Factors affecting umbilical venous perfusion during experimental cord knotting.

The aim was to determine experimentally the factors that increase the risk of venous occlusion by applying a standardised tightening force to isolated perfused umbilical cords tied in a true knot in vitro. Umbilical cords were collected from patients undergoing Caesarean section. Cords were clamped, isolated and studied within 15 min. The umbilical vein was cannulated, the cord tied in a true knot and traction was applied using standard weights. The umbilical vein was perfused with modified Krebs solution at a constant pressure of 40 mmHg and the attached weight increased until perfusion ceased. The cord mass index (weight/length), hydration index/100-[(dry weight/wet weight)x100], and coiling index (coils/length) were determined. Cord morphometric analysis was performed on 193 cords. Intra uterine growth restriction was associated with decreased cord mass index (p=0.002) and increased coiling index (p=0.002). Venous perfusion experiments were performed on 75 cords. Using multivariate regression analysis, cord morphometric factors that increased the risk of cord occlusion were decreased cord mass index (p=0.008), decreased cord hydration index (p=0.004), and low venous flow capacity (p=0.001). During experimental cord knotting with applied traction, the susceptibility to venous occlusion was increased with low cord mass index, low cord hydration index and low venous flow capacity. These cord characteristics were associated with low fetal body weight and intrauterine growth restriction. An increased susceptibility to cord occlusion may contribute to the higher perinatal morbidity and mortality in growth restricted pregnancies.