Maternal age and offspring developmental vulnerability at age five: A population-based cohort study of Australian children

Abstract

Background: In recent decades, there has been a shift to later childbearing in high-income countries. There is limited large-scale evidence of the relationship between maternal age and child outcomes beyond the perinatal period. The objective of this study is to quantify a child's risk of developmental vulnerability at age five, according to their mother's age at childbirth.

Methods and findings: Linkage of population-level perinatal, hospital, and birth registration datasets to data from the Australian Early Development Census (AEDC) and school enrolments in Australia's most populous state, New South Wales (NSW), enabled us to follow a cohort of 99,530 children from birth to their first year of school in 2009 or 2012. The study outcome was teacher-reported child development on five domains measured by the AEDC, including physical health and well-being, emotional maturity, social competence, language and cognitive skills, and communication skills and general knowledge. Developmental vulnerability was defined as domain scores below the 2009 AEDC 10th percentile cut point. The mean maternal age at childbirth was 29.6 years (standard deviation [SD], 5.7), with 4,382 children (4.4%) born to mothers aged <20 years and 20,026 children (20.1%) born to mothers aged ≥35 years. The proportion vulnerable on ≥1 domains was 21% overall and followed a reverse J-shaped distribution according to maternal age: it was highest in children born to mothers aged ≤15 years, at 40% (95% CI, 32-49), and was lowest in children born to mothers aged between 30 years and ≤35 years, at 17%-18%. For maternal ages 36 years to ≥45 years, the proportion vulnerable on ≥1 domains increased to 17%-24%. Adjustment for sociodemographic characteristics significantly attenuated vulnerability risk in children born to younger mothers, while adjustment for potentially modifiable factors, such as antenatal visits, had little additional impact across all ages. Although the multi-agency linkage yielded a broad range of sociodemographic, perinatal, health, and developmental variables at the child's birth and school entry, the study was necessarily limited to variables available in the source data, which were mostly recorded for administrative purposes.

Conclusions: Increasing maternal age was associated with a lesser risk of developmental vulnerability for children born to mothers aged 15 years to about 30 years. In contrast, increasing maternal age beyond 35 years was generally associated with increasing vulnerability, broadly equivalent to the risk for children born to mothers in their early twenties, which is highly relevant in the international context of later childbearing. That socioeconomic disadvantage explained approximately half of the increased risk of developmental vulnerability associated with younger motherhood suggests there may be scope to improve population-level child development through policies and programs that support disadvantaged mothers and children.

Fig 1. The distribution of maternal age at childbirth for children in the study population, overlaid with the proportion of children who were developmentally vulnerable on each outcome, by maternal age at childbirth.

Light grey columns, study population birth distribution by year of maternal age at childbirth; black point estimates with 95% CIs, proportion of children developmentally vulnerable on each outcome (specified in figure subtitle).

Fig 2. The absolute risk of developmental vulnerability on the physical health and well-being, social competence, and emotional maturity domains of the AEDC for every year of maternal age at childbirth between 15 and 45 years.

Model 1 includes adjustment for the child’s age at school entry, sex, and AEDC year; in addition to the covariates included in Model 1, Model 2 adjusts for private health insurance/patient status, mother born in Australia/overseas, mother partnered/single parent, mother’s parity, child’s Aboriginality, whether child speaks English as a second language, highest level of maternal school education, highest level of occupation of either parent, area-level disadvantage, and geographical remoteness; in addition to the covariates included in Model 2, Model 3 adjusts for antenatal care visit before 20 weeks gestation, smoking during pregnancy, and preschool/day care attendance in the year before school. AEDC, Australian Early Development Census.

Fig 3. The absolute risk of developmental vulnerability on the language and cognitive skills and communication skills and general knowledge domains of the AEDC, and vulnerability on ≥1 AEDC domains, for every year of maternal age at childbirth between 15 and 45 years.

Model 1 includes adjustment for the child’s age at school entry, sex, and AEDC year; in addition to the covariates included in Model 1, Model 2 adjusts for private health insurance/patient status, mother born in Australia/overseas, mother partnered/single parent, mother’s parity, child’s Aboriginality, whether child speaks English as a second language, highest level of maternal school education, highest level of occupation of either parent, area-level disadvantage, and geographical remoteness; in addition to the covariates included in Model 2, Model 3 adjusts for antenatal care visit before 20 weeks gestation, smoking during pregnancy, and preschool/day care attendance in the year before school. AEDC, Australian Early Development Census.