Since the 1980s, there has been a significant increase in the average age at which women in industrialized nations have their first child. Advanced maternal age, medically defined as ages 35 and up, has in a number of studies shown negative association with infant health, and potentially, development in later life. However, data from three separate birth cohorts in the United Kingdom (1958, 1970, and 2001) indicated a marked increase in the cognitive ability of first-born children over time. At face value, this appears to be a disconnect: Shouldn’t the trend towards later child-bearing correlate to lower cognitive abilities among first-borns? A trio of researchers explored what was behind the unexpected results and recently published their results in the International Journal of Epidemiology.
The three birth cohorts were studied separately for different longitudinal research projects and each included more than 16,000 randomly sampled children born in specific windows of time. Cognitive ability of the children was assessed at the ages of 10 or 11 using different tests of verbal cognition depending on the cohort. The researchers in the present study combined the data and standardized the three different test results to ensure the best comparability between the diverse data sources. The most common age range in which women were giving birth in both 1958 and 2001 was 25-29, so that range was chosen as the comparison for the advanced age cohort. The researchers zeroed-in on first-borns in both age ranges. The study included adjustments for socio-demographic characteristics (married or single, income, education at time of birth, etc.) and health behaviors before and after pregnancy.
The results: First children born to younger mothers performed higher than peers born to older mothers in both the 1958 and 1970 cohorts, followed by a complete reversal of that performance outcome for the 2001 cohort.
How can it be that advanced maternal age went from being a negative influence on kids’ cognitive ability to a positive influence in less than 30 years? Although not addressed directly in the study, one part of the answer is likely to be the benefits of living in the 21st century—better medicine, hygiene, and reproductive science included. But the researchers posit that since first-born children typically have access to more maternal resources—both material support and things like attention—the trend toward older first births puts that positive variable ahead of the adverse variable of “advanced maternal age” and leads to the reversal. Additionally, older mothers are more likely to be established in their own education, career, and life, whatever level they have achieved. In short, later first births generally mean smaller ultimate family size, resulting in more resources for children and less competition for those resources down the line. These additional resources are enough to overcome the remaining potential negatives of advanced maternal age.
The researchers caution that their study looked at only a few cohorts in one nation and that more study is needed to better understand the link between timing of child bearing and its impact on later development. If the results are replicated with additional research, however, these findings could help bolster policymakers’ efforts to push adult stability as a key to child academic ability. Perhaps a push like the one proposed in the success sequence could nudge this phenomenon even further.
SOURCE: Alice Goisis, Daniel C. Schneider, Mikko Myrskalä, “The reversing association between advanced maternal age and child cognitive ability: evidence from three UK birth cohorts,” International Journal of Epidemiology (February, 2017).
