Trimester by trimester, when should scanning be performed, what constitutes a minimal exam in terms of segments, bowel wall thickness, and Doppler threshold, what are the fallback options when IBUS expertise is unavailable, and how should limited terminal ileum views in the second trimester be managed?
How should elevated FCP be weighed when IUS is normal? And what re-scan interval do you recommend after escalation?
Dr. Prentice: When discordant, we focus predominantly on targeting FCP < 100 and, ideally, sonographic remission. We rely very little on symptoms in pregnancy, as they are highly unreliable and can be masked by pregnancy-induced constipation, nausea, and fatigue. If IUS is normal and FCP is elevated, I would suspect rectal disease; if there is no history of rectal disease, I would obtain an MRE in CD. I often do a trial of topical therapy when FCP is elevated with a normal IUS; if there is no response, I become more suspicious that disease not visible on IUS is present—either due to limited views or proximal small-bowel involvement—and I additionally consider a flexible sigmoidoscopy. I re-scan 4 weeks after escalation.
What mechanisms might link IUS-detected transmural inflammation to adverse obstetric outcomes, and what study designs would best test causality?
Dr. Prentice: I doubt there is an all-encompassing answer to that question. Active disease in early pregnancy likely impacts the placentation process, while active disease in later pregnancy may affect placental function. The impact of active disease more broadly on energy expenditure, and its contribution to poor gestational weight gain, requires further investigation. The ethics of not acting on active disease in the context of pregnancy—given the known associations with adverse obstetric outcomes—will limit the ability to conduct any randomized studies. Including sonographic and serum assessments of placental function would be useful.
How did you derive BWT udner 6 mm (CD) and IUS remission (UC) as pragmatic pregnancy targets, and how should BWT over 6 mm without hyperemia (possible fibrosis) factor into escalation decisions?
Dr. Prentice: A BWT > 6 mm in the setting of CD should be acted upon, even in the absence of hyperemia, whereas a BWT of 3–4 mm is more likely representative of fibrosis. I wouldn’t be comfortable attributing a BWT of 6 mm to fibrosis alone in any context; however, in the very rare circumstance that it represents a fibrotic stricture, I would review the submucosa-to-mucosa thickness ratio and any previous scans, if available. Again, we know from the STRIDENT study that most “fibrotic” strictures still have an inflammatory component, so I would act; the harms of missing—and failing to act upon—active disease in pregnancy outweigh the risks of the majority of medical therapies available to us. We pragmatically picked < 6 mm for CD given the low rates of achieving complete sonographic remission in CD in existing biologic induction trials (approximately 25% across the board for anti-TNF, ustekinumab, and vedolizumab), whereas for UC, some associations with adverse outcomes were observed with any active disease. A larger study enabling more robust subgroup analyses would help refine these targets.
Dr. Prentice is with the Department of Gastroenterology, Monash Health, Victoria, Australia.
