The effectiveness of vaginal progesterone to prevent preterm birth in singleton pregnant women with a short cervix at 18-32 weeks gestation.

Short cervix is a risk factor for preterm birth. Currently, both international and domestic studies about progesterone's effectiveness are limited to pregnant women at 18-24 weeks gestation. However, multiple studies indicated that cervical length was associated with preterm birth even before 32 weeks of gestation. Therefore, this study expanded the gestational week range to investigate whether progesterone can reduce the rate of preterm birth in singleton pregnant women with a short cervix at 18-32 weeks gestation.
Pregnant women who underwent prenatal examination at Peking University First Hospital from January 2016 to August 2020 were prospectively followed. A total of 132 asymptomatic singleton pregnant women at 18-32 weeks gestation with a cervical length <25 mm were ultimately enrolled. According to the method of treatment, the participants were divided into progesterone group (80 patients) and control group (52 patients). The rate of preterm birth (PTB) at different stages was compared between two groups.
(1) There was no significant difference in the total preterm birth rate (18.8% vs. 21.2%, RR 0.886[0.442-1.777], p  = 0.734). (2) Stratified analysis found that, for pregnant women at <24 weeks gestation, there was a significant difference in the rate of PTB at <32 weeks (2.8% vs. 33.3%, p  = 0.021). For women at 24-28weeks gestation, significant difference was not found in the rate of PTB at <37 weeks gestation (25% vs. 42.9%, RR = 0.583[0.186-1.831], p  = 0.682), neither for women at after 28 weeks(12.5% vs. 11.1%,1.12[0.27-4.59], p  = 1). (3) Vaginal progesterone was not associated with low birth weight (13.8% vs. 19.2%, p  = 0.4), or preterm birth-related complications such as respiratory distress syndrome (3.8% vs. 7.7%, p  = 0.555), aspiration pneumonia (22.5% vs. 19.2%, p  = 0.653) and sepsis (2.5% vs. 7.7%, p  = 0.331).
For pregnant women with a short cervix at 18-24 weeks gestation, the rate of preterm birth before 32 weeks could be significantly reduced. For women with a short cervix at 24-28 weeks gestation, the rate of preterm birth could be reduced, while there was no significant effect for pregnant women. Further studies with a larger sample size and randomized controlled researches are needed.