Is umbilical vein flow associated with abnormal fetal growth and adverse perinatal outcomes in low‐risk population?: multicenter prospective study

Abstract

ABSTRACTObjectivesTo investigate the relationship between the umbilical vein flow (UVF) measured close to term, and abnormal fetal growth and adverse perinatal outcome in a cohort of low‐risk pregnancies.MethodsThis was a prospective multicentre observational study conducted across two tertiary maternity units. Patients with a singleton appropriate for gestational age fetus between 35‐38 weeks of gestation were included. Pregnancy at higher risk of placental insufficiency or with fetal anomalies were excluded. At ultrasound examination, the abdominal circumference (AC), umbilical vein diameter and peak velocity of the umbilical vein were measured, and from these variables, the UVF/AC were calculated. The primary outcome was the occurrence of stunted fetal growth, defined as a drop of over 40 percentiles of the AC between 3rd trimester ultrasound and delivery. The secondary outcome was the occurrence of adverse perinatal outcome, defined as one of the following: neonatal acidosis (umbilical artery pH<7.15 and/or base excess>12) at birth and/or 5‐min Apgar score<7 and/or neonatal resuscitation and/or neonatal intensive care unit (NICU) admission.ResultsBetween April 2021 and March 2023, 365 women were included. The mean UVF/AC was 6.4 ± 2.6 ml/min/cm, and 31 (9.5%) cases were affected by stunted fetal growth. Stunted fetal growth was associated with a lower mean UVF/AC (5.4 ± 2.6 vs 6.5 ± 2.6 ml/min/cm; p=0.02) and a higher frequency of an UVF/AC < 10th percentile (8/35 or 22.9% vs 28/335 or 8.5%, p=0.01). Moreover, the UVF/AC showed an AUC of 0.65 (95% CI 0.55 – 0.75; p=0.004) in predicting the occurrence of stunted fetal growth and the optimal cut‐off value of the UVF/AC discriminating between normal and stunted fetal growth was 7.2 ml/min/cm. This value was associated with a sensitivity and a specificity of 0.77 (95% CI 0.60 – 0.90) and 0.33 (95% CI 0.28 – 0.39); a positive and negative predictive value of 0.11 (95% CI 0.07 – 0.15) and 0.93 (95% CI 0.87 – 0.97); respectively.Regarding the occurrence of adverse perinatal outcomes, this was independently associated with maternal age (aOR 0.93, 95% CI 0.87 – 0.99; p=0.04), UVF/AC Z‐score (aOR 0.53, 95% CI 0.3 – 0.87; p=0.01), and augmentation of labor (aOR 2.69, 95% CI 1.28 – 5.69; p=0.009). The UVF/AC showed an AUC of 0.65 (95% CI 0.56 – 0.73, p=0.005) and the optimal cut‐off value of the UVF/AC discriminating between normal and adverse perinatal outcome was 6.7 ml/min/cm. This value was associated with a sensitivity and a specificity of 0.70 (95% CI 0.54 – 0.83) and 0.40 (95% CI 0.34 – 0.45); a positive and negative predictive value of 0.14 (95% CI 0.09 – 0.19) and 0.91 (95% CI 0.85 – 0.95); respectively.ConclusionsOur data demonstrates an association between reduced UVF close to term, and stunted fetal growth and adverse perinatal outcomes in a cohort of low‐risk pregnant women, with a moderate ability to rule out, and a poor ability to rule in either outcome. Further studies are needed to establish whether the assessment of UVF can improve the identification of fetuses at risk of subclinical placental insufficiency and adverse perinatal outcome.This article is protected by copyright. All rights reserved.