1. Among women with a sonographic short cervix, those randomized to receive daily vaginal progesterone were 45% less likely to experience preterm delivery prior to 33 weeks gestation (NNT=14).
2. Adverse neonatal outcomes including respiratory distress syndrome (NNT=22), low birthweight and neonatal mortality were significantly less common in the vaginal progesterone group.
Original date of publication: June 15, 2011
Study Rundown: Preterm delivery accounts for a significant proportion of neonatal morbidity and mortality. In the United States, over 12% of births are preterm. Preterm infants are more likely to experience respiratory distress syndrome, failure to thrive, low birthweight (birthweight <1500g), cerebral palsy and neonatal death. One of the more specific risk factors for preterm delivery is a sonographically short (10-20mm) cervix on second trimester ultrasound. Historically, however, clinicians have been unable to take advantage of this powerful predictor of preterm birth due to lack of an established intervention to improve clinical outcomes. Previous research has investigated the role of cervical cerclage, pessaries and progesterone administration in this setting. Prior investigations identify a decreased rate of preterm delivery with vaginal progesterone but none have demonstrated improved neonatal outcomes (see background reading).
This study evaluated the impact of daily vaginal progesterone on rate of preterm birth in women with a short cervix on second trimester (19+0- 23+6weeks) ultrasound. Results demonstrate that vaginal progesterone is associated with a decreased rate of preterm birth prior to 28, 33 and 35 weeks gestation. Adverse neonatal outcomes were significantly less incident among women on daily vaginal progesterone. Strengths include a parsimonious randomized, placebo-controlled design. A sample population of women receiving care at 44 delivery centers in 10 countries with analysis stratified by center increases applicability across practice settings without compromising validity. The study was underpowered to stratify analysis by history of prior preterm birth. Patients willing to participate in this study (e.g. elect to undergo study center visits every 2 weeks) may not be representative of all women with a midtrimester sonographically short cervix. This landmark study was the first to demonstrate improved neonatal outcomes with vaginal progesterone for sonograhically short cervix and thus changed practice recommendations for women with this risk factor for preterm birth.
Background reading: NEJM: Risk of preterm birth among women with short cervix
Dr. Alan Peaceman, MD, talks to 2 Minute Medicine: Northwestern University School of Medicine; Chief, Division of Obstetrics and Gynecology-Maternal Fetal Medicine.
“This study was the first to demonstrate improved neonatal outcomes with vaginal progesterone for a sonograhically short cervix. Findings identify a suitable intervention that significantly reduces the risk for preterm birth before 33 weeks gestation and changed practice recommendations for women with this risk factor for preterm birth.”
In Depth [Phase III randomized placebo-controlled trial]: Asymptomatic women with a singleton pregnancy and short (10-20mm) cervix on second trimester ultrasound were randomized to receive daily vaginal progesterone gel (n = 235) or placebo (n = 223) daily through delivery, term, or rupture of membranes (whichever came first). Women with a planned cerclage placement and those with acute cervical dilation were excluded. Intention-to-treat analysis assessed the incidences of preterm birth, distress syndrome, low birth weight (birthweight < 1500g) and a composite outcome of neonatal morbidity and mortality.
Compared to placebo, women taking vaginal progesterone were less likely to experience preterm birth before 33 weeks of gestation (RR: 0.52, CI: 0.31-0.91, NNT = 14). Women randomized to receive vaginal progesterone also experienced decreased risk of preterm birth before 28 weeks (Crude RR: 0.50, CI: 0.25-0.97) and before 35 weeks (Crude RR: 0.62, CI: 0.42-0.92). Rates of adverse perinatal outcomes, including respiratory distress, low birthweight and composite neonatal morbidity or mortality were also less common among women taking vaginal progesterone (p<0.05 for all, NNT for RDS=22). Incidences of treatment-related adverse events did not differ between groups (p = 0.59).
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