You are right to plan a serum bile acid test at 31 weeks since itching in pregnancy may indicate intrahepatic cholestasis of pregnancy (ICP), which needs close monitoring.
• Bile acid test: Usually best done fasting (8–12 hours), because food intake can affect the levels and may give falsely lower values.
• Glucose test: Already requires fasting if you are doing a
fasting blood sugar or OGTT (oral glucose tolerance test).
• ✅ So yes, you can combine both tests in the same fasting sample.
Next Steps
Connect if bile acids are high. Treatment and closer fetal monitoring are needed.