Low progesterone during pregnancy

What is progesterone?

Progesterone is a hormone that your body produces after ovulation. It prepares the lining of the uterus for pregnancy. Progesterone levels rise and fall every menstrual cycle. If you don't get pregnant, the progesterone decreases, and you menstruate.

If you do get pregnant, you continue producing progesterone, which keeps the uterine lining healthy and prevents your body from having contractions as the uterus grows. Progesterone also helps your body develop milk-producing glands in preparation for breastfeeding, and it plays a role in milk production after birth. Your levels of progesterone will increase through pregnancy.

Low progesterone is also known as a luteal deficiency. That's because the luteal phase of your menstrual cycle begins after ovulation, when progesterone production increases.

How low progesterone affects pregnancy

We're not sure how low progesterone affects pregnancy. Some experts say low progesterone has no impact, while others say that without adequate progesterone the uterus won't be prepared for pregnancy and the embryo won't be able to implant and thrive in the uterine lining.

We do know that women who have had a miscarriage tend to have lower levels of progesterone, though we don’t know whether the miscarriage caused the progesterone to drop or if the low progesterone contributed to the miscarriage.

What are low progesterone levels?

Progesterone levels are not something your caregiver will check during pregnancy. There is a wide range of normal, and numbers would fluctuate depending upon when your body released the hormone. Instead, progesterone supplementation during pregnancy would be based on risk factors, such as your history.

Your caregiver might check progesterone levels prior to pregnancy, if she had concerns about your menstrual cycles or whether or not you are ovulating, for example.

The normal ranges of progesterone are:

• Before ovulation: Less than 1 nanogram per milliliter (ng/mL)
• Mid menstrual cycle: 5 to 20 ng/mL
• First trimester of pregnancy: 11.2 to 90 ng/ml
• Second trimester of pregnancy: 25.6 to 89.4 ng/ml
• Third trimester: 48 to 150 to over 300 ng/ml

Note that different labs may use different ranges, so talk with your caregiver about your results.

Does low progesterone cause infertility?

Low progesterone by itself has not been proven to cause infertility, though may be linked to a number of possible contributing factors. It may cause failed implantation of the embryo, and women with low progesterone may have problems with their menstrual cycles, for example.

When tested during the menstrual cycle, low progesterone could be an indication of low ovulation or infertility.

Low progesterone causes

We don't know what causes low progesterone, but low levels may be linked to:

• A miscarriage or a threatened miscarriage
• An ectopic pregnancy
• Irregular or no menstrual periods

Low progesterone symptoms

Low progesterone symptoms may include:

• Irregular or no menstrual periods
• Headaches or migraines
• Mood changes
• Frequent miscarriages
• Spotting and abdominal pain during pregnancy

Keep in mind that reasons other than low progesterone may cause many of these symptoms.

Does low progesterone increase the chance of miscarriage?

Women who have experienced miscarriage tend to have lower levels of progesterone, but we don't know which causes which.

Studies have shown that women who have had the corpus luteum (the gland that produces progesterone) removed before 8 weeks of pregnancy had resulting miscarriages.

Do progesterone supplements help prevent miscarriage or preterm birth?

Researchers are working to determine whether progesterone supplements can help prevent miscarriage or preterm birth. There are conflicting findings. Here is some of what we know.

Prevention of miscarriage

One study of over 800 women did not find a significantly higher rate of live births among women with a history of unexplained recurrent miscarriages who were given progesterone therapy.

But other studies have suggested that progesterone supplements may help some women in specific circumstances, especially women who have had recurring miscarriages.

For example, one study of over 2,000 women in 14 trials showed no difference in the overall risk of miscarriage in women who were given progesterone and those who were given a placebo or no treatment. But the study did show that progesterone treatment decreased the miscarriage rate among women who had three or more consecutive miscarriages in the past.

Another study found small but positive effects from treating women who were having vaginal bleeding in early pregnancy and had previous miscarriages.

Reducing preterm birth

For women who have a shortened cervix (a sign of possible preterm birth) around 16 to 24 weeks of pregnancy, vaginal progesterone suppository or gel has been found effective for preventing preterm birth.

For women who have had one previous preterm birth prior to 36 weeks, progesterone supplementation during pregnancy was shown to reduce the risk of preterm birth. (A later study did not support this finding, but this later study had an insufficient sample size and was inconclusive about treatment.)

Note that progesterone treatment does not prevent premature labor in the case of twins or other multiples.

While the verdict is out on the efficacy of progesterone treatments, because they may help, and because the side effects are minimal, they are still routinely offered to some women in hopes of having a positive effect in preventing preterm birth and miscarriage.

Low progesterone treatments

If you have had repeated miscarriages and you have low progesterone levels, or if you have a history of preterm labor or a short cervix, your caregiver may treat you with a synthetic form of progesterone. You may also be given progesterone if you are undergoing IVF treatment.

Don't take over-the-counter progesterone suppositories or use over-the-counter progesterone creams. Your caregiver may prescribe one of three options:

• Progesterone injections (17P). To prevent premature labor, or for women receiving IVF, progesterone is sometimes given as a weekly shot.
• Vaginal progesterone gel or suppositories. This is another alternative for women undergoing IVF. It's also given to women with a "short cervix" (less than 2.5 centimeters, which may open early). These come with an applicator that looks like a tampon, and you apply it once or twice a day.
• Progesterone oral tablets. These may be given if you've had miscarriages in the past.

For women with a short cervix or history of preterm birth, treatment typically starts at 16 to 20 weeks of pregnancy and ends at 34 to 36 weeks.  For women taking progesterone because of recurrent miscarriages or because they are undergoing IVF, treatment starts after ovulation or as soon as the patient becomes pregnant and continues to about 8- to 10-weeks gestation.

Progesterone treatment has not been found useful for women carrying multiples, however.

In general, progesterone treatment is considered low risk, but each of these treatments has possible side effects, so be sure to discuss those with your caregiver.

Progesterone and ovulation are closely tied. You might be interested in learning more about ovulation symptoms (how to tell when you're ovulating) and using an ovulation test strip.

NOTE: This article was also reviewed by Erika New, M.D., a Reproductive Endocrinology and Infertility Fellow at the University of South Florida.

Learn more:

Basal body temperature and ovulation

Pinpointing a fertility problem

How to get pregnant fast