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

In this birth cohort, 21.8% of men and 26.0% of women had ever tried to conceive for 12 months or more or sought medical help to conceive by age 38.

Thea van Roode, Ph.D., Nigel Patrick Dickson, M.D., Alida Antoinette Righarts, M.Sc., Wayne Richard Gillett, M.D.

Volume 103, Issue 4, Pages 1053-1058


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

Longitudinal study of a birth cohort.

Research unit.

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


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.

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.

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.

  • jimdupree4

    The authors should be applauded for completing this very important study and helping provide population-based rates of infertility and infertility treatments. This data has been lacking in the literature.

    I have two questions for the authors. First, how do the authors explain the discrepancy between males and female reporting different rates of infertility at the 32 and 38 year time points? Is mismatch between age of partners an explanation? Second, could the authors comment about the typical infertility referral patterns/treatment relationships in New Zealand? I found it encouraging that males and females reported similar rates of infertility testing and treatment, but who typically provides the testing and treatments in the authors’ healthcare system?

    • Thea Van Roode

      Thank you for your interest in our paper, and this complimentary feedback.

      Regarding the sex difference in infertility rates, we have speculated that this may be due to differences in age of partners for men and women, as the men in our sample were more likely than women to report that their current partners that were more than five years younger. While these are not necessarily the partnersthey experienced difficulties conceiving with, this would fit with this
      explanation. However, the fact that the sex difference reduced when those who sought help were included could also indicate that the length of time they may have experienced difficulty conceiving was a less salient event for men than for
      women, whereas seeking medical help for infertility was more easily
      remembered. This would suggest that the true sex difference may be less pronounced.

      Regarding the second question, early referral to secondary care is the normal practice and is managed by a NZ wide referral guideline that begins with 12 months of infertility (earlier for older women) and the completion of standard testing including semen analysis, health screening tests for the woman (e.g. Rubella immunity etc) and tests for ovulation. At the primary care level, there is also an expectation of initiating weight improvement programmes for high and low BMI (<18≥32). At the secondary care level, testing is completed including for any endocrinopathy and tubal factor if indicated (by HSG or laparoscopy).
      Assisted reproductive procedures are carried out by tertiary providers and publicly funded treatment is governed by access criteria. Access to publicly funded ART is not possible for women 40 and older. However, overall ART volumes in NZ are lower than many other Western countries (e.g only about 40% of that available in Australia), with publicly funded IVF limited to
      2 cycles.
      Hope this is helpful. On behalf of the authors,

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