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A luteal phase is a period of approximately 12 to 16 days between ovulation and the start of a woman’s next menstrual cycle. It is also often called days past ovulation or DPO. The primary connection between the luteal phase and pregnancy is that its length can help to determine fertility or whether implantation has occurred. During this time, body temperature rises slightly, thus creating a more hospitable climate for the fertilization of an egg. If a woman’s luteal phase is too short, the lining of the uterus will be expelled before the egg can be fertilized, resulting in an early miscarriage.
It can be beneficial to understand the connection between the luteal phase and pregnancy while attempting to conceive or to identify fertility problems. Women with a consistently short luteal phase — usually ten days or less — will have more difficulty conceiving than women who have a cycle that is around the average of 14 days. A luteal phase that is too short is called a luteal phase defect.
There are several possible reasons for an abnormally short luteal phase and pregnancy attempts that fail as a result of an inhospitable environment in the uterus. Overall, a short luteal phase is usually the result of insufficient progesterone in the system. This could be the result of inadequate development of follicles, which start the chain reaction that creates progesterone. The luteal phase could also be shorter because the corpus luteum, which is the blood that comes from the follicle that produces progesterone, fails to work properly. In other cases, the uterine lining may not respond to stimulation from the follicles and corpus luteum and thus fail to create the progesterone necessary to keep the fertilized egg in the uterine lining.
By charting her luteal phase, a woman can help to determine whether a luteal phase defect is the reason for her inability to conceive. Understanding her personal connection between the luteal phase and attempts to conceive, and then either ruling out or detecting a luteal phase defect, will arm a woman with the information necessary to determine the cause of fertility problems.
Unlike the first part of the menstrual cycle in which a woman ovulates, the luteal phase usually lasts the same number of days each cycle. Ovulation can be delayed by outside elements such as intense physical activity, stress, prescription drugs, and illness. The luteal phase may start late in a certain cycle, but it will still end after the typical number of days. For this reason, if a woman’s luteal phase appears to be running longer than usual, it is likely that the next menstrual cycle is not starting because she is pregnant.