CONTRALATERAL SELECTION OF DOMINANT FOLLICLE FAVORS PREEMBRYO DEVELOPMENT

Ovulation was studied using vaginosonography in a total of 410 natural cycles of 123 women undergoing infertility treatment [267 intrauterin e insemination (IUI) cycles of 103 women and 143 in-vitro fertilizatio n (IVF) cycles of 50 women], None of the women received ovarian stimul ation. Each follicle was measured daily from 14 mm in diameter until f ormation of corpus luteum or oocyte retrieval. Contralateral ovulation as compared with the preceding cycle occurred in 57% of the 410 cycle s, Contralateral ovulations occurred in 72% of cycles with a follicula r phase <13 days, In cycles with a follicular phase of >14 days, ovula tions occurred at random. The length of follicular phase in contralate ral ovulation cycles (15.2 +/- 3.2 days) was significantly (P < 0.05) shorter than that of ipsilateral ovulation cycles (15.8 +/- 2.8), Duri ng the 57% contralateral ovulations in 143 IVF cycles, the rates of oo cyte retrieval (89%), fertilization (69%), cleavage (90%) and embryo t ransfer (56%) were significantly higher than those of ipsilateral ovul ations (69, 51, 64 and 23% respectively). The pregnancy rate of contra lateral ovulations (9%) was also higher, though not significantly, tha n that of ipsilateral ovulations (3%), although the pregnancy rates pe r transfer were similar (16 and 14% respectively), The total pregnancy fate of both IUI and IVF was higher in contralateral than in ipsilate ral ovulation cycles (8.1 and 4.0% respectively), The dominant follicl es in contralateral ovulation cycles showed significantly higher oestr adiol/androstenedione ratio (P < 0.025) and oestradiol/testosterone androstenedione ratio (P < 0.025), and lower androstenedione (P < 0.05 ) than those of ipsilateral ovulation cycles, There was no significant difference in oestradiol, progesterone and testosterone, These result s indicate that the dominant follicles in contralateral ovulation cycl es are healthier than those of ipsilateral ones, Local intra-ovarian f actors, e.g. from the corpus luteum, may negatively affect the health of the dominant follicle and the enclosed oocyte, Therefore contralate ral selection of the dominant follicle in the succeeding cycle may fav our pre-embryo development, The chance of conceiving during a natural cycle may he affected by the site of ovulation in the preceding cycle.