The Role of Progesterone in Fertility

Welcome back to Fertile Fridays!! Since I have no interesting news yet in either direction after our IUI last week (other than a case of butterflies!), I thought today I’d give a little summary of the role of progesterone in fertility.

Progesterone is one of our key reproductive hormones. Both men and women produce progesterone, but women in higher quantities. Typically, during a 28-day cycle, progesterone stays quite low in the first half of the cycle. Estrogen is the hormone that builds in the first half of the cycle (called the follicular phase), and in tandem with a surge of luteinizing hormone (LH), triggers ovulation. During the second half of the cycle, known as the luteal phase, progesterone increases, and theoretically stays high for those couple of weeks. If conception does not occur, progesterone levels will fall quite suddenly and menses will start.

Progesterone is necessary for the development of the uterine lining, enabling implantation of a fertilized egg. That is why it is produced in higher amounts in the second half of the menstrual cycle where fertilization theoretically could have occurred. So in conception, having the sperm find the egg is one thing, having it fertilize the egg is another, and have the egg/ sperm combo (now officially an embryo) find its way to a cushy comfortable home where it can settle in and grow in a healthy environment, that’s another thing again. In fact, many conceptions occur but do not become ongoing pregnancies because the embryo cannot or does not implant and take root.

So, for ovulation to occur, healthy estrogen levels, along with FSH and LH, are key. For the uterine lining to build to be able to host an embryo, progesterone is key. Once baby is growing, progesterone is also produced by the placenta to maintain the pregnancy in a healthy way.

Here’s the problem. Increasingly, women experience suboptimal progesterone levels. Ovulation might be occurring, but if progesterone is not high enough in that luteal phase, the proverbial room is not furnished for implantation. This may be quite difficult to think about, but it is possible that many pregnancies occur but “miscarry” in the early days or weeks because of this shortage of progesterone.

Progesterone levels tend to start falling in the mid-30’s/ early 40’s, so with many women having children later, this might be more of a problem now than in past generations where women were having kids in their 20’s and early 30’s. Adrenal stress can also play a role, as the adrenals produce 25% of all estrogen and progesterone in pre-menopausal women (increasing to around 33% in post-menopausal women).

Testing for progesterone levels should be done between days 17 and 20 of the menstrual cycle. If levels appear low, the best herbal option is Vitex (also known as Chaste tree). However, women who are trying to conceive and have low or low-normal progesterone levels might want to supplement with progesterone itself. This can be done either through a liquid progesterone – I like this one which is best taken under the tongue, or a cream rubbed on the skin. For really low levels, it might be warranted to have a higher potency, bio-identical one that would be prescribed through a doctor.

Often women who have had previous miscarriages are given progesterone, as it can help maintain pregnancy. Vaginal suppositories are the most common form given once pregnancy is confirmed, given for the first trimester.

Progesterone is a key hormone for pregnancy, and a deficiency, even a level at the lower end of “normal” range on a lab test, might be a reason for infertility. Since most of the time we wouldn’t know if we weren’t conceiving at all, versus conceiving but then not maintaining the pregnancy, looking at progesterone levels is an important step.