Contralateral ovulation shortens follicular phase length and favours pre-embryo development during ovarian stimulation with clomiphene citrate.

The present study was undertaken to evaluate whether the site of ovulation affects the following follicular phase length and pre-embryo development during infertility treatment with ovarian stimulation using clomiphene citrate. A total of 363 cycles in 97 patients undergoing infertility treatment (182 intrauterine insemination (IUI) cycles in 60 patients and 181 in-vitro fertilization (IVF) cycles in 52 patients) were studied. The cycles were divided into two main groups: preceding unilateral ovulation (PUO) and preceding bilateral ovulation (PBO). In the PUO group, the cycles were subdivided into contralateral ovulation, bilateral ovulation and ipsilateral ovulation. In IVF cycles alone, bilateral ovulations were further divided into bilateral ovulation-contralateral side and bilateral ovulation, ipsilateral side. Contralateral ovulations were seen in 134 of 240 cycles (56%), excluding bilateral ovulation and PBO. The follicular phase length in contralateral ovulation (16.2 +/- 2.6 days, mean +/- SD) was significantly (P < 0.05) shorter than that of ipsilateral ovulation (16.9 +/- 2.8). There were no significant differences of follicular phase length among contralateral ovulation, bilateral ovulation and PBO. Of IVF cycles including contralateral ovulation-ipsilateral ovulation and bilateral ovulation a total of 107 preovulatory follicles was assessed in the contralateral side (contralateral ovulation + bilateral ovulation-contralateral side) and 97 in the ipsilateral side (ipsilateral ovulation + bilateral ovulation, ipsilateral side). The oocyte retrieval rate (88%), fertilization rate (84%), cleavage rate (95%), embryo transfer rate (70%) of contralateral follicles were higher than those of ipsilateral follicles (71, 62, 86, 38% respectively) and those of PBO (76, 62, 87, 41% respectively). The total pregnancy rate of both IUI and IVF did not differ among contralateral ovulation (15%), ipsilateral ovulation (8%), bilateral ovulation (11%) and PBO (10%). The results confirm and extend our previous findings in natural cycles, suggesting that local ovarian factors, e.g. from corpus luteum, affect the health of preovulatory follicle and the enclosed oocyte in the same ovary (ipsilateral) negatively. Contralateral selection of preovulatory follicles in the succeeding cycle shortens the follicular phase length and favours pre-embryo development. The chance of conceiving during ovarian stimulation with clomiphene citrate may thus be affected by the site of ovulation in the previous cycle.