(579) Does umbilical venous diameter or time-averaged maximum velocity correlate better with fetal outcome in growth-restriction?

Reduced umbilical vein flow (UVF) is a characteristic of fetal growth restriction (FGR) and is associated with adverse neonatal outcomes. UV diameter (UVD) and time-averaged maximum velocity (TAMAX) determine UVF, but which variable is most important and whether they correlate with outcomes is unknown. Our objective was to determine which variable correlated best with 1) standard Doppler methods and 2) immediate neonatal outcomes.  

Study Design:

Singleton pregnancies with FGR defined as having estimated fetal weights (EFW) < 10^th centile were studied between 20–39 weeks gestational age (GA). Serial measurements of UVD and TAMAX were taken according to methods previously reported. Middle cerebral artery (MCA) and umbilical artery (UA) pulsatility indices (PI) were collected by routine methods.

Because UVD and TAMAX values pursued widely varying trajectories (Figure 1), mean UVD and TAMAX were used as risk factors for neonatal outcomes and the last UA and MCA PI measurements were taken before delivery.

Linear and logistic regression models were used to assess associations of mean UVD and TAMAX with outcomes. Mean UVD and TAMAX were later standardized and modeled in multivariable models to compare relative associations.

Results:

Higher mean UVD was associated with increased GA at delivery, birth weight and length, and decreased odds of neonatal intensive care unit (NICU) admission and cesarean delivery, as well as lower UA PIs. Similar relations were found with mean TAMAX and outcomes, although stronger associations were found for MCA PI (Table 1a).

When UVD and TAMAX were standardized in multivariable models, mean UVD had a stronger association than mean TAMAX for most outcome variables (Table 1b).

Conclusion:

UVD had a stronger association with neonatal outcomes than TAMAX. Although the TAMAX represents the driving force of flow out of the placenta, the UVD itself, as a rate-limiting factor, may be a driver of outcomes in FGR and should be evaluated for a management role in future studies. Whether MCA PI is a better predictor than UVF variables needs further investigation.