Lovenox Side Effects in Pregnancy

Lovenox (enoxaparin) is a blood thinner, often referred to as a low molecular weight heparin (LMWH), that’s given by daily injection. LMWH's offer a more stable and predictable course of action in the body and therefore minimize the bleeding risks seen with unfractionated heparin. According to the American College of Obstetricians and Gynecologists, Lovenox is a safe and effective treatment for both the prevention and treatment of venous thromboembolism (blood clots) in pregnancy.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.

Common Side Effects

The majority of Lovenox side effects occur with the same frequency in both pregnant and non-pregnant individuals. Lovenox is injected subcutaneously (under the skin) into the abdomen once or twice daily and can be associated with localized pain and bruising at injection sites. Fever, nausea and diarrhea have also been reported. Elevations in liver enzymes up to three times the normal value have been seen in as many as 6 percent of patients. These levels generally normalize with drug termination.


The risk of postpartum hemorrhage is a major concern for all pregnancies. A retrospective study of 2,777 pregnancies with LMWH use revealed less than 2 percent of patients using Lovenox experienced a major hemorrhage, which was not significantly different from those patients not using LMWH. The majority of cases with major hemorrhage were directly related to expected obstetric causes, however, and not directly related--though possibly enhanced--by the effects of Lovenox.

Low Platelet Count

Thrombocytopenia (lower than normal number of platelets in the blood) has been implicated with standard, unfractionated heparin use and has been referred to as heparin-induced thrombocytopenia (HIT). This condition has been seen so infrequently with LMWH that the American College of Chest Physicians does not recommend routinely monitoring platelet counts in pregnant patients treated with Lovenox.

Bone Density Loss

Loss of bone density, osteoporosis and associated fractures have long been established risks of standard heparin therapy, and it was assumed those risks applied to LMWH as well. However, according to “Human Reproduction,” bone loss observed in pregnancy was not statistically different between patients who used LWMH and those who did not. Another retrospective study of nearly 1,200 pregnant women taking Lovenox also revealed no cases of osteoporosis or osteoporotic fractures. Although bone loss is commonly cited as a potential side effect of Lovenox, these studies would suggest otherwise.

Epidural/Spinal Hematoma

There have been rare reports of serious neurologic injury, including paralysis, from uncontrolled bleeding in patients taking Lovenox who underwent epidural catheter placement and spinal anesthesia. Both the American College of Obstetricians and Gynecologists and the American Society of Regional Anesthesia advise delaying epidural anesthesia use for 12 to 24 hours after the last dose of administered Lovenox in order to minimize the risk of significant bleeding. After the implementation of these guidelines, there were no complications observed in follow-up studies. The use and timing of epidural anesthesia in labor and delivery for patients taking Lovenox nonetheless remains a controversial issue.