Progesterone and premature birth: What a new study means for pregnant women
December 20, 2022
A study published by UT Southwestern in October 2022 adds to a growing body of research suggesting that vaginal progesterone might only help prevent preterm birth in specific cases – and comes on the heels of removal of a progesterone drug from the market.
Preterm birth – delivery before 37 weeks of pregnancy – is a significant problem in the U.S. The number of preterm births in the country rose to 10.5% in 2021, a 4% increase over 2020. In Texas the number is higher, with 11.4% of babies being born preterm.
Approximately 66% of infant deaths occur among babies born prematurely. Babies who survive are at increased risk for health issues such as breathing problems, feeding difficulties, cerebral palsy, developmental delays, and vision and hearing problems.
Previous research shows that the hormone progesterone can help stop the uterus from contracting too soon, and vaginal progesterone hormone treatment is prescribed for preventing preterm birth in patients with a short cervix – the area between the vagina and uterus – who are pregnant with a single baby.
There has been interest among providers in whether giving vaginal progesterone may help other pregnant patients also reduce the risk of early delivery. Our study suggest this might not be true.
In our study, 24% of women who took vaginal progesterone gave birth at or before 35 weeks, compared to 16.8% in control data from previous studies. This means that taking vaginal progesterone did not decrease the risk of preterm birth. Though the percentage was higher in the progesterone group, research does not show that taking progesterone increases the risk of premature birth.
There were some limitations to this study, and additional research will be needed before we completely stop using vaginal progesterone to help prevent preterm birth. Progesterone may be effective for patients who have a short cervix, which is a risk factor for preterm delivery.
But the new research does add to growing evidence that progesterone may not benefit some patients.
Growing research on progesterone and preterm birth
The causes of spontaneous preterm birth remain elusive. However, once a woman has one premature delivery from spontaneous labor or rupture of membranes (when a woman’s “water breaks”), the risk of having another is two to three times higher. And the earlier the first preterm birth, the higher the possibility of preterm birth in the next pregnancy.
A large 2003 study showed weekly progesterone (17-OHPC) injections given to pregnant women with a history of at least one prior preterm birth reduced the risk of delivery before 37 weeks by 34%.
In 2021, 11.4% of babies born in Texas were premature, slightly higher than the rate of 10.5% nationwide.
Based on these findings, the U.S. Food and Drug Administration (FDA) conditionally approved a drug called Makena for the prevention of recurrent preterm birth in women with a single-baby pregnancy and a history of preterm delivery. As a part of this process, a confirmatory study known as the PROLONG trial was performed.
PROLONG found that the rate of preterm birth was similar in women who received weekly progesterone injections and those who received placebo injections. This followed a 2017 study published by UT Southwestern researchers that also concluded progesterone injections did not reduce preterm birth, but they may increase the risk of a woman developing gestational diabetes.
Based on these studies, an FDA panel in October 2022 voted to withdraw Makena from the market.
We hope that these studies will continue to spur new research into progesterone and other potential treatments for preterm birth. But what do they mean for women right now who have had a spontaneous preterm birth due to early labor or rupture of membranes in the past?
What to do if you’ve had a premature birth
It’s important to note that we’re not talking about all progesterone treatments for recurrent preterm birth. For example, these studies do not affect the use of vaginal progesterone given to women at risk of premature delivery due to a short cervix.
Professional societies such as the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine are not yet changing current recommendations that support the use of vaginal progesterone.
If you’ve had a premature baby or complex pregnancy in the past, going into another pregnancy may cause you to feel stressed or anxious. It’s important to remember that what happened was not your fault – and just because it happened in one pregnancy doesn’t mean it’s certain to happen again.
To talk with a doctor about a current or planned pregnancy, call 214-645-8300 or request an appointment online.
