Thiopurine metabolite shunting in late pregnancy increases the risk of intrahepatic cholestasis of pregnancy in women with inflammatory bowel disease, and can be managed with split-dosing.

BACKGROUND AND AIMS: The risk of intrahepatic cholestasis of pregnancy (ICP) is increased in thiopurine exposed pregnancies. Thiopurine 'shunting', with a 6-methylmecrcaptopurine (MMP) to 6-thioguanine (TGN) ratio of >11, progresses over pregnancy, and may promote ICP development. We aimed to explore the association between thiopurine exposure and ICP, including the hypothesized impact of thiopurine shunting, and identify risk minimization strategies.

METHODS: This prospective multi-centre cohort study compared thiopurine and biologic monotherapy exposed pregnant participants. Disease activity and obstetric outcome data, thiopurine metabolites, bile acids and transaminases were obtained preconception, in each trimester, at delivery, and post-partum. Thiopurine dose management was at the discretion of the treating physician.

RESULTS: 131 thiopurine and 147 biologic monotherapy exposed pregnancies were included. MMP/TGN ratio increased from preconception to third trimester (p<0.01), with approximately 25% of participants shunting in pregnancy. Second trimester split-dosing led to a decrease in the median MMP/TGN ratio from 18 (IQR 6-57) to 3 (IQR 2-3.5) at delivery (p=0.04). The risk of ICP was increased in thiopurine exposed pregnancies (6.7% (7/105) vs 0% (0/112), p<0.001), with all ICP cases occurring in the setting of antenatal thiopurine shunting. Thiopurine dose increases (RR 8.10 [95% CI 1.88-34.85] p=0.005) and shunting in third trimester (6.20 [1.21-30.73] p=0.028) and at delivery (14.18 [1.62-123.9] p=0.016) were associated with an increased risk of ICP.

CONCLUSIONS: Thiopurine exposure is associated with an increased risk of ICP, particularly following dose increases antenatally and with shunting in late pregnancy. The latter may be effectively managed with split dosing, although further studies are warranted.