Vaginal progesterone vs. 17-OHPC
Although a 2017 meta-analysis had found vaginal progesterone to be superior to 17-OHPC in preventing preterm birth, few studies were available, and they had wide confidence intervals. This open-label randomized controlled trial took place at five U.S. sites and included participants who had a singleton pregnancy less than 24 weeks along and a history of singleton preterm birth between 16 and 37 weeks. The trials excluded those with placenta previa or accreta, preterm labor, preterm premature rupture of the membranes, clinical chorioamnionitis, or a major fetal anomaly or chromosomal disorder.
Among 205 women initially randomized, 94 in each group completed the trial, either inserting 200 mg of micronized progesterone daily with a vaginal suppository or receiving 250 mg of weekly intramuscular injections of 17-OHPC from 16 to 36 weeks’ gestation. The only significant difference between the groups in demographics or clinical features was that the vaginal progesterone group had a higher proportion of multiple past preterm births (33%) compared with the 17-OHPC group (17%). Cervical length and use of cerclage were also similar between the groups.
Though 30.9% of the vaginal progesterone group delivered preterm before 37 weeks, compared with 38.3% in the 17-OHPC group, the difference was not significant (P =.28). There was a borderline statistical difference between gestational age at delivery: 37.4 weeks in the vaginal progesterone group versus 36.3 weeks in the 17-OHPC group (P =.047). Neonatal outcomes were clinically similar between the two groups. Therapy initiation did slightly differ between the groups, with an average start 1 gestational week earlier in the vaginal progesterone group (16.9 vs. 17.8, P =.001) and a higher proportion of patients in the 17-OHPC group initiating therapy after 20 weeks (16.5% vs. 2.2%, P =.001). Adherence was otherwise similar between the groups, and the groups reported similar rates and types of side effects.
The trial did not meet the primary endpoint of vaginal progesterone reducing risk of recurrent preterm birth by 50%, compared with 17-OHPC, but it may increase latency to delivery, Rupsa C. Boelig, MD, of Thomas Jefferson University, Philadelphia, told attendees. Though this was the largest trial to compare vaginal progesterone with 17-OHPC for preventing preterm birth, it was underpowered to detect a difference in efficacy, to conduct subgroup analyses, and to assess secondary outcomes, Dr. Boelig noted. “Baseline difference in preterm birth risk may affect apparent relative efficacy of vaginal progesterone.”
Nevertheless, the “totality of evidence appears to be greater for vaginal progesterone,” Dr. Boelig said, making vaginal progesterone an acceptable alternative to 17-OHPC. ACOG recommendations currently include offering either, but SMFM recommendations only mention 17-OHPC.
Dr. Jenny Mei
It’s worth noting, however, that the future of 17-OHPC, a synthetic compound, compared with naturally occurring micronized progesterone, continues to be uncertain following a 2020 study that found no evidence of its efficacy, leading the Food and Drug Administration to withdraw its approval for prevention of preterm birth. ”These findings are important especially in light of the controversy surrounding 17-OHP,” Jenny Mei, MD, a maternal-fetal medicine fellow at UCLA, said in an interview after attending the presentation. “It is also sometimes difficult for patients to commit to weekly 17-OHPC injections, which requires time and many doctors visits, as compared to vaginal progesterone, which patients can administer at home.” Since this study does not have a placebo group, “it does not address the question of the overall efficacy of either medication compared to a control,” Dr. Mei said. ”It is also a somewhat small patient population so the results may change with a larger population. The authors conclude it is worth readdressing the use of vaginal progesterone for these patients.”
Dr. Herman Hedriana
Herman L. Hedriana, MD, professor and director of the division of maternal-fetal medicine and the maternal-fetal medicine fellowship program at the University of California, Davis, also pointed out notable differences between the two compounds.
“One has to remember that the formulation and mechanism of action are very different between 17-OHPC and the vaginal application of micronized progesterone. We do not have enough data to say one is superior versus the other,” said Dr. Hedriana, who was not involved in the research. “With 17-OHPC, the mechanism of action appears to be influenced by how the drug is metabolized based on race and ethnicity makeup, and may be influence by epigenetics,” while the mechanism for vaginal progesterone is probably local “given it is applied directly next to the cervix; hence, the results are it is effective in short cervices.” But those differing mechanisms don’t change the clinical significance of the findings. “One can use vaginal progesterone or 17-OHPC based on patient preference and availability,” Dr. Hedriana said.
The researchers of both studies reported no personal financial or industry disclosures, though Dr. Boelig disclosed that she had taken 17-OHPC and had cerclages during both her pregnancies, which resulted in healthy children today. The PREEMPT trial was funded by the Canadian Institutes of Health Research. The head-to-head trial was funded by the National Institute of Child Health and Development, the March of Dimes, the EW Thrasher Foundation, the PhRMA Foundation, and Covis Pharma, who manufactures the 17-OHPC drug Makena.
This story was updated on 2/8/2022.