Reference curves for the normal fetal small bowel and colon diameters; their usefulness in fetuses with suspected dilated bowel

Objectives: To establish reference curves of normal fetal small bowel and colon diameters and to assess the clinical applicability. Method: Serial longitudinal ultrasound examinations at 4-week intervals between 20 to 41 weeks of gestation in 39 low-risk fetuses. The largest loop of the small bowel and colon was identified. The bowel lumen short axis was measured. Linear mixed modeling was used to determine individual developmental trajectories. Twenty-eight fetuses with suspected bowel dilatation were analyzed relative to the reference curves. Results: Development of the small bowel and colon diameters was best described by a linear and cubic model, respectively. The intraobserver and interobserver concordance were >0.94. In cases with suspected bowel dilatation, normal fetal outcome occurred if the bowel dilatation was transient. Progressive increase of fetal bowel diameter was associated with pathology after birth. Cases with small bowel pathology had a z-score >8 after 25 weeks of gestation. Conclusion: We provided the first ultrasound reference curves for normal fetal small bowel and colon diameters. Progressive increase in the fetal bowel diameter z-score was highly predictive of intestinal abnormalities after birth. Longitudinal follow-up of dilated fetal bowel is important to distinguish normality from disease.