The Effect of Changing Maternal Position from Left Lateral to Supine Position on Umbilical and Fetal Cerebral Blood Flow Indices

Abstract

Fetal brain sparing is a well-known phenomenon in obstetrics. It aims to maintain sufficient blood flow towards vital organ such as the brain, myocardium, and adrenals. This vascular adaptation takes place as a result of placental insufficiency that may occur in IUGR and preeclampsia. Maternal supine position in late gestation partially obstructs the aorta, due to the enlarged uterus, and leads to redistribution of blood flow, also impaired venous return due to compression of the inferior vena cava by the gravid uterus can also elicit supine hypotensive syndrome. This cross sectional study was carried out at Ain Shams university maternity hospital on fifty pregnant women with singleton pregnancy between 36 and 40 weeks of gestation who attended the ultrasound special care unit of the fetus between December 2014 and August2015 and were divided into two groups, Group A included 25 women with low risk pregnancy and Group B included 25 women with high risk pregnancy. In group A, our data demonstrated a statistically significant (p< 0.01)decrease in umbilical artery S/D((2.72±0.45 to 2.25±0.31)), PI(0.94±0.13 to 0.78±0.12) and RI(0.63±0.06 to 0.55±0.06) ratios after changing maternal posture from left lateral to supine position respectively.Similarily there was a statistically significant (p< 0.01) decrease in middle cerebral artery S/D(4.84±1.39 to 3.77±0.98), PI(1.52±0.26 to 1.36±0.27) and RI(0.78±0.05 to 0.72±0.06) ratios too by using paired t-test In group B, our data demonstrated a statistically significant (p< 0.01) decrease in umbilical artery S/D (2.52±0.33 to 2.23±0.25), PI(0.91±0.16 to 0.81±0.13) and RI (0.60±0.05 to0.55±0.05)ratios but not Vmean after changing maternal posture from left lateral to supine position as shown in .Similarily there was a statistically significant (p< 0.01) decrease in middle cerebral artery S/D(3.51±0.86to 3.04±0.68), PI(1.30±0.30 to 1.15±0.27)and RI(0.70±0.07 to 0.66±0.07) ratios but not Vmeanby using paired t-test This observation may be explained by aortocaval compression by the gravid uterus in supine position leads to decrease in placental blood flow and acute hypoxia which elicit a brain sparing effect leading to decrease vascular resistance in the cerebral and umbilical arteries to maintain sufficient blood supply to the brain to compensate for acute hypoxia resulted from pressure of the gravid uterus on the IVC and the aorta.