Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation.
Level 3 - non-randomized controlled study
Secondary statistical modeling and re-analysis of observational cohort data
PubMed 10402400 · doi:10.1093/humrep/14.7.1835
What was done
Researchers applied a statistical model to correct for measurement error in identifying the day of ovulation and re-estimate day-specific fecundability and the duration of the fertile window. The model was applied to two historical datasets: a study of Catholic couples using natural family planning in London (1950s–1960s) who tracked ovulation via basal body temperature shifts, and a study of couples attempting pregnancy in North Carolina (early 1980s) who monitored ovulation via urinary hormone assays.
What was found
The abstract reports no exact numerical probabilities. After controlling for measurement error, both datasets demonstrated an identical 6-day fertile interval. In both cohorts, the estimated probability of clinical pregnancy peaked on the day immediately prior to ovulation and dropped to near zero following ovulation.
Why it matters
Shows that differing estimates of the fertile window across historical studies were likely artifacts of measurement error, confirming that human conception is primarily restricted to the six days leading up to and including ovulation.
Limits
The abstract provides no sample sizes, numerical fecundability estimates, or confidence intervals. The analysis relies on statistical assumptions to correct for measurement error rather than direct biological verification of follicular rupture, and it evaluates historical cohorts with disparate populations and study goals (pregnancy avoidance vs. pregnancy seeking).
Cited by
- supports Intercourse during the two days before and the day of ovulation carries a 20% to 30% probability of conception, whereas intercourse the day after ovulation has a 0% probability.