Maternal age at delivery and fertility of the next generation.

BACKGROUND: While most known causes of infertility relate to the health of the woman and/or her partner, questions have been raised regarding the possible contributions of transgenerational or epigenetic factors. OBJECTIVE: The goal of this hypothesis-generating work was to examine whether Generation 1's (G1's) age at the delivery of G2 (Generation 2) was associated with G2's fertility in later life. METHODS: We conducted a retrospective cohort study of women (G2s) recruited online in 2016. A questionnaire queried G2s regarding demographics and fertility. The primary exposure was G1's age at G2's birth. Outcome measures included the following: 12-month infertility, time to pregnancy, and childlessness. The adjusted relative risk (RR) of G2 infertility and childlessness by G1 age at G2's birth was estimated through a modified Poisson regression approach. The fecundity odds ratio (FOR) for the association between G1's age at G2 birth and time to pregnancy for G2 was estimated by discrete-time survival models, with complementary log-log link. RESULTS: A total of 2,854 women enrolled. We found no association between G1 age at G2's birth and G2 infertility. Being born to a G1 aged 15-19 years was associated with a longer time to pregnancy for G2 (FOR 0.84, 95% confidence interval 0.72, 0.99), relative to being born to a G1 aged 20-24 years. We observed the suggestion of a possible increased risk of childlessness among G2s born to older G1s, but the estimate was imprecise. CONCLUSIONS: While being born to a G1 who was 15-19 years old was associated with an increase in G2 time to pregnancy, we found no association between G1 age at G2's birth and infertility and only the suggestion of a modest association with childlessness. These data suggest a possible subtle effect of G1 age at G2's birth on G2 fertility, which warrants further study.