Factors affecting time to pregnancy.

BACKGROUND: Both lifestyle factors and occupational and environmental factors have been suggested to affect the female reproductive system. In the present study, the separate and joint effects of several such factors are investigated.
METHODS: Information on time to pregnancy (TTP) was available for 1578 women randomly selected from the general Swedish population. The information was collected retrospectively by using self-administered questionnaires. By means of logistic regression of survival data, fecundability odds ratios were determined for many factors. Multivariate models were used to determine which factors had the most impact on TTP.
RESULTS: Several lifestyle factors were found to associate with TTP. However, only use of oral contraceptives prior to attempting to conceive, menstrual cycle length, age at conception and parity remained in the multivariate models. Together, these factors explained 14% of the variance in TTP. Excluding first and second month conceptions, only age at conception and menstrual cycle length remained in the multivariate models, together explaining only 8% of the variance in TTP.
CONCLUSIONS: Although information on several factors was available, the multivariate model explained only a small fraction of the variation in the observed time to pregnancies. Furthermore, female biological factors seemed more important predictors of TTP than lifestyle factors.