Does Low Molecular Weight Heparin (LMWH) help in preventing preeclampsia?

LMWH is Not Recommended for Prevention of Preeclampsia

Low molecular weight heparin (LMWH) is not indicated to prevent preeclampsia, even in women with a history of prior early onset preeclampsia. 1

Evidence Against LMWH for Preeclampsia Prevention

• The International Society for the Study of Hypertension in Pregnancy (ISSHP) explicitly states that LMWH is not indicated to prevent preeclampsia, even in women with a history of prior early onset preeclampsia 1
• This recommendation is made with high confidence in the 2018 ISSHP guidelines, which represent the most authoritative guidance on management of hypertensive disorders in pregnancy 1

Recommended Preventive Strategies for Preeclampsia

First-Line Prevention

• Low-dose aspirin (75-162 mg/day) is recommended for women with strong clinical risk factors for preeclampsia, ideally started before 16 weeks but definitely before 20 weeks gestation 1
• Strong clinical risk factors include:
  • Prior preeclampsia
  • Chronic hypertension
  • Pregestational diabetes mellitus
  • BMI >30 kg/m²
  • Antiphospholipid syndrome
  • Receipt of assisted reproduction 1

Additional Preventive Measures

• Supplemental calcium (1.2-2.5 g/day) is recommended for women at increased risk of preeclampsia if their dietary intake is likely low (<600 mg/day) 1
• Regular exercise during pregnancy is recommended to maintain health and reduce the likelihood of hypertension 1

Recent Research on LMWH and Preeclampsia

Despite the guideline recommendations against LMWH for preeclampsia prevention, some recent research suggests potential benefits:

• A 2022 systematic review and meta-analysis found that LMWH was associated with a reduction in preeclampsia development (OR 0.62; 95% CI 0.43-0.90) in high-risk women 2
• A 2024 systematic review suggested that the combination of LMWH and low-dose aspirin was effective for preeclampsia prevention in high-risk women without thrombophilia 3
• A 2023 network meta-analysis ranked LMWH among the effective prophylactic strategies for preventing preeclampsia 4

However, these findings must be interpreted with caution as:

• The quality of evidence in these studies ranged from very low to moderate 2
• There was significant clinical and statistical heterogeneity across studies 2
• The guideline recommendations from major societies still do not support LMWH use for this indication 1

LMWH in Specific Clinical Scenarios

Thrombophilia and Pregnancy

• LMWH is indicated for prevention of venous thromboembolism (VTE) in specific high-risk scenarios, but not for preeclampsia prevention 1, 5
• For women with antiphospholipid antibody syndrome and a history of three or more pregnancy losses, prophylactic or intermediate-dose unfractionated heparin or prophylactic LMWH combined with low-dose aspirin is recommended 1
• For women with inherited thrombophilia and a history of pregnancy complications, antithrombotic prophylaxis is not recommended 1

Conclusion

Current guidelines from the International Society for the Study of Hypertension in Pregnancy clearly state that LMWH is not indicated for preeclampsia prevention, even in high-risk women with prior early onset preeclampsia. Low-dose aspirin remains the primary preventive strategy for women at high risk of preeclampsia, with calcium supplementation as an additional measure for those with likely low dietary calcium intake.