Umbilical Artery Doppler Velocimetry in a Sheep Model of Fetal Growth Restriction

Abstract

PurposeOvernourishing adolescent sheep dams results in placental and fetal growth restriction. We aimed to evaluate changes in the umbilical arterial (UA) Doppler waveform in relation to altered fetal growth velocity in these compromised pregnancies.Material & MethodsSingleton pregnancies of known gestational age were established in 36 adolescent ewe-lambs using embryo transfer. Dams were offered a control diet (n = 12) or overnourished (n = 24), resulting in normal and compromised fetal growth trajectories, respectively. Ultrasonographic fetal biometry and UA Doppler indices were measured weekly between mid-gestation and necropsy at 131.0 ± 0.30 days (term = 145days).ResultsAt 83.1±0.16days there were no significant differences in fetal biometry, but UA resistance index and systolic:diastolic ratio were already higher in overnourished ewes (p = 0.022). Differences in UA pulsatility index reached significance at 98.0 ± 0.07days (p ≤ 0.001). Values of all three Doppler indices progressively fell throughout gestation but remained different between groups (p = 0.001–0.032). Relative to controls, fetal abdominal circumference, renal volume and femur/tibia lengths were decreased from 104.6±0.13days (p = 0.001–0.023) in overnourished ewes whilst biparietal diameter was not reduced until 111.8±0.09days (p = 0.015), indicating an asymmetric pattern of growth. At necropsy fetal weight was lower in overnourished versus control groups (4110±168g vs. 5133±136g, p = 0.001). Relative brain weight was increased (11.1g/kg vs.9.1g/kg, p = 0.001) commensurate with fetal brain sparing.ConclusionChanges in UA Doppler indices precede slowing of the fetal growth trajectory in overnourished adolescent sheep dams. This may reflect altered vascularity in the downstream fetal placental compartment. PurposeOvernourishing adolescent sheep dams results in placental and fetal growth restriction. We aimed to evaluate changes in the umbilical arterial (UA) Doppler waveform in relation to altered fetal growth velocity in these compromised pregnancies. Overnourishing adolescent sheep dams results in placental and fetal growth restriction. We aimed to evaluate changes in the umbilical arterial (UA) Doppler waveform in relation to altered fetal growth velocity in these compromised pregnancies. Material & MethodsSingleton pregnancies of known gestational age were established in 36 adolescent ewe-lambs using embryo transfer. Dams were offered a control diet (n = 12) or overnourished (n = 24), resulting in normal and compromised fetal growth trajectories, respectively. Ultrasonographic fetal biometry and UA Doppler indices were measured weekly between mid-gestation and necropsy at 131.0 ± 0.30 days (term = 145days). Singleton pregnancies of known gestational age were established in 36 adolescent ewe-lambs using embryo transfer. Dams were offered a control diet (n = 12) or overnourished (n = 24), resulting in normal and compromised fetal growth trajectories, respectively. Ultrasonographic fetal biometry and UA Doppler indices were measured weekly between mid-gestation and necropsy at 131.0 ± 0.30 days (term = 145days). ResultsAt 83.1±0.16days there were no significant differences in fetal biometry, but UA resistance index and systolic:diastolic ratio were already higher in overnourished ewes (p = 0.022). Differences in UA pulsatility index reached significance at 98.0 ± 0.07days (p ≤ 0.001). Values of all three Doppler indices progressively fell throughout gestation but remained different between groups (p = 0.001–0.032). Relative to controls, fetal abdominal circumference, renal volume and femur/tibia lengths were decreased from 104.6±0.13days (p = 0.001–0.023) in overnourished ewes whilst biparietal diameter was not reduced until 111.8±0.09days (p = 0.015), indicating an asymmetric pattern of growth. At necropsy fetal weight was lower in overnourished versus control groups (4110±168g vs. 5133±136g, p = 0.001). Relative brain weight was increased (11.1g/kg vs.9.1g/kg, p = 0.001) commensurate with fetal brain sparing. At 83.1±0.16days there were no significant differences in fetal biometry, but UA resistance index and systolic:diastolic ratio were already higher in overnourished ewes (p = 0.022). Differences in UA pulsatility index reached significance at 98.0 ± 0.07days (p ≤ 0.001). Values of all three Doppler indices progressively fell throughout gestation but remained different between groups (p = 0.001–0.032). Relative to controls, fetal abdominal circumference, renal volume and femur/tibia lengths were decreased from 104.6±0.13days (p = 0.001–0.023) in overnourished ewes whilst biparietal diameter was not reduced until 111.8±0.09days (p = 0.015), indicating an asymmetric pattern of growth. At necropsy fetal weight was lower in overnourished versus control groups (4110±168g vs. 5133±136g, p = 0.001). Relative brain weight was increased (11.1g/kg vs.9.1g/kg, p = 0.001) commensurate with fetal brain sparing. ConclusionChanges in UA Doppler indices precede slowing of the fetal growth trajectory in overnourished adolescent sheep dams. This may reflect altered vascularity in the downstream fetal placental compartment. Changes in UA Doppler indices precede slowing of the fetal growth trajectory in overnourished adolescent sheep dams. This may reflect altered vascularity in the downstream fetal placental compartment.