Although there is a biological basis for it, there is scarce evidence on the effect of heparin in ameliorating placental insufficiency and maximizing gestational age at delivery among fetal growth restriction (FGR) pregnancies. To explore the effectiveness of treatment using low molecular weight heparin (LMWH) at a prophylactic dose started at the time of diagnosis in prolonging gestation in pregnancies with early-onset fetal growth restriction (FGR). This was a phase III, multicenter, triple-blind, parallel-arm randomized clinical trial conducted in two university hospitals in Spain. Singleton pregnancies qualifying for early-onset placental FGR according to the adapted Delphi consensus (20+0-31+6 weeks at diagnosis with umbilical artery Doppler with absent/reversed diastolic flow; or estimated fetal weight <10th percentile plus pulsatility index (PI) of umbilical artery Doppler >95th percentile; or estimated fetal weight <10th percentile plus mean PI of uterine artery Doppler >95th) were randomized to receive either subcutaneous treatment with bemiparin 3500 IU/0.2 mL/day or a placebo from inclusion at diagnosis to the time of delivery. The primary outcomes were prolongation of pregnancy from inclusion to live birth (days) and gestational age at live birth (days). 49 patients were included (23 in the LMWH group and 26 in the placebo group). In the LMWH group, the median prolongation of pregnancy was 42 days, while in the placebo group it was 41.5 days (median difference 0.5 days [95% CI -22.7 to 6.3] (p=0.667) and in the LMWH group, the median gestational age at delivery was 35.1 weeks, while in the placebo group, it was 34.6 weeks (median difference 0.5 weeks [95% CI -3.4 to 1.2] (p=0.639). The use of prophylactic dose LMWH started at the time of diagnosis does not prolong pregnancy in individuals with early-onset fetal restriction.
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