Progesterone appears to protect some women from preterm birth

Researchers report that, among pregnant women with a short cervix at around 20 weeks, treatment with the hormone progesterone achieves a better result at reducing the risk of severe preterm birth than treatment with a cervical pessary.

The findings were published in the BMJ on March 12, 2024.

“This is an important improvement that can contribute to the reduction of preterm births and the associated complications, such as an increased risk of infant mortality and long-term health problems for the child,” said investigator Eva Pajkrt, MD, professor of obstetrics at the University of Amsterdam’s Faculty of Medicine (AMC-UvA) in Amsterdam, the Netherlands.

As background, the authors noted, “Preterm birth, defined as birth prior to 37 weeks, remains a serious problem with far-reaching consequences. Approximately 13.5 million children worldwide are born preterm each year. Children who are born preterm are at higher risk for, both physical and developmental, lifelong complications.”

The objective of this new study was to compare cervical pessary treatment and vaginal progesterone treatment in the prevention of adverse perinatal outcomes and preterm birth in women with singleton pregnancies and with no prior spontaneous preterm birth at less than 34 weeks’ gestation.

Eligible subjects had a short cervix of 35 mm or less.

The study open label and randomized. It took place at 20 hospitals and five obstetric ultrasound practices in the Netherlands.

From July 1, 2014 to March 31, 2022, 635 subjects were randomized to pessary (n=315) or to progesterone (n=320), with 612 were included in the final analysis.

The composite adverse perinatal outcome occurred in 19 (6%) of 303 subjects with a pessary versus 17 (6%) of 309 subjects in the progesterone group.

But, notably, in the subgroup of cervical length of 25 mm or less, spontaneous preterm birth at less than 28 weeks occurred more often after pessary than after progesterone (10/62 (16%) vs 3/69 (4%), with a 370% greater relative risk. And adverse perinatal outcomes appeared more often in the pessary group (15/62 (24%) vs 8/69 (12%) in the progesterone group, with a greater relative risk of 210%.

The authors concluded, “In women with a singleton pregnancy with no prior spontaneous preterm birth at less than 34 weeks’ gestation and with a mid-trimester short cervix of 35 mm or less, pessary is not better than vaginal progesterone. In the subgroup of a cervical length of 25 mm or less, a pessary seemed less effective in preventing adverse outcomes. Overall, for women with single baby pregnancies, a short cervix, and no prior spontaneous preterm birth less than 34 weeks’ gestation, superiority of a cervical pessary compared with vaginal progesterone to prevent preterm birth and consecutive adverse  outcomes could not be proven.”