Does umbilical cord milking at birth increase superior vena cava blood flow?

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Umbilical cord milking (UCM) in preterm infants does not improve functional cardiac outcomes, neonatal morbidity or mortality, according to a Canadian randomized clinical trial. The study, published in 2019 in BMJ Journal – ADC Fetal & Neonatal edition, was conducted at a single tertiary care center: IWK Health Centre in Halifax, Nova Scotia, with roughly 5,000 births yearly.

UCM was compared to immediate cord clamping (ICC) in 73 infants. The infants were born to eligible women who presented in preterm labor between 24 and 31 weeks’ gestation. Randomization was to either UCM three times before cord clamping or ICC. The primary outcome was systemic blood flow as represented by echo-derived superior vena cava (SVC) flow at 4 to 6 hours after birth. Secondary outcomes included cardiac output, neonatal morbidities and mortality during NICU stay. Of the 73 infants, 37 were randomized to UCM and 36 to ICC.

Hemoglobin on admission was significantly higher in the UCM group than in the ICC group: 16.1 g/L vs. 15.0 g/L (P = 0.049), a mean difference of 1.1 (95% CI: 0.003 to 2.2). As in other studies, this finding “suggests an achieved successful placental transfusion and contradicts the assumption that the lack of increase of systemic blood flow could be attributed to inconsistent procedure or insufficient placental transfusion,” wrote the investigators.

But there were no statistically significant differences detected between the two groups in mean SVC flow at a mean age of 5 hours: 88.9 ±37.8  mL/kg/min for UCM and 107.3 ±60.1 mL/kg/min for ICC (P = 0.13), for a mean difference of -18.4 (95% CI: −41.7 to 5.0 mL/kg/min). Similarly, there was no significant difference at 11 hours of age for mean SVC flow: 102.5 ±41.8  mL/kg/min and 90.6 ±28.4 mL/kg/min, respectively (P = 0.17), for a mean difference of 12.0 (95% CI: −4.7 to 28.7 mL/kg/min).

Two study limitations are that the sample size was calculated for systemic blood flow, thus underpowered to evaluate clinical outcomes, and that it was not possible to ensure that the UMC was performed as outlined in the protocol.

“More research is needed before routine cord milking can be recommended for very preterm infants,” the investigators wrote.