The Mystery and Importance of the Luteal Phase

How Long Should It Be? What Is Too Short? What Is a Luteal Phase Defect?

Woman with her hand on your abdomen having cramping during the luteal phase
Some women mistake luteal phase symptoms for early pregnancy signs. Frederic Cirou/PhotoAlto Agency RF Collections/Getty Images

The luteal phase is the portion of your menstrual cycle that occurs after ovulation but before the first day of your next menstrual cycle. On average, this phase lasts from 12 to 14 days.

Some people who menstruate and who have fertility problems experience a short luteal phase. Recurrent miscarriage (miscarrying two or more times in a row) has also been associated with a luteal phase that is shorter than normal.

When problems occur during the luteal phase it is sometimes referred to as a luteal phase defect. However, some people have a short luteal phase and normal fertility, making the possible connection between luteal phase length and fertility unclear.

What Is the Luteal Phase?

The menstrual cycle can be split into two parts: the follicular phase and the luteal phase.

The follicular phase is all about ovulation. Hormones trigger changes in ovarian follicles until a mature egg is ovulated. Follicles are small sacs in which the eggs of the ovaries develop. The scientific name for egg development and maturation is oogenesis.

The luteal phase is all about preparing the endometrium and body for pregnancy.

Your body is optimistic and assumes that the ovulated egg was fertilized. After ovulation, the follicle that released the egg becomes a corpus luteum. The corpus luteum secretes estrogen and progesterone.

While estrogen is important, progesterone might be the most important hormone during the luteal phase. Progesterone has many roles in the body, including:

  • Preparing the endometrium. Progesterone triggers the uterine lining (or endometrium) to thicken and prepare for embryo implantation.
  • Preventing menstruation. Progesterone stops the endometrium from breaking down (which could lead to miscarriage if you’re pregnant)
  • Suppressing GnRH, FSH, and LH. These hormones stimulate the ovaries and cause ovulation (if this did not happen, you might conceive again after you already were pregnant).

Progesterone also causes your body temperature to rise. If you chart your basal body temperature, you’ll notice a slight rise in temperature after ovulation.

If you get pregnant, your temperature will stay elevated beyond your regular luteal phase length. If you don’t get pregnant, your temperature will start to drop just before your period arrives.

The drop in progesterone levels both lowers your body temperature and starts menstruation. Progesterone is also responsible for symptoms during the luteal phase (which can be confused for early pregnancy signs).

Duration

On average, the luteal phase is between 12 and 14 days. However, it can be as short as 8 days and as long as 16 days. Whatever your regular luteal phase length is, it tends to be a consistent length every cycle.

For example, suppose that your luteal phase tends to be 12 days. You can count on it always being 11 to 13 days long. Then, if your luteal phase were to go longer than 13 days, it could be an early sign of pregnancy.

A luteal phase shorter than 8 (or 10) days can sometimes indicate a potential fertility problem, but not always. People who struggle to conceive or who have experienced repeated miscarriage might tend toward having shorter luteal phases, but it's also possible to have a short luteal phase without any fertility issues.

Don't immediately worry if you notice a short luteal phase when you are basal body temperature charting. If you do not have any other signs or symptoms of infertility, a short phase could be normal for you.

However, if you don’t get pregnant after one year of trying to conceive (or after six months, if you’re 35 years of age or older), talk to your doctor. You should also see your doctor if you have any other worrisome symptoms.

Luteal Phase Defect

A luteal phase defect is defined as having low or inadequate levels of progesterone during the luteal phase. It is a theoretical cause of infertility and early miscarriage, but there’s a lot of debate and controversy surrounding the diagnosis.

The American Society for Reproductive Medicine's position on luteal phase defects is that the condition does not exist as a standalone cause of infertility.

The reasons for the controversy include:

  • Diagnosis difficulties. Research has not found a definitive way to test or confirm a luteal phase defect.
  • Unclear outcomes. A short luteal phase or low progesterone level does not always cause infertility or repeat miscarriage.
  • Uncertain treatment outcomes. It’s unclear if proposed treatments improve fertility or can prevent miscarriage.

Possible symptoms associated with a luteal phase defect include:

Possible causes of a luteal phase defect include:

Diagnosis of a Luteal Phase Defect

There is no research-based way to diagnose a luteal phase defect. Every method has possible problems, but there are a few ways the defect might be detected.

Basal Body Temperature (BBT) Charting

Charting your basal body temperature might show an abnormally short luteal phase, but the method has caveats. Research has found that the exact day of ovulation is not always accurately indicated on a BBT chart.

Therefore, you could not be certain how many days your luteal phase is (it could be e longer or shorter than the chart indicates).

Progesterone Level Testing

While you could have your progesterone levels tested six to eight days after ovulation, the levels of progesterone that should be considered "normal" are unclear.

Another potential problem is timing. While progesterone levels peak about a week after ovulation, knowing exactly which day ovulation occurred is not always simple. If you don't know when ovulation occurred, you won't know when to test.

Endometrial Biopsy

An endometrial biopsy involves looking at endometrial tissue during the luteal phase and evaluating whether the cells look like they are in the correct stage of growth (in relation to where you are in your menstrual cycle).

While the method used to be considered the "gold standard" for diagnosing a luteal phase defect, studies have produced inconsistent results. For example, results that were considered abnormal did not necessarily lead to poor pregnancy results.

Luteal Phase and Early Miscarriage

Can a luteal phase defect cause early miscarriage? If so, can treating a luteal phase defect with progesterone solve the problem? For those who maintain that a luteal phase defect may not exist, the answer would be no. However, the answer (and the real question) might be more complicated than that.

There is not sufficient evidence to support the theory that a luteal phase defect (defined as a short luteal phase or low progesterone) alone will cause miscarriage or infertility. 

For women who have not had repeated miscarriages, studies have found that progesterone supplementation does not reduce the general risk of miscarriage in women.

However, recent studies have indicated that some women who have experienced repeat miscarriages (defined as two or more miscarriages in a row) might benefit from progesterone supplementation. The benefits of supplementation seem to be more likely if a woman has experienced three or more miscarriages in a row.

Treatment for a Luteal Phase Defect

Effective treatment for luteal phase defect is not clear. That said, you should bring any concerns you have about your menstrual cycle to your doctor. They might want you to try certain treatments, including:

  • Address underlying conditions. For example, if you have a thyroid condition it could affect your menstrual cycle and fertility. Your doctor would want to start by treating any condition that could be causing problems with your periods or fertility.
  • Boost ovulation with fertility drugs. This treatment can strengthen the corpus luteum and could lead to a healthier luteal phase.
  • Progesterone supplementation. This treatment is highly controversial, as it is not clear whether progesterone supplements can improve fertility or reduce early miscarriage. Research has indicated that supplemental progesterone might be beneficial for women who have had three or more miscarriages.
  • hCG injections. Low doses of hCG (an injectable fertility drug) can be given through the luteal phase, but progesterone supplementation is more common and has fewer side effects.

Your doctor might prescribe progesterone injections or progesterone suppositories if you are undergoing IVF treatment. Progesterone supplementation has been shown to improve the luteal phase and improve pregnancy outcomes with IVF.

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  2. Saccone G, Schoen C, Franasiak JM, Scott RT, Berghella V. Supplementation with progestogens in the first trimester of pregnancy to prevent miscarriage in women with unexplained recurrent miscarriage: a systematic review and meta-analysis of randomized, controlled trials. Fertil Steril. 2017;107(2):430-438.e3. doi:10.1016/j.fertnstert.2016.10.031

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