Embryo implantation during menstruation in the absence of adequate estradiol and progesterone support, with subsequent normal response to ovulation induction and superfetation.

OBJECTIVE: To report an unusual case of embryo implantation and superfetation.
DESIGN: Retrospective case analysis.
SETTING: Oak Brook Fertility Center. PATIENT(S): A 41-year-old woman underwent two consecutive ovarian stimulation cycles interrupted by a normal menstrual period. Ovulation and implantation occurred during both cycles. The first embryo conceived developed normally until term; the second failed to develop. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Retrospective analysis of stored blood samples for serum E2, P, and beta-hCG levels. RESULT(S): Rising beta-hCG levels during menstruation indicated normal embryonic implantation in the absence of adequate E2 and P support. During subsequent ovarian stimulation, there was a normal follicular and E2 response and normal ovulation in spite of the ongoing pregnancy. The second embryo, conceived during the second cycle of stimulation, implanted but failed to develop. CONCLUSION(S): This unusual case indicates that E2, P, and endometrial thickness requirements for successful implantation may not always be as critical as postulated previously. The absence of a decidual response might have facilitated superfetation.