Sept 20, 2021: Should Antivenom be Administered to Pregnant Women?

A 25-year-old female presents to the Emergency Department for evaluation of a snake bite. She is 21weeks pregnant. She states that approximately 1 hours prior to arrival she was bite by a timber rattle snake, Crotalus horridus, on the dorsum of her right foot. On arrival the patient has significant swelling and ecchymosis of the foot along with two puncture wounds. The patient is hemodynamically stable and fetal heart tones show no signs of fetal distress. Laboratory evaluation showed thrombocytopenia, and prolongation of the INR and aPTT. Over the next 1 hour the patient has significant progression of the swelling and ecchymosis up her right lower extremity to her mid-calf. What is the best course of action? 

Snakebites in pregnancy are uncommon, accounting for <1% of the ~5,ooo cases of venomous snakebites in the US each year.1 Though this is a rare occurrence it can result in significant maternal and fetal morbidity and mortality, with maternal death and or fetal loss occurring in up to 10 and 43% of the reported cases, respectively.2 Adverse obstetric outcomes including miscarriage, preterm birth, placental abruption, and stillbirth have all been associated with envenomation in pregnancy.3,4 Adverse pregnancy effects may be due to the direct effects of venom on the mother or fetus or secondary to primary maternal illness. So, what should clinicians do when they encounter this rare but serious medical situation? Perhaps the most anxiety provoking aspect of treatment is the use of antivenom therapy for those with moderate to severe toxicity. There have been no studies evaluating the risk of antivenoms during pregnancy, nor have there been reports of adverse effects of antivenom administration in pregnancy.5  Reproduction studies regarding the Crotalinae antivenom, CroFab ® (BTG), have not been reported in animals or humans. A systematic review of antidote use during pregnancy was published in 2003. Few cases of antivenom were included, though the authors concluded that no antivenom was clearly associated with negative fetal effects and recommended treatment to improve maternal morbidity and mortality.5 It is unlikely that CroFab ® (BTG) crosses the placenta in large amounts.6  With the current limited body of knowledge regarding envenomation in pregnancy, we are essentially left with the old obstetric dogma: what is good for the mother is good for the fetus. Despite these limitations, the limited available evidence suggests that optimal management includes a venom-specific approach, including supportive care, antivenom administration in appropriate cases, treatment of anaphylaxis if present, and fetal assessment.4


This question of the week was prepared by Blake Gruenberg, MD

Pediatric Emergency Medicine Fellow



1.         Seifert SA, Boyer L V, Benson BE, Rogers JJ. AAPCC database characterization of native U.S. venomous snake exposures. Nativ US snake Expo. 2009;47(4):327-335. doi:10.1080/15563650902870277

2.         Langley RL. A review of venomous animal bites and stings in pregnant patients. Wilderness Environ Med. 2004;15(3):207-215. doi:10.1580/1080-6032(2004)15[207:AROVAB]2.0.CO;2

3.         Pantanowitz L, Guidozzi F. Management of snake and spider bite in pregnancy. Obstet Gynecol Surv. 1996;51(10). doi:10.1097/00006254-199610000-00021

4.         Brown SA, Seifert SA, Rayburn WF. Management of envenomations during pregnancy. Clin Toxicol. 2013;51(1):3-15. doi:10.3109/15563650.2012.760127

5.         Bailey B. Are There Teratogenic Risks Associated with Antidotes Used in the Acute Management of Poisoned Pregnant Women? Birth Defects Res Part A - Clin Mol Teratol. 2003;67(2). doi:10.1002/bdra.10007

6.         Forestier F, Daffos F, Capella-Pavlovsky M. Low molecular weight heparin (PK 10169) does not cross the placenta during the second trimester of pregnancy study by direct fetal blood sampling under ultrasound. Thromb Res. 1984;34(6). doi:10.1016/0049-3848(84)90260-3

Fortunately, this scenario doesn’t occur very often.  IF there was ever a time to call the Poison Center, it would be when you have a pregnant patient with a snake envenomation.


I am interested in any questions you would like answered in the Question of the Week. Please email me with any suggestion at


Donna Seger, MD

Executive Director

Tennessee Poison Center

Poison Help Hotline: 1-800-222-1222