1.INTRODUCTION
FGR accounts for approximately 5%–10% of singleton pregnancies1. This growth disorder is associated with an increased risk of APO and long-term impacts2 3. At present, prenatal recognition of small size by ultrasound, which minimizes rates of APO to some extent, is the most commonly method for identifying intrauterine growth disorders. However, it still fails to detect more than 25% of late-onset FGR 4-6. One possible reason for failure to identify late-onset FGR is that the ultrasound examination was done in the early third-trimester pregnancy6 7.
The feto-placental circulation is crucial for fetal development and growth. At present, the umbilical artery (UA) Doppler studies, including the umbilical pulsatility index (UA-PI) and the ratio of the systolic peak value and the end-diastolic velocity of the umbilical artery (UA-S/D), is the primary method for evaluating feto-placental circulation. However, as reported by some published studies, placental insufficiency in late-onset FGR often goes undetected by UA Doppler scan8 9, which brings a problem in assessing APO of those SGA infants. It is now widely acknowledged that large numbers of near-term SGA infants with normal UA Doppler studies are identified as late-onset FGR, which are at risk of APO10-12.
It is widely known that the placental volume blood flow is reduced in FGR. The decrease of placental volume blood flow might even occur before the increase of UA-PI in the fetuses with growth restriction13. One longitudinal study reported that the UA velocities can reflect placental blood flow and thus the feto-placental circulation 14. However, to the best of our knowledge, whether the UA velocities are decreased in FGR has not been determined.
Therefore, the main purpose of this study was to investigate the discordances of UA velocities in the FGR, SGA and AGA with normal UA Doppler at 37 weeks’ gestation, and to investigate the value of UA velocities for predicting FGR. We hypothesized that the UA absolute velocities might be decreased with the severity of growth restriction, even in those with normal UA Doppler, which can contribute to an early prediction of FGR with normal UA Doppler.