Incidence of Anaphylaxis in Pregnancy
The incidence of anaphylaxis in pregnancy is rare, occurring in approximately 1.6 per 100,000 maternities (95% CI: 1.1-2.2), with severe perioperative obstetric anaphylaxis occurring at 1-3.5 per 100,000 deliveries. 1, 2
Epidemiological Data
The most robust population-based data comes from the UK Obstetric Surveillance System (UKOSS) study, which prospectively identified 37 confirmed cases of anaphylaxis over a 3-year period (2012-2015) among pregnant women in the UK 2. This translates to the incidence of 1.6 per 100,000 maternities, making it an uncommon but serious complication.
When specifically examining perioperative obstetric anaphylaxis (occurring during cesarean delivery or labor procedures), the RCOG Green-top Guideline reports an incidence range of 1-3.5 per 100,000 1. This slightly higher range reflects the increased exposure to potential allergens during surgical and anesthetic procedures.
Clinical Context and Triggers
The majority of anaphylaxis cases in pregnancy are drug-related, particularly:
- Antibiotics (most common): In the UKOSS study, 12 women developed anaphylaxis following prophylactic antibiotics at cesarean delivery 2
- Penicillins and cephalosporins: Four cases occurred in women with known penicillin allergies who received co-amoxiclav or cephalosporins 2
- Anesthetic agents: Common during perioperative period 1
- Other triggers include latex, animal allergens, and foods 1
Mortality and Morbidity
Despite the low incidence, anaphylaxis carries significant mortality risk with approximately 1% mortality rate 1. The UKOSS study documented:
- 2 maternal deaths (5% case fatality rate) 2
- 38% required intensive care admission 2
- 19% experienced additional severe maternal morbidities including cardiac arrests, hemorrhagic events, and thrombotic complications 2
Fetal/Neonatal Impact
Among infants whose mothers experienced anaphylaxis before delivery:
- 41% required neonatal intensive care admission 2
- Three preterm births occurred 2
- One infant required therapeutic cooling for neonatal encephalopathy 2
- No neonatal deaths were reported in this cohort 2
Important Clinical Caveats
Diagnostic challenges exist because normal physiological changes in pregnancy (hypotension, tachycardia) can mask or mimic anaphylaxis symptoms 1. Additionally, cutaneous manifestations may be less prominent in pregnant women, making recognition more difficult.
The data emphasizes that while anaphylaxis is rare, the consequences are severe when it occurs, particularly given the dual risk to both mother and fetus. The predominance of antibiotic-related cases highlights the importance of careful allergy history documentation before administering prophylactic antibiotics during delivery procedures.