The role of antifactor Xa monitoring in the dosing and administration of low-molecular-weight heparins in pregnancy: a systematic review and meta-analysis.

In 30 seconds

This systematic review and meta-analysis assessed thromboembolic complications and major bleeding with fixed, weight-based, and anti-Xa-monitored low-molecular-weight heparin dosing during pregnancy, including use for thromboprophylaxis, VTE treatment, and mechanical heart valves. It included 94 studies: 53 case series, 30 cohort studies, and 11 randomized trials. For thromboprophylaxis and VTE treatment, pooled event rates and 95% CIs overlapped across dosing approaches. In pregnancies with mechanical heart valves, pooled rates were 2.7% for maternal death, 7.9% for thromboembolic complications, and 8.4% for major bleeding. Evidence certainty was low to very low.

Key findings

• For thromboprophylaxis and VTE treatment, pooled thromboembolic and major-bleeding event rates and 95% CIs overlapped across fixed, weight-based, and anti-Xa-monitored dosing.
• With mechanical heart valves, pooled rates were 2.7% (95% CI, 0.3%-6.5%) for maternal death, 7.9% (95% CI, 2.8%-14.6%) for thromboembolic complications, and 8.4% (95% CI, 2.0%-17.2%) for major bleeding.
• Across anti-Xa-monitored regimens for mechanical heart valves, pooled single-arm event rates and 95% CIs overlapped; certainty of evidence was low to very low.

Why it matters

Pregnancy anticoagulation requires balancing prevention of thromboembolism against bleeding, including in people with mechanical heart valves. This synthesis describes outcomes reported with commonly used LMWH dosing approaches, but overlapping estimates do not establish that the approaches are equally effective or safe. The low certainty and imprecision are important when interpreting apparent similarities.

What to keep in mind

The authors note small sample sizes, wide 95% CIs, and low certainty of evidence, largely due to imprecision, risk of bias, and publication bias.