Bowel circulation in normally grown and growth-restricted fetuses

The purpose of this study was to characterize bowel blood flow and its relationship with cerebral and placental circulations in normally grown and growth-restricted fetuses.

In a cross-sectional prospective study of singleton normally grown fetuses, Doppler blood flow pulsatility indices were measured in the superior mesenteric artery, middle cerebral artery, and umbilical artery from 19 to 38 weeks' gestation. The same Doppler parameters were examined in intrauterine growth-restricted (IUGR) fetuses and analyzed as two groups: (1) without a brain-sparing effect, defined as an umbilical artery/middle cerebral artery ratio of less than 1; and (2) with a brain-sparing effect, defined as an umbilical artery/middle cerebral artery ratio of greater than 1.

A total of 262 appropriate-for-gestational-age fetuses were analyzed for superior mesenteric artery Doppler pulsatility index values; 196 were simultaneously examined for umbilical artery and middle cerebral artery pulsatility index values. Forty-three IUGR fetuses were similarly analyzed. In appropriate-for-gestational-age fetuses, both the bowel and brain circulations showed a globally higher pulsatility index as pregnancy advanced, resulting in an almost constant middle cerebral artery/superior mesenteric artery ratio (r(2) = 0.079). The IUGR fetuses had a lower superior mesenteric artery pulsatility index compared to the appropriate-for-gestational-age fetuses, which was more pronounced in those with brain sparing (group 2) than in group 1 (Z = -0.97 and -0.53, respectively; P < .0001). The middle cerebral artery/superior mesenteric artery ratio was higher with respect to the appropriate-for-gestational-age fetuses in group 1, whereas the ratio in group 2 was lower (Z = 0.16 and -0.60).

We have shown the existence of a superior mesenteric artery sparing effect in IUGR fetuses. This reaction seems to correlate positively with the severity of the growth restriction.