Effects of chronic reduction in uterine blood flow on fetal and placental growth in the sheep

Pregnancy is associated with a significant increase in uteroplacental blood flow (UBF), which is responsible for delivering adequate nutrients and oxy gen for fetal and placental growth. The present study was designed to deter mine the effects of vascular insufficiency on fetal and placental growth. T hirty-nine late-term pregnant ewes were instrumented to investigate the eff ects of chronic UBF reduction. Animals were split into three groups based o n uterine blood flow, and all animals were killed on gestational day 138. U BF, which began at 851 +/- 74 ml/min (n = 39), increased in controls (C) to 1,409 +/- 98 ml/min (day 138 of gestation) and in the moderately restricte d (RM) group to 986 +/- 69 ml/min. In the severely restricted (RS) group, U BF was only 779 +/- 79 ml/min on gestational day 138. This reduction in UBF significantly affected fetal body weight with RM fetuses weighing 3,685 +/ - 178 g and R-S fetuses weighing 2,920 +/- 164 g compared with C fetal weig hts of 4,318 +/- 208 g. Fetal brain weight was not affected, whereas ponder al index was significantly reduced in RM (2.94 +/- 0.09) and RS fetuses (2. 49 +/- 0.08) compared with the value of the C fetuses (3.31 +/- 0.08). Plac ental weight was also significantly reduced in the RM group, being 302 +/- 24 g, whereas the RS group placenta weighed 274 +/- 61 g compared with the C values of 414 +/- 57 g. Fetal heart, liver, lung, and thymus were all sig nificantly smaller in the RS group. Thus the present study shows a clear re lationship between the level of UBF and both fetal and placental size. Furt hermore, the observation that fetal brain weight was not affected, whereas fetal body weight was significantly reduced suggests that this experimental preparation may provide a useful model in which to study asymmetric fetal growth restriction.