Discussion
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In this study, babies born to adolescent mothers had poorer birth and neonatal outcomes as seen in baseline anthropometric measures and a higher risk of all-cause mortality by 6 months but similar growth outcomes at 6 months compared with those born to adult mothers.Similarly to findings of previous studies, babies born to adolescent mothers had lower weight, height, MUAC, LAZ, WAZ and WLZ at baseline and higher odds of mortality by 6 months.At 6 months, there were very small differences between babies born to adolescent and adult mothers in most anthropometric outcomes in fully adjusted models. This may be due to the smaller babies gaining weight more quickly. Previous studies show that there may be a faster weight-gain ‘catch-up growth’ among infants who are of low birthweight compared with those who are not.In sensitivity analysis restricting to first-born children to account for confounding by birth order, our results were mostly similar but attenuated in magnitude. Babies born to adolescent mothers had poorer birth outcomes and higher mortality but similar 6-month growth outcomes. This attenuation of effect may be partly explained by differences related to birth order. Studies show that independently of maternal age, a child’s birthweight increases with birth order.There was potential for selection bias in this study because neonates had to weigh >2500 g (be of sufficient weight) and be ≥8 days old (survive their first week of life) to be enrolled in the trial. If babies born to adolescent mothers more often died during the first week or were of lower weight, this could lead to differential selection into the study cohort. This would bias the results towards the null as a higher proportion of the well (survivors with higher weight) babies from adolescent mothers would be represented in the study. This is similar to our finding from the QBA in which the adjusted OR went further away from the null as the difference in the selection probability of adolescent and adult mothers with child mortality at 6 months increased from 0% to 5%, 10%, 15% and 20%. When considering the causal structure, this is similar to collider stratification in which we restrict the study to babies who survived their first week of life and are of sufficient weight, therefore opening the back-door path from maternal age to infant mortality (This study has some limitations. First, there were some missing values for 6-month anthropometric measures/outcomes (12–15%) and babies born to adolescent mothers were more likely to have missing outcomes (15.3% vs 11.5% of those born to adult mothers). However, estimates obtained from inverse probability of censoring weighting for growth outcomes were very similar to complete case analysis from unweighted analyses (