Public Health Nutrition Editorial Highlight: ‘How to classify body mass index among pregnant adolescents? A prospective cohort’ Authors: Maira Pinho-Pompeu, Daiane Sofia Moraes Paulino, Sirlei Siani Morais, Marina Yumi Crubelatti, João Luiz Pinto e Silva and Fernanda Garanhani Surita discuss their research below.

Pregnancy in adolescence is a global health issue. Complications during pregnancy and childbirth are the main cause of death in adolescent girls, especially in developing countries. Nutritional diagnosis in early pregnancy and adequate orientation about Gestational Weight Gain (GWG) could prevent adverse perinatal outcomes. However, assessing the nutritional status of pregnant adolescents is challenging due to a lack of a specific nutritional guideline for this population. GWG recommendations were developed for adult women and are based on pre-pregnancy Body Mass Index (BMI).

In order to evaluate the best method of classifying pre-pregnancy BMI and monitoring GWG among pregnant adolescents, we compared different methods of BMI classification. For this purpose, we followed 150 primiparas younger than 19 years old (average age 15.4) from early pregnancy until childbirth, and the best method of BMI classification was chosen according to better perinatal outcomes.

These three most common BMI classifying methods were applied:

1. 1-World Health Organization (WHO) recommendation for adult women, divided into Underweight (BMI<18.5), Healthy Weight (BMI 18.5-24.9), Overweight (BMI 25.0-29.9) and Obesity (BMI≥30).
2. Child Growth Standards (CGS) BMI-for-age for girls between 5 to 19 years old, with z-scores classified into Severe Obesity, Obesity, Overweight, Healthy Weight, Wasted and Severely Wasted.
3. Gynecologic Age (GA), in which adolescents were divided into two groups, according to the years elapsed since menarche: girls with GA equal or older than three years were classified according to the WHO classification, and girls with GA less than three years were classified according to CGS.

This study showed a positive correlation between the BMI classification by WHO and GA for pregnant adolescents, but did not show an agreement between these classifications and the CGS classification. The BMI classifications by CGS differs from the other two classifications, WHO and GA, overestimating underweight female adolescents, and decreasing the proportion of overweight and obese ones. A high prevalence of overweight and obesity was observed in all three methods.

A high prevalence of overweight and obesity according with pre-pregnancy BMI was observed in all three methods of BMI classification (30.6% by CGS classification and 17.3% by WHO and GA Classification). In addition, an inadequate GWG was observed in 72.2% of the cases and was correlated with a higher rate of cesarean births.

In summary, the differences between the three methods of BMI classification can make it possible that the same pregnant adolescent receives different BMI classifications and consequently different GWG recommendations during prenatal care.

Therefore, we recommend BMI classification according to WHO standards for adult women to assess pregnant adolescents and determine optimal weight gain during pregnancy, especially as it is an easily applied guideline and widely known among health professionals.

The full article ‘How to classify body mass index among pregnant adolescents? A prospective cohort’ published in Public Health Nutrition is available to download for free until 31st January 2019.

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