IS THERE SEASONALITY IN HUMAN OVULATION

To study seasonality in human ovulation in a direct way, we measured t he occurrence of ovulation in infertile patients with spontaneous mens trual cycles (<6 weeks) who visited the fertility clinic at the Univer sity Hospital Nijmegen in the Netherlands for the first time in 1991 o r 1992 (n = 407). Ovulation was detected using serial transvaginal ult rasound and midluteal progesterone measurement and was performed durin g one screening cycle. The frequency of ovulatory cycles per month var ied from 73 % to 93 % (not statistically significant). No seasonal pat tern in ovulation was found in subfecund Dutch women with spontaneous menstrual cycles. This finding was not confounded by the effects of ag e of the women, body mass index, or disorders that could influence ovu lation.