Progesterone is essential for establishing and maintaining a healthy pregnancy. Levels of progesterone increase rapidly with ovulation and if fertilisation occurs they continue to rise during the first and second trimesters, before plateauing in the third. Initially progesterone is secreted by the corpus luteum, before the placenta takes over at approximately ten weeks of pregnancy. The corpus luteum is a temporary, endocrine-secreting structure located on the wall of the ovary. It is what remains of the ovarian follicle after the ovum has been released. If fertilisation does not occur, the corpus luteum will disintegrate and a new one will form with the next menstrual cycle. If the ovum is fertilised, it will release a hormone called human chorionic gonadotropin, which signals to the corpus luteum to continue secreting progesterone. Progesterone prepares the uterus for implantation; it does this by maintaining a thick lining, with a good blood supply, providing optimal conditions for foetal development.
One of the main symptoms of PCOS is anovulation and this causes a deficiency in progesterone. Many women with PCOS struggle to conceive. In fact, the condition accounts for approximately 80% of anovulatory infertility cases. With dietary and lifestyle changes there is a good chance that PCOS symptoms can be reversed, however, it is still essential to maintain high progesterone levels during pregnancy. Low progesterone increases the risk of miscarriage in all women, but women with PCOS are particularly vulnerable.
If lifestyle changes do not work, many women consider using medication to help them conceive. One widely used example is clomiphene citrate. This anti-oestrogen drug has a high success rate at inducing ovulation (approximately 80%); although subsequent pregnancy rates are significantly lower (35-40%). It has been suggested that one way of boosting pregnancy rates could be via progesterone supplementation. The hormone is already used frequently as an adjunct in assisted-conception treatment.
Despite its key role in pregnancy, progesterone supplementation does not appear to improve the rates of live births in women experiencing recurrent miscarriage. Perhaps because to date the supplements have only been given once the pregnancy is established. These results are disappointing, but should not detract from the importance of maintaining high levels of endogenous progesterone during pregnancy.
- Balen, A H, et al. “The Management of Anovulatory Infertility in Women with Polycystic Ovary Syndrome: an Analysis of the Evidence to Support the Development of Global WHO Guidance.” Human Reproduction Update, vol. 22, no. 6, Nov. 2016, pp. 687–708., doi:10.1093/humupd/dmw025.
- Coomarasamy, A, et al. “A Randomized Trial of Progesterone in Women with Recurrent Miscarriages.” New England Journal of Medicine, vol. 373, no. 22, 26 Nov. 2015, pp. 2141–2148., doi:10.1056/NEJMoa1504927.
- Gotter, A. “Low Progesterone: Complications, Causes, and More.” Healthline, www.healthline.com/health/womens-health/low-progesterone. Medically reviewed by Holly Ernst, PA-C on August 25, 2016.