Fetal weight projection model to define growth velocity and validation against pregnancy outcome in a cohort of serially scanned pregnancies

Abstract

What are the novel findings of this work?We have defined limits for normal, slow and accelerated fetal growth which are specific to the ultrasound measurement interval, have a false-positive rate limited to 10% and are associated with perinatal outcome. Two-thirds of pregnancies at increased risk of stillbirth due to slow growth were not small-for-gestational age at the last scan. What are the clinical implications of this work?This method for defining normal and abnormal fetal growth presents an additional, size-independent parameter for antenatal surveillance by serial fetal biometry. Greater emphasis on monitoring growth velocity will help identify pregnancies at risk and prevent adverse perinatal outcome.

Outcome‐based comparative analysis of five fetal growth velocity models to define slow growth

“…The POWR method was the only one able to identify non-SGA fetuses that had a significantly increased risk of stillbirth in this cohort (Table 2). With this standard, 16 671 (10.1%) fetuses had slow growth between the last two scans, and 11 237 (67.4%) of these were not SGA according to the last EFW; similar to our previous finding (66.2%) with this method 11 . The 25 stillbirths in this group of non-SGA EFWs had a median fetal-weight centile of 52.6 at the last scan.…”

“…We examined the characteristics of the stillbirths in the POWR-only groups in Table 3 that were missed by the other models. The 11 cases that were not defined as having slow growth according to FVL 20 were POWR-positive because the second EFW, about 28 days later, was on average 9.9% below the projected weight, thus exceeding the −8.2% cut-off defining slow growth at this scan interval 11 . The average weight difference between scans was 655 g, which gave an average velocity of 23.6 g/day, well above the < 20 g/day definition of slow growth according to the linear model.…”

“…Several methods have come into clinical use to define lower limits for serially estimated fetal weight (EFW), including: (1) a trajectory below a fixed minimal growth rate of 20 g per day throughout the third trimester 14 , recommended currently by the National Health Service (NHS) in England 15 ; (2) a > two‐quartile (50‐centile) drop over an unspecified measurement interval, according to a Delphi consensus statement 16 adopted by the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) 17 and the International Federation of Gynecology and Obstetrics (FIGO) 18 guidelines; (3) a > 30‐centile drop, based on studies with 8‐week 19 or 16‐week 20 measurement intervals; (4) a fetal growth trajectory slower than the third‐centile line on a customized chart 21 ; and (5) a variable cut‐off model to project measurement‐interval‐specific normal ranges for fetal weight 11 , calculated within GROW software 22 or by a standalone tool 23 .…”

Fetal Growth Velocity according to the Mode of Assisted Conception

“…Our results suggest that compared to spontaneous conception, ART pregnancies those after oocyte donation, being at the highest risk of defective growth velocity, are warranted a closer follow-up by serial ultrasound and growth velocity assessment. A recent population-based series including more than 100,000 high-risk pregnancies showed that slow growth velocity is independently associated with perinatal mortality, even in the range of birthweights above the 10th centile [36].…”

“…A decreased growth velocity is considered a parameter of placental dysfunction and fetal growth restriction [30,31]. Indeed, recent evidence shows a significant correlation with indicators of placental dysfunction, even in those fetuses considered adequate for gestational age (GA) [32][33][34][35], including an independent association with perinatal mortality [36]. Moreover, its use during the second half of pregnancy improves the characterization of fetuses at higher risk [37][38][39][40][41][42].…”