Right-sided ovulation favours pregnancy more than left-sided ovulation.

The aim of this study was to evaluate whether frequency of ovulation and fertility potential of oocytes from the two ovaries differed in regularly menstruating women (1057 cycles of 856 fertile women and 1033 cycles of 258 infertile women). For both fertile and infertile women ovulation from the right ovary occurred more often than from the left ovary (55 versus 45%; P: < 0.005). In infertile women follicular phase length was similar for right- and left-sided ovulation. However, infertile women treated with intrauterine insemination (IUI) or in-vitro fertilization (IVF) showed a pregnancy rate in connection with right-sided ovulation (13%) which was higher than that of left-sided (9%). The ratio of pregnancies deriving from the right ovary per total number of pregnancies was similar in infertile and fertile women (64.6%, 73/113 and 63.4%, 361/569 respectively). The ratio of pregnancies from right-sided ovulation (approximately 64%) per total number of pregnancies was higher than that of right-sided ovulation (approximately 55%) during non-pregnant cycles (P: < 0.0001). The implantation rate in right-sided ovulation seemed to be higher than in left-sided one, since IVF data showed a lower frequency (P: = 0.03) of pre-embryo formation from right-sided ovulation than left-sided. Mid-luteal serum oestradiol and testosterone were higher (P: < 0.05) in right-sided ovulation than left-sided. Taken together, in both fertile and infertile women the fertility potential of oocytes from the right ovary surpasses that of the left ovary.