Age effect: results from a detailed prospective study on daily fecundability

Abstract

Demographers, epidemiologists and clinicians have long been interested in the estimation of age-specific fecundability. With the progressive postponement of age at family formation in Western countries, this topic has recently become the focus of renewed attention. In order to correctly estimate the effect of biological ageing on fecundability it is crucial to collect detailed information through a rigorous study design and to apply suitable models for analysing time to pregnancy data. In this article we discuss some methodological problems concerning the study of fecundability and its dependence on biological ageing. We also present the Multinational Study in Daily Fecundability which has produced a very rich database with detailed behavioural and physiological information prospectively collected on every cycle. Finally, we review some results on age effects obtained from these data. Our findings show that the decline in fecundability from age 28 to age 33 is not statistically significant and very modest. The results presented here do not appear to be particularly alarming with regard to the postponement of conception of the first child from age 28 to 33. This postponement could however lead to attempts to conceive a second child after age 35, when fecundability starts to decrease rapidly and when the risk of genetic disorders increases.