1. Among women taking 17 hydroxyprogesterone caproate (progesterone) injections, only those with BMI ≤30 kg/m2 were less likely to experience preterm birth.
2. Progesterone injections were associated with a decreased risk of preterm birth among women weighing ≤165 lbs.
Evidence Rating Level: 2 (Good)
Study Rundown: PTB complicates over 11% of deliveries in the U.S. and is a leading cause of neonatal morbidity and mortality. The strongest risk factor for PTB is a history of prior PTB. While it remains difficult in general to predict and prevent PTB, there is excellent data demonstrating benefit to progesterone injections for prevention of recurrent preterm birth. While 250mg of 17 hydroxyprogesterone caproate (17OHPc) is the standard administration dose, formal dosing studies have not been performed. Prior work suggested that serum 17OHPc levels are inversely related to BMI. This work identified a threshold serum level below which 17P was not as effective in reducing risk of PTB. In the present study, authors evaluated whether weight and BMI affected the efficacy of 17OHPc and found that in women with pre-pregnancy BMI >30 kg/m2 or pre-pregnancy weight >165 lbs, 17OHPc lost its protective effect.
Strengths of the study included randomized controlled design including prospectively collected exposure and outcome data. Limitations included post-hoc analysis, which may introduce errors due to multiple comparisons and self-reported anthropometric measurements, which might confound results. Further evaluation of appropriate dosing of 17OHPc is merited to improve counseling and management of overweight and obese pregnant women with a history of prior preterm birth.
In-Depth [randomized controlled trial]: This secondary analysis evaluated the influence of maternal weight and BMI on effectiveness of 17OHPc in preventing recurrent preterm delivery (<37 weeks gestation) in women with a history of prior spontaneous preterm birth. Women were randomized to receive 17OHPc (n = 294) or placebo (n = 149) starting in the 2nd trimester. The primary outcome of interest was delivery <37 weeks gestation.
Women with BMI ≤30 kg/m2 randomized to 17OHPc injections were less likely to deliver before 37 weeks (RR 0.54, CI 0.41-0.71 for BMI <25 kg/m2 and RR 0.55, CI 0.36-0.83 for BMI 25-30 kg/m2) compared to women randomized to placebo. Among women with BMI >30kg/m2, those receiving 17OHPc did not experience a reduced risk for recurrent preterm delivery compared to placebo. Overall, 17OHPc was found to be associated with a reduced risk of PTB only among women weighing ≤165 lbs.
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