Cumulative incidence of infertility in a New Zealand birth cohort to age 38 by sex and the relationship with family formation.

Objective: To estimate the cumulative incidence of infertility for men and women in a population-based sample.

Design: Longitudinal study of a birth cohort.

Setting: Research unit.

Patient(s): A population-based birth cohort of 1,037 men and women born in Dunedin, New Zealand, between 1972 and 1973.

Intervention(s): None.

Main Outcome Measure(s): Cumulative incidence of infertility by age 32 and 38, distribution of causes and service use for infertility, live birth subsequent to infertility, and live birth by age 38.

Result(s): The cumulative incidence of infertility by age 38 ranged from 14.4% to 21.8% for men and from 15.2% to 26.0% for women depending on the infertility definition and data used. Infertility, defined as having tried to conceive for 12 months or more or having sought medical help to conceive, was experienced by 21.8% (95% confidence interval [CI], 17.7-26.2) of men and 26.0% (95% CI, 21.8-30.6) of women by age 38. For those who experienced infertility, 59.8% (95% CI, 48.3-70.4) of men and 71.8% (95% CI, 62.1-80.3) of women eventually had a live birth. Successful resolution of infertility and entry into parenthood by age 38 were much lower for those who first experienced infertility in their mid to late thirties compared with at a younger age.

Conclusion(s): Comparison of reports from two assessments in this cohort study suggests infertility estimates from a single cross-sectional study may underestimate lifetime infertility. The lower rate of resolution and entry into parenthood for those first experiencing infertility in their mid to late thirties highlights the consequences of postponing parenthood and could result in involuntary childlessness and fewer children than desired.