Dunson, D. B., & Stanford, J. B. (2007). Effects of sexual intercourse patterns in time to pregnancy studies. American Journal of Epidemiology, 165(9), 1088-1095. https://doi.org/10.1093/aje/kwk111
Dunson DB, Stanford JB. Effects of sexual intercourse patterns in time to pregnancy studies. Am J Epidemiol. 2007;165(9):1088-1095. doi:10.1093/aje/kwk111
Dunson, D. B., and J. B. Stanford. "Effects of sexual intercourse patterns in time to pregnancy studies." American Journal of Epidemiology, vol. 165, no. 9, 2007, pp. 1088-1095.
National Institute of Environmental Health Sciences00j4k1h63
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RRM Academy Synopsis
Intercourse timing shifts time to pregnancy in simulated couples
A 2007 simulation of couples with equal intercourse frequency found that intercourse timing in the fertile window changes time to pregnancy in the model. For higher-fecundity couples having intercourse twice per week, mean time to pregnancy was 1.9 cycles when weighted toward the most fertile days. Even spacing took 3.0 cycles. Weighting toward the least fertile days took 4.9.
Key Findings
Higher-fecundity couples at a daily intercourse probability of 0.28 (twice per week) averaged 1.9, 3.0 and 4.9 cycles to pregnancy under patterns 1, 2 and 3.
Higher-fecundity couples: the fecundability ratio, pattern 1 to pattern 2, was 1.6 at a frequency of 0.28 and 2.0 at 0.1.
Lower-fecundity couples: the fecundability ratio, pattern 1 to pattern 2, was 1.4 at a frequency of 0.28 and 1.7 at 0.1.
With the ratio held at 1.7 for pattern 1 versus pattern 2, mean time to pregnancy differed by 2.3 months at cycle viability 0.3 and 6.8 months at 0.1.
Interpretation
This modeling study built equations from day-specific pregnancy probabilities recorded in a European diary study of 782 couples, then varied intercourse patterns across the fertile window. Pattern 1 weights intercourse toward the most fertile days. Pattern 2 spreads it evenly. Pattern 3 weights it toward the least fertile days. The authors note that real differences in intercourse patterns among groups are unknown, since studies seldom collect this data. The findings support further studies that measure actual intercourse timing alongside time to pregnancy.
RRM Context
Fertility awareness methods estimate ovulation timing from daily observations. The authors call daily urine collection the gold standard. They name three simpler ways: basal body temperature, home urine hormone monitors and mucus checks. Mucus checks are easy to learn, need no devices and have accuracy similar to temperature. Daily charting can supply the timing data these studies seldom collect.
Our editorial summary of this paper, not the article's abstract.
Abstract
Time to pregnancy, typically defined as the number of menstrual cycles required to achieve a clinical pregnancy, is widely used as a measure of couple fecundity in epidemiologic studies. Time to pregnancy studies seldom utilize detailed data on the timing and frequency of sexual intercourse and the timing of ovulation. However, the simulated models in this paper illustrate that intercourse behavior can have a large impact on time to pregnancy and, likewise, on fecundability ratios, especially under conditions of low intercourse frequency or low fecundity. Because intercourse patterns in the menstrual cycles may vary substantially among groups, it is important to consider the effects of sexual behavior. Where relevant and feasible, an assessment should be made of the timing and frequency of intercourse relative to ovulation. Day-specific probabilities of pregnancy can be used to account for the effects of intercourse patterns. Depending on the research hypothesis, intercourse patterns may be considered as a potential confounder, mediator, or outcome.
