Do progesterone supplements reduce miscarriage?

This review looked at whether progesterone supplements reduce miscarriage in women who have bleeding during pregnancy. It found that oral progesterone pills reduced miscarriage in these women.

Miscarriage is a concern for women who are pregnant or trying to conceive. Bleeding, pain or cramping during early pregnancy is a sign of threatened miscarriage. Up to half of the women with these symptoms will go on to have a miscarriage.

There are multiple factors that can contribute to miscarriage. Some miscarriages are due to poor support from the lining of the uterus. The uterus prepares for pregnancy in response to hormonal changes. Progesterone is a hormone that rises during the second half of the menstrual cycle and stays high throughout early pregnancy. If progesterone is artificially lowered, it can cause miscarriage. Despite past studies, it is unclear whether progesterone supplements can reduce miscarriage in women with bleeding during early pregnancy.

This review included data from ten trials with 5056 participants overall. All trials compared patients taking progesterone to those taking placebo (inactive comparison treatment) or no treatment.

Six trials recorded birth outcomes on 4790 patients (2411 progesterone + 2379 placebo). Overall, 72.9% of patients taking progesterone had a live birth, compared to 69.7% of patients not taking progesterone. Patients taking progesterone were 7% more likely to have a live birth. Oral progesterone pills significantly increased live birth rates by 17%. Patients taking vaginal progesterone suppositories were 4% more likely to have a live birth, but this difference could have been due to chance.

The miscarriage rate was 18.5% in patients taking progesterone, compared to 21.9% in patients not taking progesterone. Patients taking progesterone were 27% less likely to have a miscarriage compared to not taking progesterone.

There was no difference in preterm birth or birth defects between the two groups.

This review found that oral progesterone supplements increase birth rates in women with bleeding during early pregnancy.

There were differences between the studies which complicated combining data. Also, the authors were not able to test whether studies that found progesterone was not effective were less likely to be published (the publication bias).