If you’re new to fertility awareness methods (FAM), you may have heard the term “corpus luteum” tossed around in casual conversation, but have no idea what it means. If you’ve taken a high school biology class, you may know that the term means “yellow body” (“corpus” meaning body and “luteum” meaning yellow) in Latin. But unless you’ve received a particularly thorough education in a fertility awareness method (FAM), and even if you have charted your cycle for over ten years like I have, you may well still wonder what exactly a corpus luteum is, and what significance it has for your health and fertility.
In this FAM Basics article, we’re going to cover everything you need to know about the corpus luteum, including its significance in two particular FAM contexts: luteal phase defects, and pregnancy.
What is a corpus luteum? First, the “backstory”
The corpus luteum is actually a byproduct of your cycle’s main event, i.e., ovulation. You may recall that there are two distinct phases in every cycle (with ovulation occurring in between): the follicular phase and the luteal phase. The follicular phase comes first, and takes place in one of your ovaries. While a few immature eggs (also known as ova or oocytes) out of the thousands in your ovary start growing within follicles (sacs) each cycle, they can’t all be ‘top dog’ and be released at the time of ovulation. So, eventually, one follicle becomes dominant. The maturing egg inside the dominant follicle releases more and more estrogen, which in turn eventually leads to a brief surge in luteinizing hormone, followed within 24 to 36 hours by (ta-da!) ovulation. After the ‘main event’ ends and the mature egg is released, the “leftovers” of the burst follicle form the corpus luteum.
Where does the corpus luteum come from, and what does it do?
The corpus luteum forms at the ends of the burst follicle, and it is made of two kinds of follicular cells: granulosa cells and theca cells. Size ranges from almost an inch to almost two inches across, and it is yellow in color (hence the name), which is due to the influence of lutein and lipids on the follicle.
So what does this floating yellow structure made up of a busted follicle actually do? Even though it’s role is temporary (more on this below), the corpus luteum produces important, powerful hormones, including the dominant hormone in the luteal phase (remember that the follicular phase comes first and the luteal phase comes second), which is progesterone. Who knew “leftovers” could be so important?
While the corpus luteum produces lots of progesterone, a little known fact is that it also produces at least three other hormones:
- Estrogen (the ‘yin’ to progesterone’s ‘yang’);
- Inhibin, which is a hormone necessary for proper regulation of follicle stimulating hormone (FSH) (which will be necessary when the follicular phase rolls back around); and
- Relaxin, a hormone that relaxes a pregnant woman’s body, particularly in the third trimester in preparation for labor and birth.
What’s more, there’s reason to believe there’s even more the corpus luteum does hormonally that we don’t yet understand [1].
What directs the actions of the corpus luteum?
In a woman who isn’t pregnant, luteinizing hormone (LH) “tells” the corpus luteum to produce progesterone, estrogen, and the rest. In a woman who is pregnant, large amounts of human chorionic gonadotropin (hCG) produced by trophoblastic cells (which will turn into the placenta) do the same thing [2][3].
Some women may have what is known as a luteal phase defect, which is when the corpus luteum doesn’t produce enough progesterone and/or estrogen, or when the uterine lining doesn’t respond appropriately to these hormones. If a woman has a luteal phase defect and is under the care of a restorative reproductive medicine (RRM) healthcare provider, she may be prescribed hCG, even when she’s not pregnant and isn’t trying to conceive. Given in a series of injections timed, as you might expect, with the luteal phase of a woman’s cycle, supplemental hcG can direct her body to make enough of these other important hormones, which are essential for regular cycles, optimal hormone levels, and the ability to conceive.
The corpus luteum is important for pregnancy
As you may now have guessed, a healthy corpus luteum is also essential for the maintenance of a new pregnancy. The hormones it produces essentially ensure a secure, healthy environment in the womb (the uterus) for the baby, specifically through the endometrium-strengthening and stabilizing effects of progesterone. Even though the corpus luteum is located inside the ovary, it works its magic (via progesterone, and in a lesser way through estrogen) inside the uterus.
Why should I care if I’m not pregnant or trying to get pregnant?
Without a healthy corpus luteum, also known as having a luteal phase defect, you won’t have adequate progesterone levels during your luteal phase. Low progesterone is connected to many reproductive health problems, ranging from premenstrual syndrome to infertility to miscarriage. (We previously covered potential luteal phase defect causes, how to know you might have one, and how to get help here.)
How long does the corpus luteum stick around?
It all depends, and this is what’s so fascinating. Your body makes a new corpus luteum every time you ovulate, so it’s just a temporary hormone producer. If you don’t get pregnant, the corpus luteum breaks down within two weeks after you ovulate, and becomes a scar known as the corpus albicans (white body) [4] .
But if you do get pregnant, even in its very earliest stages, your baby’s body and the trophoblast (which develops into the placenta) rapidly release hCG in exponentially greater amounts. More hCG tells your body to make more progesterone. Around twelve weeks gestation, when the placenta takes over progesterone production, the corpus luteum has served its purpose and shrivels up and eventually reabsorbs. (By the way, if you’re pregnant and your healthcare provider mentions that they see a corpus luteum cyst during an ultrasound, no need to worry. More on them here, but they are “harmless, painless, and usually go away without treatment” according to the Cleveland Clinic.)
“Corpus luteum” is a term every woman should know
Sure, the corpus luteum matters most during pregnancy. Still, this small but mighty, here-today-and-gone-in-two-weeks organ matters for every woman because of its impact on luteal phase (and overall cycle) health.
References:
[1] Gibson, M, Glob. libr. women’s med., International Federation of Gynecology and Obstetrics. (2008) (ISSN: 1756-2228); DOI 10.3843/GLOWM.10291 accessed 9/21/2022. [2] Nedresky D, Singh G. Physiology, Luteinizing Hormone. [Updated 2021 Sep 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK539692/ [3] Betz D, Fane K. Human Chorionic Gonadotropin. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532950/[4] Oliver R, Pillarisetty LS. Anatomy, Abdomen and Pelvis, Ovary Corpus Luteum. 2021 Oct 30. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30969526.Additional Reading:
FAM Basics: What is the luteal phase of the menstrual cycle?
