Ovulation pattern in successive cycles in the baboon

The purpose of this study was to determine if the selection of the side on which ovulation occurs in successive cycles is a random event. Forty-seven baboons were observed for four consecutive cycles and 37 for two to three consecutive cycles. Side of ovulation was determined by laparoscopic examination. Of the 286 cycles studied, 146 cycles (51 %) showed ovulations on the left side and 140 cycles (49 %) on the right. Analysis of the data using two consecutive ovulations in 286 cycles revealed that the selection of the side of ovulation is a random event. However, when four consecutive ovulations observed in 47 baboons were analyzed, it was found that the observed pattern of ovulation was different from that expected from random chance (p>0.05). There are 16 possible combinations in a sequence of four ovulations. Eight of 47 baboons (17 %) ovulated on the same side for four consecutive cycles, 15 baboons (32 %) ovulated three times on the same side for four ovulations, and 24 baboons (51 %) showed two ovulations on each side. Alternation of ovulation in a sequence of four consecutive ovulations was observed 48 times (25.5 %) and alternation of ovulation in two consecutive cycles was observed 106 times (51 %).