Taking progesterone does not cause miscarriage. Progesterone is the hormone your body naturally produces to sustain a pregnancy, and supplemental progesterone is specifically prescribed to help prevent pregnancy loss. No clinical trial has found that progesterone supplementation increases the risk of miscarriage. However, there is one important nuance worth understanding: progesterone can mask the symptoms of a miscarriage that is already happening, which can delay the diagnosis.
What Progesterone Does in Pregnancy
Progesterone is essential for pregnancy from the very start. It prepares the tissue lining of the uterus to allow a fertilized egg to implant, and it stimulates glands in that lining to secrete nutrients for the early embryo. Without enough progesterone, the uterine lining can break down, making it impossible for a pregnancy to continue.
Because low progesterone has long been suspected as a contributing factor in some miscarriages, doctors prescribe supplemental progesterone in early pregnancy. The goal is to support the uterine environment during the critical first trimester, when most pregnancy losses occur. This is especially common for women who have experienced previous miscarriages or who are bleeding in early pregnancy.
What the Largest Trials Found
Two major randomized trials have tested whether progesterone actually helps, and both provide reassurance that it does not cause harm.
The PRISM trial, the largest of its kind, enrolled over 4,000 women experiencing early pregnancy bleeding. The live birth rate was 75% in the progesterone group compared to 72% in the placebo group. For women who had also experienced one or more previous miscarriages, the benefit was clearer: 75% live births with progesterone versus 70% with placebo. The strongest effect appeared in women with three or more prior miscarriages, where progesterone raised the live birth rate from 57% to 72%.
The PROMISE trial focused specifically on women with a history of unexplained recurrent miscarriages. Published in the New England Journal of Medicine, it found a live birth rate of 65.8% in the progesterone group versus 63.3% in the placebo group. That difference was not statistically significant, meaning progesterone didn’t dramatically improve outcomes for this group, but it certainly didn’t worsen them either.
A Cochrane review pooling data from 10 trials and nearly 1,700 women reached a similar conclusion: progesterone supplementation may reduce the miscarriage rate compared to placebo, with no increase in stillbirths, neonatal deaths, or fetal abnormalities.
Why People Worry Progesterone Causes Miscarriage
This concern typically comes from one of two situations. The first is a theoretical one that researchers have acknowledged: if a pregnancy is non-viable due to a genetic abnormality in the embryo, progesterone’s uterine-relaxing properties could theoretically delay the body’s natural process of ending that pregnancy. This isn’t the same as causing a miscarriage. It’s the possibility that progesterone could briefly sustain a pregnancy that was already destined to fail. In practice, clinical trials have not shown this to be a meaningful problem.
The second and more common source of confusion is timing. Many women are prescribed progesterone because they are already at higher risk of miscarriage, whether due to bleeding or a history of losses. When a miscarriage happens despite treatment, it can feel like the progesterone caused it. But the miscarriage rate in these high-risk groups remains substantial even with treatment, and progesterone either lowers or has no effect on that rate. It does not raise it.
How Progesterone Can Mask Miscarriage Symptoms
This is the most practically important thing to understand. Progesterone supports the uterine lining and can suppress bleeding and cramping. If a pregnancy stops developing while you’re taking progesterone, you may not experience the typical physical signs of miscarriage, like heavy bleeding or strong cramps. Cambridge University Hospitals explicitly notes that taking progesterone may result in a delayed diagnosis of miscarriage because you may not have any symptoms.
This is why doctors typically schedule early ultrasounds for women on progesterone therapy. An ultrasound can confirm whether a pregnancy is developing normally regardless of symptoms. If you’re taking progesterone and something feels off, or if you simply want reassurance, an ultrasound is the most reliable way to check on the pregnancy’s progress.
What Happens When You Stop Taking Progesterone
Some women worry that stopping progesterone will trigger a miscarriage. When you stop taking any hormonal medication, the drop in hormone levels can cause withdrawal bleeding, which typically starts within a few days and lasts four to seven days. This bleeding is usually lighter than a normal period.
In a healthy, ongoing pregnancy, your placenta takes over progesterone production around weeks 8 to 12. Most doctors taper progesterone off around the end of the first trimester for this reason. If the placenta is functioning normally by that point, stopping supplemental progesterone will not cause a miscarriage because your body is already making enough on its own. Your doctor will time the discontinuation based on how far along you are and your individual risk factors.
Side Effects to Expect
Progesterone supplements, particularly vaginal pessaries, come with side effects that can be uncomfortable but are not signs of miscarriage. Common effects include drowsiness, stomach discomfort, and breast pain. If you’re using vaginal or rectal forms, you might also experience diarrhea, rectal soreness, gas, or leakage after the pessary dissolves. These are normal and don’t indicate anything is wrong with the pregnancy.
The overlap between progesterone side effects and early pregnancy symptoms (nausea, breast tenderness, fatigue) can make it hard to tell what’s causing what. Bleeding or severe cramping, on the other hand, are not typical side effects of progesterone and warrant a call to your provider. The key distinction is that progesterone side effects tend to be mild and systemic (drowsiness, bloating, breast soreness), while miscarriage symptoms are localized and more intense (heavy vaginal bleeding, rhythmic cramping in the lower abdomen).
Long-Term Safety for the Baby
A systematic review examining the long-term effects of prenatal progesterone on children found no significant differences in congenital malformations, chromosomal anomalies, or genital abnormalities between children exposed to progesterone in the womb and those who were not. One study did observe slightly higher rates of minor kidney, gastrointestinal, and respiratory issues in the progesterone group, but these occurred at very low frequencies (1 to 2% of children). No evidence of long-term harm was found from first-trimester use specifically. Hearing outcomes were actually slightly better in the progesterone-exposed group in one study, though the numbers were small.