Thursday, December 18, 2014
The Luteal Phase
The luteal phase is the portion of the cycle after ovulation.
During the follicular phase, before ovulation, several follicles containing eggs start developing. Generally, only one egg matures completely and is released during ovulation. The left-over follicle becomes the corpus luteum.
The corpus luteum produces progesterone, which thickens the uterus lining, and supports pregnancy. The corpus luteum normally lasts 10-16 days before withering.
During the 10-16 days that the corpus luteum is active, the egg is guided by the fallopian tube from the ovary to the uterus. In order for fertilization to occur, egg and sperm must meet within 24 hours of ovulation. If the egg is not fertilized, then, when the corpus luteum stops producing progesterone at day 10-16, the drop in progesterone levels cause the uterine lining and unfertilized egg to shed (ie. a period).
If pregnancy occurs, the fertilized egg implants in the uterine lining, usually sometime after day 10. The hormone HCG (the hormone pregnancy tests use to identify pregnancy) causes the corpus luteum to continue producing progesterone for about 10 weeks, at which point the placenta takes over progesterone production. This continues to support the uterine lining until the end of the pregnancy.
The luteal phase varies in length between women, but each woman's luteal phase tends to stay the same length. If a woman's luteal phase extends three days longer than her typical length, or over 18 days, there is a very good chance that pregnancy has occurred. Luteal phases that are less than 10 days may cause fertility problems. A fertilized egg often takes more than 10 days to implant in the uterine lining. If the uterine lining sheds before implantation can occur, the pregnancy will not continue.