Geographic variations in probability of pregnancy in four cities of France.

Background: Several studies have described geographic variations in human fecundability, but this phenomenon has almost exclusively been studied at an international level rather than within a given country. Our aim was to describe geographic variations in fecundability, the monthly probability of pregnancy, between four cities of France.

Methods: We conducted a cross-sectional study in four French maternity units from Toulouse, Rennes, Lyons and Paris, among partners of pregnant women.

Selection bias in semen studies due to self-selection of volunteers.

Background: Reports of a secular decrease in semen quality remain controversial, particularly due to the possibility of selection bias. We aimed to describe the potential bias due to self-selection of volunteers in semen studies involving fecund men.

Methods: Using data from the French multicentre study REPRHOM, we compared the characteristics of the partners of pregnant women for three levels of participation: completion of a refusal questionnaire (n = 698), agreement to complete the study questionnaires only (n = 676) and agreement to complete the study questionnaires and give a semen sample (n = 331, 13% of the subjects approached).