Ovulation occurs about 14 days before the next menstrual period. After ovulation, the estrogen in the follicular fluid is released into the abdominal cavity, causing a brief drop in circulating estrogen, i.e. a transient drop in estrogen levels, causing the endometrium to flake off in small amounts, resulting in brownish leucorrhoea, but the amount is usually small and will return to normal after 3-5 days.