RESUMEN
OBJECTIVE: Pregnancy in adolescence is a global health issue, especially in developing countries. Additionally, the recommended gestational weight gain (GWG) is usually based on pre-pregnancy BMI and that might be complex for pregnant teens. The study objective was to compare three different methods of BMI classification and suggest the best way of determining pre-pregnancy BMI and monitoring GWG among pregnant adolescents. DESIGN: Pre-pregnancy weight, weight at first prenatal visit, height, sociodemographic, reproductive and perinatal data were collected. Weighted kappa and McNemar statistics were used to assess agreement between the classification methods. SETTING: Prof. Dr Jose Aristodemo Pinotti Women's Hospital, University of Campinas, Brazil.ParticipantsPrimiparas younger than 19 years of age and with less than 20 weeks of gestational age (n 150). RESULTS: BMI of the primiparas was determined according to the WHO recommendation for adult women, the Child Growth Standards (CGS) and their gynaecological age (GA). The WHO and GA measurements presented a strong agreement with each other (κ w=0·99; 95 % CI 0·97, 1·00), but did not agree with the CGS classification (κ w=0·62; 95 % CI 0·50, 0·74 by WHO; κ w=0·62; 95 % CI 0·51, 0·74 by GA). Also, inadequate GWG was observed in 72·2 % of cases and was correlated with a higher rate of caesarean birth. CONCLUSIONS: BMI classification according to the CGS differed from WHO and GA. However, CGS and WHO agreed on perinatal outcomes. We recommend using BMI classification by WHO to assess pregnant adolescents, since it is easily applied and better known among health professionals.