Low-molecular-weight heparin for women with unexplained recurrent pregnancy loss: a multicenter trial with a minimization randomization scheme

Ann Intern Med. 2015 May 5;162(9):601-9. doi: 10.7326/M14-2062.


Background: A daily injection of low-molecular-weight heparin (LMWH) is often prescribed to women with unexplained recurrent pregnancy loss (RPL), although evidence suggesting a benefit is questionable.

Objective: To determine whether LMWH increases ongoing pregnancy and live-birth rates in women with unexplained RPL.

Design: Controlled, multicenter trial with randomization using minimization conducted from 2006 to 2013. (ClinicalTrials.gov: NCT00400387).

Setting: 14 university hospitals and perinatal care centers in Germany and Austria.

Patients: 449 women with at least 2 consecutive early miscarriages or 1 late miscarriage were included during 5 to 8 weeks' gestation after a viable pregnancy was confirmed by ultrasonography.

Intervention: Women in the control group received multivitamin pills, and the intervention group received vitamins and 5000 IU of dalteparin-sodium for up to 24 weeks' gestation.

Measurements: Primary outcome was ongoing pregnancy at 24 weeks' gestation. Secondary outcomes included the live-birth rate and late pregnancy complications.

Results: At 24 weeks' gestation, 191 of 220 pregnancies (86.8%) and 188 of 214 pregnancies (87.9%) were intact in the intervention and control groups, respectively (absolute difference, -1.1 percentage points [95% CI, -7.4 to 5.3 percentage points]). The live-birth rates were 86.0% (185 of 215 women) and 86.7% (183 of 211 women) in the intervention and control groups, respectively (absolute difference, -0.7 percentage point [CI, -7.3 to 5.9 percentage points]). There were 3 intrauterine fetal deaths (1 woman had used LMWH); 9 cases of preeclampsia or the hemolysis, elevated liver enzyme level, and low platelet count (HELLP) syndrome (3 women had used LMWH); and 11 cases of intrauterine growth restriction or placental insufficiency (5 women had used LMWH).

Limitation: Placebo injections were not used, and neither trial staff nor patients were blinded.

Conclusion: Daily LMWH injections do not increase ongoing pregnancy or live-birth rates in women with unexplained RPL. Given the burden of the injections, they are not recommended for preventing miscarriage.

Primary funding source: Pfizer Pharma.

Publication types

  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Abortion, Habitual / prevention & control*
  • Anticoagulants / administration & dosage
  • Anticoagulants / therapeutic use*
  • Dalteparin / therapeutic use
  • Female
  • Heparin, Low-Molecular-Weight / administration & dosage
  • Heparin, Low-Molecular-Weight / therapeutic use*
  • Humans
  • Injections, Subcutaneous
  • Live Birth
  • Pregnancy
  • Vitamins / therapeutic use


  • Anticoagulants
  • Heparin, Low-Molecular-Weight
  • Vitamins
  • Dalteparin

Associated data

  • ClinicalTrials.gov/NCT00400387