The Safety of Treating Women With Inflammatory Bowel Disease With Allopurinol and Low‐Dose Thiopurine During Pregnancy: A Single‐Center Experience

ABSTRACT Background Low‐dose thiopurine therapy in combination with allopurinol (LD‐THIO/ALLO) is a widely used treatment for inflammatory bowel disease (IBD). However, little is known about the effects of in utero exposure to this combination on pregnancy and birth outcomes. Methods In this retrospective, single‐center study, we included all patients with IBD treated with LD‐THIO/ALLO during conception and pregnancy between 2013 and 2023 at the Gastro Unit, Hvidovre Hospital, Copenhagen. Data were collected from electronic medical records and questionnaires. Results In total, 44 women with 62 pregnancies, including one twin pregnancy, and 59 live births were included. There was one spontaneous abortion and three induced abortions due to fetal genetic disorders, one because of trisomy 21 and two because of spinocerebellar ataxia. Obstetric complications occurred in eight pregnancies (13%), including preeclampsia, HELLP syndrome, hypertension, and/or gestational diabetes mellitus. Seven women (11%) had an IBD flare during pregnancy, none of which resulted in obstetric complications. Five children (9%) were born preterm, and four (7%) had low birth weight. No congenital malformations were reported. One child was born with facial nerve paralysis and was later diagnosed with hyper‐IgD syndrome. In total, 84% of the children were breastfed during maternal LD‐THIO/ALLO treatment. During the first year of life, one child had repeated infections and was transiently suspected of having an immune defect. Conclusions In this large, single‐center experience of LD‐THIO/ALLO treatment during pregnancy, no malformations or indications of increased risk of complications in pregnancy or birth were observed. Most children were breastfed, and no serious safety signals were reported in the first year of life. Treatment with LD‐THIO/ALLO appears to be safe during both pregnancy and breastfeeding.