Age and fecundability in a North American preconception cohort study.
Level 3 - non-randomized controlled study
Prospective observational cohort study
PubMed 28917614 · doi:10.1016/j.ajog.2017.09.002
What was done
A web-based prospective preconception cohort study enrolled pregnancy planners from the United States and Canada between June 2013 and July 2017. Participants were 21-45 years old (female) or 21 years and older (male), had not used fertility treatments, and reported no history of infertility. The analysis included 2,962 couples who had been trying to conceive for 3 or fewer cycles at study entry, followed until pregnancy or up to 12 menstrual cycles. Life-table methods estimated unadjusted cumulative pregnancy proportions at 6 and 12 cycles, and proportional probabilities regression models estimated fecundability ratios adjusted for confounders relative to female age 21-24 years.
What was found
Unadjusted cumulative pregnancy proportions among women at 6 cycles ranged from 62.0% (age 28-30) to 27.6% (age 40-45), and at 12 cycles ranged from 79.3% (age 25-27) to 55.5% (age 40-45). Adjusted fecundability ratios relative to women aged 21-24 years were 0.91 (95% CI, 0.74-1.11) for ages 25-27; 0.88 (95% CI, 0.72-1.08) for ages 28-30; 0.87 (95% CI, 0.70-1.08) for ages 31-33; 0.82 (95% CI, 0.64-1.05) for ages 34-36; 0.60 (95% CI, 0.44-0.81) for ages 37-39; and 0.40 (95% CI, 0.22-0.73) for ages 40-45. The association was stronger in nulligravid women. Male age was not appreciably associated with fecundability after adjusting for female age.
Why it matters
This study provides prospective estimates of natural conception rates by age in the general population outside fertility clinic settings. It quantifies the timing and magnitude of natural fertility decline, showing a marked drop after age 36 while 55.5% of women aged 40-45 still conceived within 12 cycles.
Limits
The web-based cohort design relied on self-reported data. The study had very few older men (only 37 men older than 45 years), limiting conclusions on male age effects. Restricting enrollment to couples who had been attempting conception for 3 or fewer cycles without a history of infertility may introduce selection bias toward relatively fecund older individuals.
Cited by
- contradicts If a woman does not have a child by age 30, her lifetime probability of ever having a child falls below 50% (or around 48%).
- context A woman's ability to conceive declines linearly starting from age 20.