Modifying effect of prenatal care on the association between young maternal age and adverse birth outcomes

The objectives were to investigate the prevalence of adverse birth outcomes according to maternal age range in the city of Rio de Janeiro, Brazil, in 2002, and to evaluate the association between maternal age range and adverse birth outcomes using additive interaction to determine whether adequate prenatal care can attenuate the harmful effect of young age on pregnancy outcomes.

A cross-sectional analysis was performed in women up to 24 years of age who gave birth to live children in 2002 in the city of Rio de Janeiro. To evaluate adverse outcomes, the exposure variable was maternal age range, and the outcome variables were very preterm birth, low birth weight, prematurity, and low 5-minute Apgar score. The presence of interaction was investigated with the composite variable maternal age plus prenatal care. The proportions and respective 95% confidence intervals were calculated for adequate schooling, delivery in a public maternity hospital, and adequate prenatal care, and the outcomes according to maternal age range. The chi-square test was used. The association between age range and birth outcomes was evaluated with logistic models adjusted for schooling and type of hospital for each prenatal stratum and outcome. Attributable proportion was calculated in order to measure additive interaction.

Of the 40,111 live births in the sample, 1.9% corresponded to children of mothers from 10-14 years of age, 38% from 15-19 years, and 59.9% from 20-24 years. An association between maternal age and adverse outcomes was observed only in adolescent mothers with inadequate prenatal care, and significant additive interaction was observed between prenatal care and maternal age for all the outcomes.

Adolescent mothers and their newborns are exposed to greater risk of adverse outcomes when prenatal care fails to comply with current guidelines.