Sonography of fetal midgut herniation: normal size criteria and correlation with crown-rump length.

Forty-eight fetuses were prospectively evaluated to (1) determine the normal size range of herniated midgut and (2) correlate sonographically the timing of midgut herniation with CRL. All fetuses of CRL 38 mm or less, and two of six fetuses with a CRL of 40 to 42 mm, demonstrated midgut herniation. No fetuses with a CRL greater than 44 mm had this finding. The cord containing midgut increased roughly from 4 to 7 mm, in maximum dimensions, for CRL of 19 to 41 mm. An anterior abdominal wall mass greater than 7 mm at any CRL, or of any size in a fetus of CRL greater than 44 mm, is suggestive of a fetal anomaly. Alternatively, a cord base "mass" within the 4 to 7 mm range for a CRL of 19 to 44 mm can be considered normal and not to require any follow-up.