Age and fecundability in a North American preconception cohort study

Abstract

Background There is a well-documented decline in fertility treatment success with increasing female age; however, there are few preconception cohort studies examining female age and natural fertility. In addition, data on male age and fertility is inconsistent. Given the increasing number of couples attempting conception at older ages, a more detailed characterization of age-related fecundability in the general population is of great clinical utility. Objective To examine the association between female and male age with fecundability. Study Design We conducted a web-based preconception cohort study of pregnancy planners from the United States and Canada. Participants enrolled between June 2013 and July 2017. Eligible participants were aged 21–45 years (females) or ≥21 years (males), and not using fertility treatments. Couples were followed until pregnancy or for up to 12 menstrual cycles. We analyzed data from 2,962 couples who had been trying to conceive for ≤3 cycles at study entry and reported no history of infertility. We used life-table methods to estimate the unadjusted cumulative pregnancy proportion at 6 and 12 cycles by female and male age. We used proportional probabilities regression models to estimate fecundability ratios, the per-cycle probability of conception for each age category relative to the referent (21–24 years), and 95% confidence intervals. Results Among females, the unadjusted cumulative pregnancy proportion at 6 cycles of attempt time ranged from 62.0% (age 28–30 years) to 27.6% (age 40–45 years); the cumulative pregnancy proportion at 12 cycles of attempt time ranged from 79.3% (age 25–27 years) to 55.5% (age 40–45 years). Similar patterns were observed among males, although differences between age groups were smaller. After adjusting for potential confounders, we observed a nearly monotonic decline in fecundability with increasing female age, with the exception of 28–33 years, where fecundability was relatively stable. Fecundability ratios were 0.91 (95% confidence interval: 0.74–1.11) for ages 25–27, 0.88 (95% confidence interval: 0.72–1.08) for ages 28–30, 0.87 (95% confidence interval: 0.70–1.08) for ages 31–33, 0.82 (95% confidence interval: 0.64–1.05) for ages 34–36, 0.60 (95% confidence interval: 0.44–0.81) for ages 37–39, and 0.40 (95% confidence interval: 0.22–0.73) for ages 40–45, compared with the reference group (ages 21–24 years). The association was stronger among nulligravid women. Male age was not appreciably associated with fecundability after adjustment for female age, although the number of men over age 45 years was small (n=37). Conclusion In this preconception cohort study of North American pregnancy planners, increasing female age was associated with an approximately linear decline in fecundability. While we found little association between male age and fecundability, the small number of men in our study over age 45 years limited our ability to draw conclusions on fecundability in older men.

Good practices for the design, analysis, and interpretation of observational studies on birth spacing and perinatal health outcomes

“…Public health recommendations on birth spacing reflect a balancing of risks associated with both short and long interpregnancy intervals. However, studies of interpregnancy interval and adverse outcomes, conducted among women with two or more births, miss an important consequence of delaying a subsequent pregnancy: that the rise in age‐related infertility may prevent the occurrence of a second birth . Thus, researchers should be cautious about making statements about optimal intervals based solely on their findings in a study associating interpregnancy interval with adverse outcomes among women who had two or more births.…”

Perceived Subfecundity and Contraceptive Use Among Young Adult U.S. Women

“…First, while women were not explicitly asked about their “fecundity,” the vignette incorporates the definition of fecundity (i.e., the biological ability to have a child). Second, prospective cohort studies indicate that the objective probability of pregnancy after a year of unprotected intercourse ranges from 75% to 85%; thus, most women in the NLSY sample had a high biological likelihood of having a child within the two‐year time frame specified in the vignette. Lastly, by asking women to imagine that they wanted a child, the measure attempted to lessen the influence of women's underlying fertility preferences or desires at the time of the survey.…”

Menstrual bleeding, cycle length, and follicular and luteal phase lengths in women without known subfertility: A pooled analysis of three cohorts

“…Age and parity are two factors known to influence menstrual cycle characteristics. 5,6 There are few recent studies using complete detailed daily diary data of sufficient duration to assess normal within-woman variability of menstrual characteristics, using appropriate statistical methods to account for different numbers of cycles per woman. [7][8][9] The objective of this study was to describe total cycle length; anovulatory cycles; follicular and luteal phase lengths; and days and intensity of menstrual and non-menstrual bleeding, while assessing variability between-women and within-woman variability, in relation to age and parity.…”