title: Feasibility of the current-duration approach to studying human fecundity.
abstract: Approaches for monitoring time trends in couples' fecundity and for studying its sensitivity to environmental factors are needed. Two approaches rely on the inclusion of a cross-sectional sample of couples currently "at risk" of pregnancy either with follow up (prevalent cohort) or without follow up (current-duration design). To illustrate the feasibility of the current-duration design, we contacted a random sample of 1204 French women age 18 to 44 years in 2004 and recruited those who were currently having unprotected sexual intercourse. The current duration since the beginning of unprotected intercourse was defined for 69 women (5.7%). An additional 15 women (1.2%) were planning to start trying to become pregnant within the next 6 months. Parametric methods allowed, based on current duration of unprotected intercourse, estimation of fecundity as if the couples had been followed prospectively. The estimated proportion of couples not pregnant after 12 months of unprotected intercourse was 34% (95% confidence interval [CI] = 15-54%). The accelerated-failure time model allows study of the influence of environmental factors on fecundity. As an illustration, tobacco smoking by the woman was associated with a doubling in the median duration of unprotected intercourse before pregnancy (adjusted time ratio = 2.4; 95% CI = 1.1-5.2). We quantified the influence of time trends in the prevalence of smoking on this estimate. We suggest ways to quantify or avoid other potential bias. In conclusion, it is possible to recruit a sample of couples currently having unprotected intercourse. The current-duration design appears feasible with approximately 5 times as many women eligible for study as for an incident cohort design.
authors.affiliation: Inserm, National Institute of Health and Medical Research, U569, IFR 69, Le Kremlin-Bicêtre, France. slama@vjf.inserm.fr
authors.forename: Rémy
authors.initials: R
authors.lastname: Slama
authors.forename: Béatrice
authors.initials: B
authors.lastname: Ducot
authors.forename: Lisbeth
authors.initials: L
authors.lastname: Carstensen
authors.forename: Christine
authors.initials: C
authors.lastname: Lorente
authors.forename: Elise
authors.initials: E
authors.lastname: de La Rochebrochard
authors.forename: Henri
authors.initials: H
authors.lastname: Leridon
authors.forename: Niels
authors.initials: N
authors.lastname: Keiding
authors.forename: Jean
authors.initials: J
authors.lastname: Bouyer
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D015982:Bias; D015331:Cohort Studies; D003075:Coitus; D003430:Cross-Sectional Studies; D005193:Family Planning Services / Q000379:methods; D005260:Female; D005298:Fertility; D006801:Humans; D008297:Male; D018579:Patient Selection; D011247:Pregnancy; D011336:Probability; D012907:Smoking / Q000009:adverse effects; D011795:Surveys and Questionnaires