Supplementary Material for: 15-Year Experience of Patch Testing During Pregnancy: Retrospective case-control study from a Tertiary Israeli Center

Background: Although patch testing (PT) is not contraindicated during pregnancy, most dermatologists defer testing due to lack of data and possibility that immunological changes might influence outcomes. In our center we routinely perform PT during pregnancy as it is not known to be teratogenic and may lead to significant improvements in quality of life. Objective: To assess whether pregnancy alters the outcome of PT. Methods: Retrospective, single-center case-control study was conducted at a tertiary Israeli dermatology clinic (2009-2023). Women who gave birth within 40 weeks of PT were identified, and for each, three age-, year-, and atopic dermatitis–matched controls were selected. Results: Of 3351 women tested, 54 (1.6%) were pregnant at the time of PT. Most were tested during the first trimester (63%). No significant differences were found in the frequency of positive patch test reactions between pregnant women and matched controls. The most common allergens in pregnant patients were nickel sulfate (61.1%), 2-hydroxyethyl methacrylate (13.64%), and fragrance mix II (5.5%). Limitations: Sample size was insufficient to detect differences in low-prevalence allergens. Potential referral and selection biases limit generalizability. Conclusion: Pregnancy does not appear to affect patch test outcomes in early and mid-gestation. Due to limited third-trimester representation, further studies are needed to determine whether reactivity remains consistent throughout all stages of pregnancy.