The luteal phase of the menstrual cycle, explained

What is the luteal phase?

The luteal phase is the part of your menstrual cycle between ovulation (when your body releases an egg for fertilization) and the beginning of your next menstrual period.

If you're trying to get pregnant, you may know this phase as the "two week wait" before you miss a period and can take a pregnancy test. It can seem like an eternity if you're hoping for a baby, but the luteal phase is a busy time for your body as it prepares for a possible pregnancy.

It's called the luteal phase because the follicle that releases the egg becomes something called a corpus luteum, explains Sasha Hakman, M.D.Opens a new window, M.S., an ob-gyn and reproductive endocrinologist in Los Angeles and member of the BabyCenter Medical Advisory Board.

"The corpus luteum produces the main hormones needed to prepare for a potential pregnancy," Dr. Hakman says.  

During this phase of your cycle, the egg journeys down the fallopian tube, and the lining of the uterus prepares for pregnancy, thickening and growing blood vessels to support the embryo.

There's a lot going on hormonally during this period, too:

• Progesterone levels increase to help prepare the uterus for implantation. If the egg isn't fertilized or an embryo doesn't implant, your progesterone levels will gradually drop towards the end of this phase and you'll get your period. If an embryo implants, progesterone production will stay up and maybe even increase by the end of the luteal phase.
• Estrogen levels (which drop after ovulation) rise mid-luteal phase and then fall just before menstruation if there's no implanted embryo. Estrogen helps thicken the lining of the uterus before ovulation.
• If the egg is fertilized, and embryo development begins, you'll start producing human chorionic gonadotropin (hCG). HCG maintains the corpus luteum until around the 10th week of pregnancy, when the placenta takes over. (HCG is the hormone that's detected in a pregnancy test.)
• Luteinizing hormones (which stimulate ovulation) drop immediately after ovulation and remain low through the luteal phase.
• Follicle stimulating hormone (the hormone responsible for recruiting an egg for ovulation) remains low after ovulation but begins to rise right before the start of your period if you're not pregnant.  

How long is the luteal phase?

According to the American Society for Reproductive MedicineOpens a new window (ASRM), the luteal phase typically lasts about 12 to 14 days, though it may range from 11 to 17 days. If your menstrual cycle varies in length, it's usually the (earlier) follicular phase that changes.

Short luteal phase

A short luteal phase lasts less than 10 days. This is sometimes called luteal phase deficiency (LPD). There's some debate about the effects a short luteal phase might have on fertility, and the topic is being researched.

"It's still unknown whether LPD causes implantation failure or early pregnancy loss," says Dr. Hakman.

One theory is that in a short luteal phase, there isn't enough progesterone to adequately prepare the uterine lining for implantation. "Progesterone is responsible for making the lining sticky and causing the endometrium to secrete important substances for early pregnancy," Dr. Hakman explains.

We also don't know if diagnosing and treating LPD is useful. "Controversy exists regarding the multiple proposed measures for diagnosing LPD," explains ASRM, "and, assuming it can be diagnosed accurately, whether treatment improves outcomes."

Having a short luteal phase one month doesn't necessarily mean that you'll have a short one every month. But if it persists, says Dr. Hakman, it could be the result of a medical condition.

Many conditions have been linked to LPD, such as eating disorders and significant weight loss, stress, obesity, polycystic ovary syndrome (PCOS), endometriosis, hyperprolactinemia, and thyroid dysfunction. The luteal phase naturally shortens with age, usually beginning around age 37 or 38.

There's also some evidence that drinking moderate to heavy amounts of alcohol, especially during the luteal phase, could reduce the chances of conception.  And in one study of over 1,600 cycles published in Fertility and SterilityOpens a new window, significantly more women with a short luteal phase were smokers.

Long luteal phase

A long luteal phase is 18 days or longer. Sometimes a condition that causes a hormonal imbalance – such as polycystic ovary syndrome (PCOS) – can cause a long luteal phase.

If you don't get your period after 14 days, though, you might want to take a pregnancy test.

What luteal phase symptoms should I watch for?

Thanks to the production of progesterone, you may experience symptoms similar to those of premenstrual symptom (PMS) during the luteal phase, such as:

• fatigue
• bloating
• headaches
• breast tenderness
• skin breakouts
• changes in appetite
• mood swings

If you're tracking your basal body temperature (BBT), you'll see that your temperature stays elevated throughout the luteal phase.

You may notice less cervical mucus in the luteal phase, and it may be thick, dry, and cloudy rather than clear and thick like it was before ovulation.

Learn more:

• Low progesterone during pregnancy
• How often should you have sex to get pregnant?
• Pregnancy symptoms: 10 early signs of pregnancy