What Is the Corpus Luteum?

One of the most incredible things about being human is our ability to adapt, grow, and change throughout our lives. There are some things we tend to think of as pretty stagnant though – like our organs.

Heart, liver, kidneys, and even ovaries. These organs stay the same more or less as long as health issues don’t present themselves. But the female body has an organ that disappears and reappears with each menstrual cycle. 

We present… the corpus luteum.

It sounds like a cool band name but it’s actually an organ that’s essential for female reproductive health. Let’s learn more about it!

What Is the Corpus Luteum?

We mentioned before that the corpus luteum is a temporary organ, but how does that work? Ovarian cyst seems like a scary term, especially when talking about reproductive organs, but that’s what the corpus luteum starts as. Cyst in this context simply means a group of cells. 

The corpus luteum’s main role is to produce and release the hormones estrogen and progesterone, preparing the body for a potential pregnancy. It can be anywhere from 2 to 5 centimeters, but how does it form?

Typically there is one dominant follicle in the ovaries each ovulation cycle. This is a tiny sac that holds the developing egg. The sac then breaks during ovulation, allowing the egg to escape. A mass of cells (follicular granulosa and follicular theca cells) starts to form where the follicle was and begins to form into the corpus luteum.

Corpus Luteum and The Menstrual Cycle

About two weeks into the menstrual cycle, ovulation occurs. This is when the ovaries release an egg to be fertilized. It’s also the same time the corpus luteum forms. 

After ovulation is the luteal phase of the menstrual cycle, which is when the body prepares for a potential pregnancy by thickening the lining of the uterus.

Most ovulation cycles do not result in a pregnancy. Typically they lead back to the first stage of the menstrual cycle – your period. Without fertilization, the corpus luteum begins to break down about 10 days after ovulation. When this happens, the uterine lining that started to build up to prepare for pregnancy instead starts to shed – aka your period. 

Progesterone and Pregnancy 

If you do happen to get pregnant, the corpus luteum sticks around for a little longer – until about 12 weeks gestation. After that, the placenta (another temporary organ during pregnancy) takes over the role of progesterone production, and the corpus luteum starts to break down and get smaller.

So why is progesterone so important during pregnancy? This vital hormone makes it possible for a fetus to grow in the uterus. It first does this by making the uterus bigger. It also makes it possible for a fertilized egg to implant itself in the uterus by thickening the endometrium, or lining of the uterus. Progesterone is essential for keeping the uterine environment healthy by supplying the uterus with oxygen and blood so that the fetus can develop and grow. 

Later on in pregnancy progesterone also helps to prevent early labor by keeping the uterus from contracting before it needs to. It even helps prepare the body for lactation!

Corpus Luteum Disorders

Back to the corpus luteum. Just like any organ, some conditions can affect the health and function of the corpus luteum.

Cysts

One of the most common issues with the corpus luteum are cysts. These occur when the organ keeps growing instead of breaking down, causing it to fill with fluid.

While they typically disappear on their own, they can cause potential symptoms like:

• Lower back and body pain
• Irregular spotting
• Bloating
• Breast tenderness
• Pain when urinating or pooping
• Pelvic pain
• Pain during intercourse

Corpus Luteum Defect

Another potential issue is called corpus luteum defect, or luteal phase deficiency (LDP). This disorder was first pinpointed in 1949 and is a broad term for an abnormal luteal phase. 

Luteal phase deficiency typically leads to an abnormal length of the luteal phase or one that lasts less than 10 days. It may also be diagnosed by low progesterone levels across the luteal phase. Progesterone phase defect may contribute to infertility and miscarriage. We know the importance of the corpus luteum in early pregnancy because the removal of it can result in spontaneous pregnancy loss. 

Corpus luteum defect is directly linked to human chorionic gonadotropin (hCG) levels. When hCG levels don’t increase, it results in corpus luteum failure and a drop in progesterone levels. LDP may be a contributing factor in people who experience recurrent pregnancy loss. 

Luteal phase defect can be diagnosed using a few different methods:

• Measuring serum progesterone levels.
• Performing an endometrial biopsy.
• Determining luteal phase based on the length of the menstrual cycle.
• Determining luteal phase length based on basal body temperature.

Treatment for luteal phase defect may be as simple as lifestyle changes like stress management, physical activity, and diet change. Other cases may require hormonal treatment with progesterone, hCG, or a medication called clomiphene citrate. 

Corpus Luteum Overview

The corpus luteum is a vital organ for female reproduction. A new one grows each menstrual cycle after ovulation and sticks around in the event of pregnancy. Without pregnancy, the corpus luteum breaks down and leads to your period.

Issues with the corpus luteum may contribute to irregular menstrual cycles and fertility problems. This incredible organ is essential for fertility, menstruation, and pregnancy!