Luteal phase is defined as a period between ovulation and the establishment of a pregnancy onset of menses after two weeks. The main hormone which works in neutral phase is progesterone. The goal of taking progesterone is to help get the uterine lining ready for implantation and hopefully for the embryo implantation. It also may help prevent pregnancy loss.
In IVF progesterone will be start after oocyte retrieval. This will continue till the positive test result achieve. If result positive then and it will continue till first trimester (10-12 Weeks). Taking progesterone after embryo transfer also decreases chances of miscarriage, because some of the women have lower progesterone level which can cause miscarriage. So that's why doctor prescribe progesterone after embryo transfer. Furthermore during the IVF cycle, the use of medication to prevent ovulation, as well as the oocyte retrieval procedure, can cause the production of progesterone as compared to natural conception. Progesterone prepares the lining of the uterus (endometrium) to allow a embryo to stick or implant. If a pregnancy does not take place, progesterone levels will fall and you will have your period.
Progesterone’s most important functions are its role in thickening the lining of the uterus each month. The enriched endometrial lining is prepared to receive and nourish a fertilized egg. If a pregnancy occurs, progesterone is produced in the placenta and levels remain elevated throughout the pregnancy.
Progesterone supplements after IVF can be given in any form like vaginal gel once or twice per day, vaginal tablets twice or thrice per day, progesterone in intramuscular injections form (100 MG) once a day. Vaginal progesterone supplementation has good effects on frozen-thawed embryo transfer and can significantly increase the rate if implantation, delivery and live birth.