High ovarian response in Yoruba African women during ovulation induction for assisted conception

Fertile Yoruba women from western Nigeria have a much higher incidence of naturally conceived multizygotic twin and triplet pregnancies than Caucasians. The objective of the present study was to determine whether there are differences between infertile Yoruba and Caucasian women in terms of ovarian response in stimulate cycles for assisted conception. A total of 11 Yoruba women were scheduled for 14 in-vitro fertilization (IVF) and one gamete intra-Fallopian transfer (GIFT) cycles from 1990 to 1992. The Caucasian group consisted of 209 women scheduled for 213 IVF and 22 GIFT cycles during the same period. Buserelin, 500 micrograms subcutaneously daily, was started in the mid-luteal phase to achieve pituitary desensitization. Ovarian stimulation was with variable amounts of menopausal gonadotrophins. Human chorionic gonadotrophin (HCG) was given to trigger the ovulatory process. The Yoruba and Caucasian groups were similar in age and body weight, but significantly more Yorubas (45 versus 11%; P < 0.005) had ultrasound features of polycystic ovary syndrome (PCOS). The serum oestradiol concentration (3024 versus 2058 pg/ml; P < 0.05) and number of follicles > 14 mm in diameter (15.5 versus 9.5; P < 0.05) on the day of HCG were higher in the Yoruba group. The ovarian hyperstimulation syndrome (OHSS) was also more prevalent in the Yoruba group (20 versus 5%; P < 0.05). No difference was found in clinical pregnancy or embryo implantation rates. These results show a higher tendency toward exaggerated ovarian response in infertile Yoruba than Caucasian women, associated with a higher prevalence of PCOS. The risk of developing symptomatic OHSS is higher in Yoruba women.