The objective of this review was to assess whether early age at first childbirth is associated with increased risk of poor pregnancy outcomes. Early age at childbirth is variously defined in studies of its effect on maternal and infant health. In this systematic review, we limit analysis to studies of at least moderate quality that examine first births among young mothers, where young maternal age is defined as low gynaecological age (≤2 years since menarche) or as a chronological age ≤16 years at conception or delivery. We conduct meta‐analyses for specific maternal or infant health outcomes when there are at least three moderate quality studies that define the exposure and outcome in a similar manner and provide odds ratios or risk ratios as their effect estimates. We conclude that the overall evidence of effect for very young maternal age (<15 years or <2 years post‐menarche) on infant outcomes is moderate; that is, future studies are likely to refine the estimate of effect or precision but not to change the conclusion. Evidence points to an impact of young maternal age on low birthweight and preterm birth, which may mediate other infant outcomes such as neonatal mortality. The evidence that young maternal age increases risk for maternal anaemia is also fairly strong, although information on other nutritional outcomes and maternal morbidity/mortality is less clear. Many of the differences observed among older teenagers with respect to infant outcomes may be because of socio‐economic or behavioural differences, although these may vary by country/setting. Future, high quality observational studies in low income settings are recommended in order to address the question of generalisability of evidence. In particular, studies in low income countries need to consider low gynaecological age, rather than simply chronological age, as an exposure. As well, country‐specific studies should measure the minimum age at which childbearing for teens has similar associations with health as childbearing for adults. This ‘tipping point’ may vary by the underlying physical and nutritional health of girls and young women.

Short inter-pregnancy intervals (IPIs) have been associated with adverse maternal and infant health outcomes in the literature. However, many studies in this area have been lacking in quality and appropriate control for confounders known to be associated with both short IPIs and poor outcomes. The objective of this systematic review was to assess this relationship using more rigorous criteria, based on GRADE (Grading of Recommendations Assessment, Development and Evaluation) methodology. We found too few higher-quality studies of the impact of IPIs (measured as the time between the birth of a previous child and conception of the next child) on maternal health to reach conclusions about maternal nutrition, morbidity or mortality. However, the evidence for infant effects justified meta-analyses. We found significant impacts of short IPIs for extreme preterm birth [<6 m adjusted odds ratio (aOR): 1.58 [95% confidence interval (CI) 1.40, 1.78], 6–11 m aOR: 1.23 [1.03, 1.46]], moderate preterm birth (<6 m aOR: 1.41 [1.20, 1.65], 6–11 m aOR: 1.09 [1.01, 1.18]), low birthweight (<6 m aOR: 1.44 [1.30, 1.61], 6–11 m aOR: 1.12 [1.08, 1.17]), stillbirth (aOR: 1.35 [1.07, 1.71] and early neonatal death (aOR: 1.29 [1.02, 1.64]) outcomes largely in high- and moderate-income countries. It is likely these effects would be greater in settings with poorer maternal health and nutrition. Future research in these settings is recommended. This is particularly important in developing countries, where often the pattern is to start childbearing at a young age, have all desired children quickly and then control fertility through permanent contraception, thereby contracting women's fertile years and potentially increasing their exposure to the ill effects of very short IPIs.

Women who see a medication on one of these 'safe' lists would be led to believe that there is no increased risk of birth defects resulting from exposure. Thus, women are being reassured that fetal exposure to these medications is safe even though a sufficient evidence base to determine the relative safety or risk does not exist.