Menstrual cycle pattern and fertility: a prospective follow-up study of pregnancy and early embryonal loss in 295 couples who were planning their first pregnancy

Objective: To characterize how the menstrual cycle pattern relates to ferti lity regardless of potential biases caused by inappropriate coital timing d uring the menstrual cycle or early embryonal loss. Design: Prospective follow-up study. Setting: Healthy couples recruited throughout Denmark. Patient(s): Two hundred ninety-live couples who were planning their first p regnancy were followed up from the discontinuation of birth central until a pregnancy was recognized within six menstrual cycles. Early embryonal loss es were detected by changes in urinary hCG levels. Intervention(s): None. Main Outcome Measure(s): The probability of pregnancy occurring within one menstrual cycle (fecundity). Result(s): In women who had a cycle length that differed by >10 clays from the usual cycle length, fecundity was approximately 25% that of women who h ad no variation (odds ratio 0.25, 95% confidence interval 0.09-0.68). When the combined effect of cycle variation and cycle length was assessed, cycle variation was a persistent strong predictor of fecundity. Conclusion(s): The mechanisms of the present findings probably are female f unctional disturbances in ovulation, conception, implantation, or sustained pregnancy, linked with variable menstrual cycle length. Thus. identificati on of medical and environmental causes of abnormal menstrual cycle patterns may provide clues to the causes of infertility. Moreover, the menstrual cy cle pattern also should be taken into consideration in the clinical decisio n-making process. (Fertil Steril(R) 1999;71:490-6. (C)1999 by American Soci ety for Reproductive Medicine.).