Am J Perinatol 1997; 14(3): 119-124
DOI: 10.1055/s-2007-994110

© 1997 by Thieme Medical Publishers, Inc.

Pregnancy Outcome Following First Trimester Exposure to Antihistamines: Meta-Analysis

Arnold Seto, Tom Einarson, Gideon Koren
  • Motherisk Program, Division of Clinical Pharmacology and Toxicology, Department of Pediatrics and Research Institute, The Hospital for Sick Children, Toronto, Faculties of Medicine and Pharmacy, University of Toronto
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Publication History

Publication Date:
04 March 2008 (online)


To determine the relative risk for major malformations associated with antihistamine (H1 blockers) exposure in the first trimester of pregnancy, a literature search of all studies examining the association between antihistamines and major malformations for the period 1960 to 1991 was conducted, followed by meta-analysis. Odds ratio was calculated using the Mantel-Haenszel method. Twenty-four controlled studies met the inclusion criteria with more than 200,000 participating women. The summary odds ratio of major malformations associated with antihistamines taken during the first trimester was 0.76 (95% Cl: 0.60-0.94). This analysis indicates that H1 blockers used mainly for morning sickness during the first trimester do not increase the teratogenic risk in humans and may, in fact, be associated with a protective effect. More study is needed to verify the possibility that by preventing vomiting, antihistamines may ensure better metabolic conditions to the fetus and thus may reduce some birth defects. Alternatively, it is possible that pregnancies characterized by vomiting are associated with better outcome due to other reasons, such as hormonal status or placental function. Women suffering from morning sickness which is not controlled by nonpharmacological methods can safely use antihistamines.