SEASONAL-VARIATION IN THE TIME TO PREGNANCY - A SECONDARY ANALYSIS OF3 DANISH DATABASES

Three Danish databases were reanalysed to investigate seasonal variati on in the time to pregnancy. Information was available on cohorts of w omen selected on the basis of union membership or residence in a given area: textile workers in Denmark (with 1,053 first and 1,771 second p regnancies), pharmacy assistants in Denmark (with 734 first and 725 se cond pregnancies) and pregnant-women in the 36th week of pregnancy in two Danish cities (with 3,657 first and 3,526 second pregnancies). The influence of the season was of primary interest, because it is presum ed to cause impaired ovarian function and hence a prolonged time to pr egnancy. Furthermore, we studied whether the waiting time was prolonge d in other situations with possibility of decreased ovarian function: in young and older women. In general, seasonality in the time to pregn ancy based on the time of conception was found with a higher chance of a prolonged waiting time before conceiving in February-April and a lo wer chance of a prolonged waiting time before conceiving in August-Oct ober. This association was not distorted by the age of the women or di abetes mellitus. A prolonged time to pregnancy was found in women of 3 0 years or older. Women of 20 years or younger did not have a prolonge d waiting time, but most of them were well beyond the age of menarche and thus beyond the period of impaired ovarian function. On a populati on level, there was evidence for seasonality in the time to pregnancy, which is compatible with seasonal variation in pregnancy planning as well as with biological influences.