If no conception occurs in the 24 hours following ovulation, the unfertilized egg will still continue its journey through the fallopian tube and into the uterus, but it will not implant into the uterine wall. Levels of estrogen and progesterone begin to fall about 10 days after ovulation and if there is not a signal from a fertilized egg to keep them high, levels of these two hormones continue to drop until they are low enough to signal the initiation of menstruation and the thickened lining of the uterus begins to shed. This usually occurs about 14 days after the egg was initially ovulated. The first day of menstruation is also day one of a new cycle and estrogen levels will begin to rise again, starting the process anew.