SummaryBackground and AimsInflammatory bowel disease (IBD) activity during pregnancy is associated with adverse pregnancy outcomes. We aimed to identify key clinical characteristics that predict disease activity during pregnancy.MethodsBetween January 2008 through 2021, we identified all singleton pregnancies among women with IBD recorded in patient and birth registries at a tertiary IBD centre in Denmark. Maternal and infant data were retrieved from medical records. Demographics, Physicians Global Assessment (PGA) of disease activity 6 months prior to pregnancy and in all three trimesters of pregnancy and pregnancy outcomes were recorded.ResultsIn 609 pregnancies, we observed 603 (99.0%) live births. Disease activity in one or more trimesters was seen in 283 women (46.5%). UC phenotype was associated with an increase in risk of disease activity (adjusted OR = 2.6 [1.8–3.9]; p < 0.001). Disease activity within 6 months prior to conceiving (169 women [27.7%]) was associated with an increased risk of continuous disease activity during pregnancy (adjusted OR of 5.3 [3.5–8.2]; p < 0.001). Disease activity during a previous pregnancy was associated with an increased risk of flares in subsequent pregnancies (adjusted OR of 3.2 [1.5–6.6]; p = 0.002). Sustained clinical remission throughout pregnancy was associated with an increased probability of normal birth term, birthweight and low risk of fetal growth restriction (FGR) and stillbirth.ConclusionPredictors for disease activity include disease activity in a previous pregnancy and/or prior to conception, as well as UC phenotype. Reassuringly, women with IBD in remission are not at increased risk of adverse pregnancy outcomes.