Episode five flips a deeply intuitive instinct: pregnancy is not the time to back off immunosuppression, because the measured danger to the fetus is active maternal disease, not active maternal medicine. Once that principle is in place the medication rules become predictable, anything that maintained remission is continued and a small set of mechanism-toxic drugs is held. The molecular centerpiece is FcRn-mediated placental transfer, which loads IgG anti-TNF into cord blood by term but spares the Fab-fragment certolizumab, and that fact drives dose timing near term and infant vaccine decisions.

Topics covered

Active disease as the fetal danger
The central teaching against backing off
The safe-to-continue drugs
FcRn placental transfer and certolizumab
Dose timing near term
Infant live virus vaccination
The contraindicated drugs
Assessing disease activity in pregnancy

Key decisions

Biologic therapy is continued through delivery rather than held in the third trimester, because active disease at conception, not the medication, is what predicts adverse pregnancy outcomes.
Sulfasalazine requires folic acid supplementation bumped to two to three milligrams daily because the sulfa moiety antagonizes folate, and thiopurines are safe because the fetal liver cannot activate the prodrug.
Infliximab, adalimumab, and golimumab are IgG antibodies that cross via FcRn so cord levels can exceed maternal by term, while certolizumab is a Fab fragment with no Fc region and minimal transfer in any trimester.
For IgG anti-TNF agents the final dose is often spaced to roughly week thirty-two through thirty-eight so birth occurs at trough, and the biologic is resumed twenty-four hours after vaginal or forty-eight hours after cesarean delivery.
Live virus vaccination such as rotavirus was conservatively delayed six to twelve months in IgG-biologic-exposed infants, though the 2025 consensus now permits rotavirus for anti-TNF, IL-23 inhibitor, and vedolizumab exposure.
Methotrexate is absolutely contraindicated and stopped three to six months before conception, and tofacitinib, JAK inhibitors, ozanimod, thalidomide, and rifaximin are avoided.
CRP is unreliable in pregnancy because it rises physiologically, so fecal calprotectin is used for activity assessment and a C. difficile stool test is sent whenever a flare presentation comes through the door.

For the full chapter with MCQs, tables, and primary-guideline references, visit www.boardpearls.com.

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(00:00) - Active disease as the fetal danger
(00:27) - The central teaching against backing off
(01:58) - The safe-to-continue drugs
(02:59) - FcRn transfer and certolizumab
(04:00) - Dose timing near term
(04:48) - Infant live virus vaccination
(05:54) - The contraindicated drugs
(06:48) - Assessing disease activity in pregnancy