Luteal Phase Defect occurs when the time between ovulation and a women’s cycle starts is less than 10-12 days in length. Usually women will have shorter cycles but this is not always the case. The concern is that a fertilized egg will not have enough time to fully implant into the uterine wall before it begins to shed at the next cycle. The biggest cause of luteal phase defect is low progesterone levels and it is important to have your progesterone levels checked between days 19 and 21 of your cycle. Progesterone is produced by the ovary after ovulation has occurred to help maintain uterine lining so the fertilized egg can implant and start to develop; an important first step to maintaining pregnancy.