women was 3.0 and 3.6%, respectively. The excess of weight in adult women was 48% and, in adolescent girls, 19.4%. Obesity, in turn, was observed in 16.9% of adult women and in 4.0% of adolescent young women6. Given the increased risk of prematurity and maternal mortality in situations of low gestational weight and the association of obesity to a higher rate of diabetes, hypertensive syndromes in pregnancy, birth sequelae and cesarean sections, the nutritional diagnosis of the pregnant woman and the recommendation weight gain are essential in order to ensure a positive obstetric outcome⁷7. Brasil. Ministério da Saúde. Atenção ao pré-natal de baixo risco. Brasília: Ministério da Saúde; 2012. ^{, 8}8. American Dietetic Association; American Society of Nutrition, Siega-Riz AM, King JC. Position of the American Dietetic Association and American Society for Nutrition: obesity, reproduction, and pregnancy outcomes. J Am Diet Assoc 2009; 109(5): 918-27..

International standards of weight gain recommendations have been used and reviewed over the last 50 years, showing the relevance of choosing the most adequate method for maternal anthropometric evaluations in clinical practice⁹9. Ghosh A. Anthropometric and body composition characteristics during pregnancy: a study from West Bengal India. HOMO 2012; 63(3): 233-40.

10. Melo MIB, Souza AI, Figueiroa AN, Cabral-Filho JE, Benício MHD, Batista-Filho M. Estado nutricional de gestantes avaliado por três diferentes métodos de classificação antropométrica. Rev Nutr 2011; 24(4): 585-92.

11. Deierlein AL, Siega-Riz AM, Adair LS, Herring AH. Effects of pre-pregnancy body mass index and gestational weight gain on infant anthropometric outcomes. J Pediatr 2011; 158(2): 221-6. ^{- 12}12. Atalah E, Castillo C, Castro R, Aldea A. Propuesta de un nuevo estándar de evaluación nutricional en embarazadas. Rev Med Chile 1997; 125: 1429-36..

In 2009¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009., the Institute of Medicine (IOM) issued new recommendations for weight gain during pregnancy, based on the pre-gestational body mass index (BMI), based on the proposal originally published in 1990¹⁴14. Institute of Medicine. Nutrition during pregnancy. Washington: National Academy Press; 1990. and reviewed in 1992¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992.. It is noteworthy that, for the adolescents, the IOM committee kept the same nutritional evaluation procedure suggested for the adults, by lack of scientific evidence that support the differentiated adoption of adequacy of weight gain for teenagers¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009.

14. Institute of Medicine. Nutrition during pregnancy. Washington: National Academy Press; 1990. ^{- 15}15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992..

In Brazil, in the most recent guidelines of the Ministry of Health (MOH) for prenatal low-risk⁷7. Brasil. Ministério da Saúde. Atenção ao pré-natal de baixo risco. Brasília: Ministério da Saúde; 2012., the procedures recommended for the anthropometric and planning evaluation of gestational weight gain suggested for the grown ups were kept for the adolescents, without contemplating their specificities¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. ^{, 14}14. Institute of Medicine. Nutrition during pregnancy. Washington: National Academy Press; 1990..

In 2007, the World Health Organization (WHO)¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... proposed the adoption of a new reference for the nutritional diagnosis of adolescents, based on the BMI, replacing the recommendations of the WHO in 1995¹⁷, enabling the classification of adolescents according to an age appropriate (in years and months) reference. It was then possible to better reflect on the weight and height profile of the teenagers and the highest comparability between populations. However, this recommendation was not incorporated by the MOH⁷7. Brasil. Ministério da Saúde. Atenção ao pré-natal de baixo risco. Brasília: Ministério da Saúde; 2012. ^{, 18}18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. in the nutritional evaluation of pregnant teenagers, being used only for the non-pregnant ones¹⁹19. Brasil. Ministério da Saúde. Protocolos do Sistema de Vigilância Alimentar e Nutricional - SISVAN na assistência à saúde. Brasília: Ministério da Saúde; 2008..

Therefore, the proposals published so far by the international and national health committees for pregnant adolescents are still based on the recommendations proposed for pregnant adults. The reason for this classification has been based on the hypothesis that the adolescents would benefit from a higher weight gain program, at the expense of misclassifications such as low weight in the beginning of pregnancy⁷7. Brasil. Ministério da Saúde. Atenção ao pré-natal de baixo risco. Brasília: Ministério da Saúde; 2012. ^{, 13}13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009.. On the other hand, studies indicate that gestational weight gain above what is recommended may be associated to future unwanted outcomes in the adult life of these pregnant teenagers, among them the retention of weight after labor, with consequences to the development of obesity associated diseases²⁰20. Drehmer M, Duncan BB, Kac G, Schmidt MI. Association of second and third trimester weight gain in pregnancy with maternal and fetal outcomes. PLoS One 2013; 8(1): e54704.. In addition to the above, the most used recommendations for weight gain planning during pregnancy⁷7. Brasil. Ministério da Saúde. Atenção ao pré-natal de baixo risco. Brasília: Ministério da Saúde; 2012. ^{, 13}13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. ^{, 18}18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. were not validated according to the prenatal results of adolescent.

Thus, the investigation on the best gestational anthropometric evaluation method, especially in teenagers, needs to be encouraged, and the topic should be discussed by researchers and professionals in the evaluation of prenatal care quality¹1. Padilha PC, Accioly E, Veiga GV, Bessa TC, Líbera BD, Nogueira JL, et al. The performance of various anthropometric assessment methods for predicting low birth weight in pregnant women. Rev Bras Saude Mater Infant 2009; 9(2):197-206.. These methods are expected to present good sensitivity and specificity to classify, appropriately, the maternal nutritional status and to identify the risk situations for an unwanted obstetric outcome in pregnant adolescents¹⁷17. World Health Organization. Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: World Health Organization; 1995..

Given the above, this study intends to evaluate the performance of different methods of gestational anthropometric evaluation in a sample of pregnant teenagers in the city of Rio de Janeiro, in order to assess their predictive ability as to the prenatal outcome of birth weight inadequacy.

METHODS

The work is part of the "Estudo da Morbi-mortalidade e da Atenção Peri e Neonatal no município do Rio de Janeiro, 1999-2001" and was developed based on a sample of 10,072 postpartum women who were hospitalized in maternities of this municipality for the labor process, between July 1999 and March 2001. It is a cross-sectional study, and further methodological details are described by Leal et al.²¹21. Leal MC, Gama SGN, Campos MR, Cavalini LT, Garbayo LS, Porto Brasil CL, et al. Fatores associados à morbimortalidade perinatal em uma amostra de maternidades públicas e privadas do Município do Rio de Janeiro, 1999-2001. Cad Saúde Pública 2004; 20(S1): 20-33.. Out of the total sample, 19.6% of the mothers were teenagers, according to the WHO classification¹⁷17. World Health Organization. Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: World Health Organization; 1995., which resulted in a total of 1,968 mothers, though none of them was under 12 years of age. For this study, 826 new adolescent moms were selected, according to the following inclusion criteria: to have weight (before pregnancy and at the end of it), height and gestational age at the moment of birth information according to the date of the last menstrual period (LMP); to have no chronic disease; to have a single-fetus pregnancy.

In the intention of controlling possible selection bias, this study used a comparative analysis of the socio-demographic variables, health and obstetric results between the group of selected adolescent mothers and the ones who did not meet the inclusion criteria. However, no significant differences were found regarding the obstetric results²²22. Barros DC. Avaliação do estado nutricional antropométrico de gestantes adolescentes no Município do Rio de Janeiro [tese de doutorado]. Rio de Janeiro: Escola Nacional de Saúde Pública Sergio Arouca da Fundação Oswaldo Cruz; 2009..

The data collected from both mother's and newborn's medical records, in addition to interviews with the mothers immediately after labor, by Grant students of nursery and medicine, appropriately trained and supervised by the coordinators.

In order to evaluate the anthropometric nutritional status, there were used information regarding weight before and at the end of pregnancy and height self-reported by the teenagers at the moment of the interview. The use of self-reported data has been recommended in conducting large populational studies²³23. Farias Jr JC. Validade das medidas auto-referidas de peso e estatura para o diagnóstico do estado nutricional de adolescentes. Rev Bras Saúde Matern Infant 2007; 7(2): 167-74. ^{, 24}24. Thomaz PMD, Silva EF, Costa THM. Validade de peso, altura e índice de massa corporal autorreferidos na população adulta de Brasília. Rev Bras Epidemiol 2013; 16(1): 157-69.; however, in this study, these were validated during field work of the original project²⁵25. Oliveira AF, Gadelha AMJ, Leal MC. Estudo da validação das informações de peso e estatura em gestantes atendidas em maternidades municipais no Rio de Janeiro, Brasil. Cad Saúde Pública 2004; 20(supl.1): 92-100.. For the classification of the pre-gestational nutritional status, according to the BMI, the cutoff points and the classification recommended by the committees: IOM¹⁴14. Institute of Medicine. Nutrition during pregnancy. Washington: National Academy Press; 1990. ^{, 15}15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. and WHO¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... , were used, being this last one with the Z score adapted classification proposed for the food and nutritional surveillance in Brazil¹⁹19. Brasil. Ministério da Saúde. Protocolos do Sistema de Vigilância Alimentar e Nutricional - SISVAN na assistência à saúde. Brasília: Ministério da Saúde; 2008..

For the evaluation of adequacy of total gestational weight gain, after the classification of the pre-pregnancy BMI by the different methods, the total gain weight of the pregnant adolescent (final weight - pre-pregnancy weight) with a gestational weight gain recommended for each case, envisaged by the IOM¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. ^{, 15}15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. and the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006., were compared. In the implementation of the recommendation by the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006., it was adopted the BMI pre-pregnancy classification recommended by the WHO¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... , adapted to Brasil¹⁹19. Brasil. Ministério da Saúde. Protocolos do Sistema de Vigilância Alimentar e Nutricional - SISVAN na assistência à saúde. Brasília: Ministério da Saúde; 2008.. It was also considered the cutoff point of 3 percent for the definition of low height and, in those cases, it was considered the lower limit of recommended weight gain for each pre-pregnancy BMI category as the appropriate total weight gain.

The remaining variables selected for the analysis were: maternal age, years of school education, menarcheal age, number of prenatal medical care visits, type of baby delivery and birth weight. Birth weight was classified in low, adequate and macrosomia. There were considered to be low weighted those with less than 2,500 g; adequate, with 3,999 g and macrosomic, equal or higher than 4, 000 g¹⁷17. World Health Organization. Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: World Health Organization; 1995..

The agreement between the pre-pregnancy BMI classification proposed by the WHO16 and by the IOM¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. was verified through the Kappa (k) statistic. The proposal of BMI values by the WHO¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... and the BMI classification according to the Z scores for teenagers in years of age recommended by the MOH¹⁹19. Brasil. Ministério da Saúde. Protocolos do Sistema de Vigilância Alimentar e Nutricional - SISVAN na assistência à saúde. Brasília: Ministério da Saúde; 2008. was considered as the gold standard in this study. In the concordance analysis, it was considered bad when k = 0; weak k = 0.01 - 0.20; poor k = 0.21 - 0.40; regular k = 0.41 - 0.60; good k = 0.61 - 0.80; great k = 0.81 - 1.0026.

In the statistical analysis, the average and the standard deviation of the continuous variables were calculated, estimating the odds ratio (OR) among the exposure and disclosure factors - birth weight, with a confidence interval of 95% (95%CI).

In the multivariate analysis, it was used the multinomial logistic regression, stepwise method, with the calculation of raw and adjusted ORs and95%CI, in order to identify the predicting variables of the outcomes of interest and the association with the diagnostic of gestational weight adequacy, obtained according to the different methodologies tested in the study. The inclusion criterion of the variables in the model was p < 0.05 and, for exclusion, p > 0.10. In order to study the performance of the methods of gestational weight gain adequacy in predicting low birth weight and macrosomia, the values of sensitivity (Se), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV) and accuracy were calculated.

The Project was approved by the Research Ethics Committee of the Fundação Oswaldo Cruz (FIOCRUZ), approval No 23, of 11/08/1999, and a Informed Consent was signed by the new mothers or, if necessary, by the guardians responsible for the teenagers, after agreeing to take part in this research. The analysis were made by the Statistical Package for the Social Sciences (SPSS) software for Windows, v. 17.0.

RESULTS

The 826 adolescent mothers interviewed were, on average, 17.6 years old (standard deviation - SD = 1.35), 7.7 years of school education (SD = 2.33) and 7.2 Medical consultations for prenatal care (SD = 2.00). The coverage of prenatal care was 97.9%, with around 57.5% of them made 7 or more visits during pregnancy. The average birth weight was 3,113 g (SD = 613), the LBW prevalence was 10.8% and the macrosomia was 4.0%. The average gestational age at the time of birth was 38.5 weeks, considering 13% of the total were born before completing 37 weeks.

In Table 1, it is observed that birth weight was associated with adequate gestational weight gain regardless the anthropometric evaluation method adopted in the study. In relation to the sociodemographic, anthropometric, prenatal care and gestational outcomes variables, these were not associated with birth weight.

Table 2 presents the concordance of the pre-pregnancy anthropometric nutritional status classification according to the recommendation of the WHO¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... , in relation to the recommendations by the IOM¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. ^{, 15}15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. for adolescent mothers. The results show a better agreement between the classification by the WHO¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... and the one by the IOM (2009)¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. (k = 0.80; 95%CI 0.74 - 0.86). When compared to the IOM (1992)¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992., it was observed a lack of concordance for all classes, showing that 40% of the teenagers were classified in different categories, a result confirmed by the low kappa value found, even after being adjusted (k = 0.47; 95%CI 0.40 - 0.54).

In Table 3, the values of Se, Sp, PPV and NPV values and the accuracy of the appropriate evaluation method for gestational weight gain in relation to the child's weight at the time of birth are presented. In order to identify the LBW, the Se varied from 61.6 (MS, 2006)¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. to 68.6%¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992.; the Sp, from 69.5¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. to 66.4%¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. and the better accuracy values were obtained with the methods proposed by the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. and the IOM (2009)¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009.. As opposed to that, for the identification of macrosomy, the Se varied from 29.918 to 25.4%¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992.; the Sp, from 31.3¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. to 50.0%¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992., and the best accuracy value were obtained through the method proposed by the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006..

Table 4 shows simple and complex logistic regressions for the three adequacy models for gestational weight gain and other independent variables with explanatory potential for outcomes - low birth weight and macrosomia.

It is observed that the adequacy of gestational weight gain through the method proposed by the IOM¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. presented a higher prediction for LBW (raw OR = 3.84; 95%CI 2.19 - 6.74), according to the method proposed by the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. (raw OR = 2.88; 95%CI 1.73 - 4.79), among the adolescents who presented gestational weight gain below the recommendation. The pregnant adolescent who gained weight below the recommendation and attended to six or more medical prenatal consultations had lower chance of having low birth weight babies.

In the prediction of macrosomia, the appropriate gestational weight gain method proposed by the MOH18 presented a better performance among the adolescents with gestational weight gain above the recommendation (adjusted OR = 2.37; 95%IC 1.03 - 6.80), in relation to other methods. The pregnant teenagers who gained more weight than recommended and with more than six years of school education had a smaller chance of having newborns with macrosomia.

DISCUSSION

The study shows that adolescent mothers present good sociodemographic, anthropometric and prenatal care conditions, with averages close to satisfactory for the populations in general¹⁷17. World Health Organization. Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: World Health Organization; 1995. ^{, 27}27. Brasil. Ministério da Saúde. Pesquisa Nacional de Demografia e Saúde da Criança e da Mulher 2006. Brasília: Ministério da Saúde; 2008..

The number of prenatal medical care exceeded the minimum recommended¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. and the average age of the adolescent mother was, favorably, closer to adulthood. However, data from the original research, not exposed in this article, show that, despite the broad prenatal care coverage among the interviewed mothers, the younger adolescents had fewer medical consultations and later care beginning²⁸28. Viellas EF, Gama SGN, Theme Filha MM, Leal MC. Gravidez recorrente na adolescência e os desfechos negativos no recém-nascido. Rev Bras Epidemiol 2012; 15(3): 443-54.. The most immature teenagers, both chronologically and biologically, have also shown lower weight gain and higher incidence of unwanted outcomes, such as premature birth and low birth weight²⁹29. Nielsen JN, Gittelsohn J, Anliker J, O'Brien K. Interventions to improve diet and weight gain among pregnant adolescents and recommedations for future research. J Am Diet Assoc 2006; 106(11): 1825-40..

In this study, considering the application of methods, proper of pre-pregnancy diagnosis of adults and adolescents in the adequacy of gestational weight gain, according to what was proposed by the IOM¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. ^{, 15}15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. and the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006., it was verified that all of them were significantly associated to the birth weight outcome.

In the comparison of the adopted classifications for the pre-pregnancy anthropometric nutritional diagnosis, the results of this study revealed that the recommendation by the WHO¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... presented a discrepancy of 40% in relation to the one by the IOM¹⁵. The discrepancy would be explained by the smaller proportion of adolescents classified as low weight and a higher proportion with adequate weight or overweight, according to what was proposed by the WHO¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... . Besides that, it was verified that, when applying the proposal by the IOM¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992., there was a higher proportion of adolescents with pre-pregnancy low weight BMI (< 19.8 kg/m²2. Choi SK, Park IY, Shin JC. The effects of pre-pregnancy body mass index and gestational weight gain on perinatal outcomes in Korean women: a retrospective cohort study. Reprod Biol Endocrinol 2011; 9: 6.), once this cutoff point was defined based on data of the adult American population.

With the same recommendation from the IOM¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009., this discrepancy is reduced to 5%, being considered as more adequate. Despite that, the adjustments proposed by the IOM are still not ideal for pregnant teenagers, since the cutoff points for the pre-pregnancy BMI classification are adopted by the WHO¹⁷ for grow ups. The discrepancy between the different methods applied ratifies the need of choosing the one which uses adequate cutoff points for adolescents³⁰30. National Research Council; Institute of Medicine. Influence of pregnancy weight on maternal and child health: workshop report. Washington: National Academy Press; 2007.

31. Groth S. Are the Institute of Medicine Recommendations for Gestational Weight Gain appropriate for adolescents? JOGNN 2007; 36(1): 21-7. ^{- 32}32. Fernandez ID, Olson CM, Dye TDV. Discordance in the assessment of pre-pregnancy nutritional status of adolescents: a comparison between the CDC and prevention sex- and age-specific BMI classification and the IOM-Based Classification Used for Maternal Weight-Gain Guidelines. J Am Diet Assoc 2008;108(6): 998-1002..

In the last few years, an increasing number of studies have been developed in order to guide the choice of anthropometric nutritional evaluation for pregnant women, particularly concerning the cutoff points adopted for the initial nutritional assessment, especially for teenagers³⁰30. National Research Council; Institute of Medicine. Influence of pregnancy weight on maternal and child health: workshop report. Washington: National Academy Press; 2007.

31. Groth S. Are the Institute of Medicine Recommendations for Gestational Weight Gain appropriate for adolescents? JOGNN 2007; 36(1): 21-7.

32. Fernandez ID, Olson CM, Dye TDV. Discordance in the assessment of pre-pregnancy nutritional status of adolescents: a comparison between the CDC and prevention sex- and age-specific BMI classification and the IOM-Based Classification Used for Maternal Weight-Gain Guidelines. J Am Diet Assoc 2008;108(6): 998-1002. ^{- 33}33. Benjumea MV. Exactitud diagnóstica de cinco referencias gestacionales para predecir el peso insuficiente al nacer. Biomédica 2007; 27: 42-55.. The choice of the method to be adopted must be accurate enough to guide the best gestational weight gain range³²32. Fernandez ID, Olson CM, Dye TDV. Discordance in the assessment of pre-pregnancy nutritional status of adolescents: a comparison between the CDC and prevention sex- and age-specific BMI classification and the IOM-Based Classification Used for Maternal Weight-Gain Guidelines. J Am Diet Assoc 2008;108(6): 998-1002.. The appropriate pre-pregnancy diagnosis ensures a healthy weight gain, with favorable impacts in the maternal outcome and in the future life of both mother and child³⁰30. National Research Council; Institute of Medicine. Influence of pregnancy weight on maternal and child health: workshop report. Washington: National Academy Press; 2007. ^{, 34}34. Nucci LB, Duncan BB, Mengue SS, Branchtein L, Schmidt MI, Fleck ET. Assessment of weight gain during pregnancy in general prenatal care services in Brazil. Cad Saúde Pública 2001; 17(6): 1367-74. ^{, 35}35. Padilha PC. Contribuições teórico-práticas para a assistência nutricional pré-natal [tese de doutorado]. Rio de Janeiro: Instituto de Nutrição Josué de Castro da Universidade Federal do Rio de Janeiro; 2011..

The gestational weight gain adequacy, proposed by the IOM¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. was the one which presented best Se in predicting LBW. On the other hand, in order to predict macrosomia, the proposal by the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006., which considered the pre-pregnancy nutritional diagnosis according to the WHO¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... criteria, proved to be the best option.

The Se, the Sp and the PPV depend on the association between a risk factor and determined result¹⁷17. World Health Organization. Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: World Health Organization; 1995.. In the prediction of LBW, the low values of Se for the adaptations of the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. and of the IOM (2009)¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. for weight gain adequacy, in relation to the adequacy of the IOM (1992)¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992., may be justified by the fact that the indicators were built from data obtained in studies with adult women.

Groth³¹31. Groth S. Are the Institute of Medicine Recommendations for Gestational Weight Gain appropriate for adolescents? JOGNN 2007; 36(1): 21-7. highlights two matters which differentiate the BMI categories in adult and adolescent pregnant women: (1) the BMI variation in adolescents depends on their age; and (2) there are different cutoff points for low and adequate weight, overweight and obesity. These differences may lead the professional into classifying the same adolescent as low weighted in the beginning of the pregnancy, by the proposal of IOM (1992)¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. and as adequate weight by the proposal of the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006., affecting, thus, the also differentiated application of weight gain range during pregnancy.

The low predictive values found for LBW may be attributed to the low prevalence of outcome and justified by the recognized interference that the prevalence of an event has on the PPV result²⁶26. Pereira MG. Epidemiologia: teoria e prática. Rio de Janeiro: Guanabara-Koogan; 2005.. On the other hand, the accuracy results were satisfactory for the LBW, making rather acceptable the effect of both possible positive and negative classifications in the analysis. In order for an indicator to be good, it is desirable that it has a high predictive ability and a narrow confidence interval, to be appropriate, sensible and specific for screening, in addition to being efficient, with low number of false classifications²⁶26. Pereira MG. Epidemiologia: teoria e prática. Rio de Janeiro: Guanabara-Koogan; 2005..

The recommendation with the best statistical performance in order to explain low birth weight was the proposed adequacy of weight gain by the IOM (1992)¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992., a result which may seem controversial and, at the same time, may indicate it as the best recommendation. The best sensibility of this method allows the identification of a greater proportion of pregnant teenagers in the low pre-pregnancy weight category, with higher chance of becoming mothers of LBW newborns. However, this ability has to be counterbalanced by the method to classifying those with adequate weight or overweight.

One may assume that, as a greater proportion of pregnant teenagers was classified with low weight pre-pregnancy BMI, the statistical results obtained when applying the method of the IOM (1992)¹⁵15. Institute of Medicine. Nutrition during pregnancy and lactation: an implementation guide. Washington: National Academy Press; 1992. may bring a false interpretation of the method in increasing the chance of identifying LBW risk. At the same time, it is observed that it does not identify the risk of overweight, with consequences for future macrosomic babies and postpartum weight retention and obesity of the mother³⁰30. National Research Council; Institute of Medicine. Influence of pregnancy weight on maternal and child health: workshop report. Washington: National Academy Press; 2007. ^{, 33}33. Benjumea MV. Exactitud diagnóstica de cinco referencias gestacionales para predecir el peso insuficiente al nacer. Biomédica 2007; 27: 42-55..

As opposed to that, the MOH recommendations¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. showed a greater chance of identifying future newborns with macrosomia, especially for new mothers with less than one year of school education.

Given the current nutritional situation, this result suggests that these may be useful, with contribution potential as for reducing cases of postpartum weight retention and obesity, events which present a rapid growth over the past recent times, particularly in younger and socially underprivileged classes²⁷27. Brasil. Ministério da Saúde. Pesquisa Nacional de Demografia e Saúde da Criança e da Mulher 2006. Brasília: Ministério da Saúde; 2008. ^{, 30}30. National Research Council; Institute of Medicine. Influence of pregnancy weight on maternal and child health: workshop report. Washington: National Academy Press; 2007..

In a recent study³⁵35. Padilha PC. Contribuições teórico-práticas para a assistência nutricional pré-natal [tese de doutorado]. Rio de Janeiro: Instituto de Nutrição Josué de Castro da Universidade Federal do Rio de Janeiro; 2011., the method of the IOM (2009)¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. presented better specificity ADN sensitivity for the outcomes most related to insufficient weight gain (low birth weight and small for gestational age newborns - SGA) in grown women. The results also indicate the need for further investigation regarding the ranges of weight gain proposed by the IOM (2009)¹³, for age groups, and its applicability for pregnant adolescents, especially Brazilian ones.

Finally, it is recognized that the pre-pregnancy nutritional status, according to the BMI values, interferes with gestational weight gain, with consequences to the obstetric outcome³³33. Benjumea MV. Exactitud diagnóstica de cinco referencias gestacionales para predecir el peso insuficiente al nacer. Biomédica 2007; 27: 42-55.. Therefore, the judicious choice of a method for such an assessment is essential for the definition of gestational weight gain ranges, aimed at improving birth weight.

It is noteworthy that, from the total of adolescent mothers interviewed in the original study, about 42% of them meet the inclusion criteria of possessing anthropometric information. Thus, it is assumed that the association between the anthropometric variables - pre-pregnancy BMI and weight gain - and the occurrence of adverse outcomes evidence in the study could have been potentialized if the anthropometric information of all the interviewed adolescent mothers were available.

However, a comparative analysis of the groups revealed significant differences, showing that the lack of anthropometric information was higher in adolescent pregnant women with worse sociodemographic and health conditions and obstetric results²⁴24. Thomaz PMD, Silva EF, Costa THM. Validade de peso, altura e índice de massa corporal autorreferidos na população adulta de Brasília. Rev Bras Epidemiol 2013; 16(1): 157-69.. Given this, the difference between the groups was controlled in multinomial logistic regression, in an attempt of minimizing the effect of possible selection bias.

Thus, as the poverty conditions of the adolescent mothers in this study associated to the weight gain above the expected, and not with lower gain, one may assume that the presence of the ones who did not have their anthropometric information could strengthen the choice of the method recommended by the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006., which considers the pre-pregnancy BMI classification by the¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... .

It is noteworthy that the study reflects the anthropometric profile of Brazilian pregnant adolescents, and the scientific production in this Field is still scarce in both national and international studies. Also noteworthy is the importance of the sampling universe studied, despite the losses, and the scientific findings which may support the reflection on the choice of method to be used in clinical practice of pregnant adolescents' prenatal care.

It is worth being stressed that, up to this date, there is no reference proposal based on national studies and validated for use with Brazilian pregnant adolescent prenatal care. Thus, the validation and performance studies of the proposed methods with international data are of great value.

The early identification of the inadequate pregnant nutritional status contributes to timely interventions during pregnancy, reflecting on the birth conditions of the child, especially among pregnant adolescents²²22. Barros DC. Avaliação do estado nutricional antropométrico de gestantes adolescentes no Município do Rio de Janeiro [tese de doutorado]. Rio de Janeiro: Escola Nacional de Saúde Pública Sergio Arouca da Fundação Oswaldo Cruz; 2009.. Studies which were devoted to the nutritional assessment indicated decrease in mortality rates and preterm births, as well as macrosomic prevention and weight retention after birth labor, being these last two considered a risk to future occurrence of cardiovascular diseases³⁰30. National Research Council; Institute of Medicine. Influence of pregnancy weight on maternal and child health: workshop report. Washington: National Academy Press; 2007. ^{, 35}35. Padilha PC. Contribuições teórico-práticas para a assistência nutricional pré-natal [tese de doutorado]. Rio de Janeiro: Instituto de Nutrição Josué de Castro da Universidade Federal do Rio de Janeiro; 2011..

CONCLUSION

The study demonstrated that the choice of specific methods for adolescent in determining their pre-pregnancy anthropometric nutritional assessment, as proposed by the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006., which considers the pre-pregnancy nutritional diagnosis according to the WHO criteria¹⁶16. World Health Organization. WHO reference 2007: growth reference data for 5-19 years. Disponível em http://www.who.int/growthref/en/2007 (Acessado em 18 setembro de 2008).
http://www.who.int/growthref/en/2007... , seems to be an adequate option for the current nutritional situation of Brazilian pregnant women. Besides that, the proposal by the MOH¹⁸18. Brasil. Ministério da Saúde. Pré-natal e puerpério: atenção qualificada e humanizada - manual técnico. Brasília: Ministério da Saúde; 2006. overcomes the one by the IOM (2009)¹³13. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington: National Academy Press; 2009. in rick identification for the birth of macrosomic children among adolescent, ensuring, at the same time, the identification of those with risk of low birth weight, adapting its use to the outcome we intend to prevent. Either way, it is worth mentioning the importance of investments in national research focused on the definition of population-specific methods, based on the pregnant Brazilian adolescent anthropometric data for clinical practice.

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