Influence of cycle variability and coital frequency on the risk of pregnancy

Contraception. 1999 Sep;60(3):137-43. doi: 10.1016/s0010-7824(99)00073-6.

Abstract

Researchers have cautioned against generalizing results from contraceptive trials because these studies rely on self-selected participants meeting strict selection criteria who may differ from typical users. Using information collected on daily diaries, we reanalyzed data from the recently completed Reality female condom clinical trial to evaluate factors that influence the probability of pregnancy. Noncompliant women, women with less variable menstrual cycles (17-43 days), and women engaging in intercourse frequently (> or = 11 acts per month) were more likely to conceive during this 6-month trial. The adjusted hazard ratios and 95% confidence intervals for these three covariates were 6.1 (2.0-18.7), 7.2 (1.0-54.3), and 2.0 (0.7-5.3), respectively. The strict selection criteria used in this study failed to recruit a homogeneous cohort with respect to factors that influence the risk of pregnancy. The overall pregnancy rate does not pertain to individual study participants, but rather represent average effects for a population with the particular mix of characteristics found in this study. In particular, we not only confirm the well known importance of compliance and the obvious role of frequency of intercourse, but also demonstrate that women with cycles outside the range of 17-43 days appear to be at a much lower risk of pregnancy.

PIP: This article highlights the influence of cycle variability and coital frequency on the risk of pregnancy using data from the completed female condom trial. Daily diaries of women, which include coital frequency and menstrual cycle, were reanalyzed to evaluate the factors that affect the probability of pregnancy. A higher probability of pregnancy was reported among noncompliant women, women with less variable menstrual cycles, and women engaging in frequent intercourse during a 6-month trial. The adjusted hazard ratios and 95% confidence intervals for these three covariates were 6.1 and 2.0-18.7 (noncompliant women), 7.2 and 1.0-54.3 (less variable menstrual cycles), and 2.0 and 0.7-5.3 (frequent intercourse), respectively. The overall pregnancy rate obtained in this study represent average effects for a population with the particular mix of characteristics. This study appears to demonstrate a much lower risk of pregnancy for women with menstrual cycles outside the range of 17-43 days.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Age Factors
  • Coitus*
  • Condoms, Female
  • Educational Status
  • Female
  • Humans
  • Menstrual Cycle*
  • Parity
  • Pregnancy
  • Probability
  • Sexual Behavior
  • Time Factors