Fetal growth pathology score: a novel ultrasound parameter for individualized assessment of third trimester growth abnormalities

Abstract

Objectives: To study fetal growth in pregnancies at risk for growth restriction (GR) using, for the first time, the fetal growth pathology score (FGPS1).

Methods: A retrospective cohort study of GR was carried out in 184 selected SGA singletons using a novel, composite measure of growth abnormalities termed the FGPS1. Serial fetal biometry was used to establish second trimester Rossavik size models and determine FGPS1 values prior to delivery. FGPS1 data were compared to neonatal growth outcomes assessed using growth potential realization index (GPRI) values (average negative pathological GPRI (av - pGPRI)). Growth at the end of pregnancy was evaluated from differences in negative, individual composite prenatal growth assessment scores (-icPGAS) measured at the last two ultrasound scans. The FGPS1 and av - pGPRI values were used to classify fetal growth and neonatal growth outcomes, respectively, as Normal (N) or Abnormal (A).

Results: The risk of neonatal GR (based on birth weight (BW)) was moderate (MR: between 5th and10th percentiles (n = 113)) or significant (SR:<5th percentile) (n = 71)). Individual pregnancies were grouped into four categories, two representing agreement (N-N (29%), A-A (40%)) and two representing discordance (N-A (11%), A-N (20%)). In the largest and most variable subgroup (A-A,<5%tile, n = 49), there was a statistically significant correlation (0.63, p < .0001) between the FGPS1 and av - pGPRI. In N-A, all 20 cases (100%) had long last-scan-to-delivery intervals (1.9 weeks or greater), suggesting late development of the growth abnormality. For A-N, in approximately equal proportions, GR was improving, progressing or unclassifiable at the end of pregnancy.

Conclusions: Significant agreement between prenatal and postnatal growth assessments was found using a novel approach for quantifying fetal growth pathology (FGPS1). Discordances appear to be due to lack of appropriate prenatal scans or an inadequate set of neonatal measurements. Evidence for a quantitative relationship between assessment methods was seen in the largest and most variable subgroup. The FGPS1 has the potential for characterizing GR in the third trimester and may provide a means for predicting the severity of corresponding abnormal neonatal growth outcomes.

Keywords: Individualized growth assessment; SGA; longitudinal growth study.

Figure 1

Fetal size evaluation. Fetal growth evaluations first compared actual measurements to expected values (generated with Rossavik size models specified in the second trimester from growth velocity measurements). Percent deviations (%Dev) were then compared to their 95% reference range. If the %Dev was positive, the numerical part above the upper normal limit was designated the positive pathological %Dev (+%Dev_p) and indicated macrosomia. If the %Dev was negative, the numerical part below the lower normal limit was designated the negative pathological %Dev (−%Dev_p) and indicated growth restriction. For both +%Dev_p and −%Dev_p, all other %Dev values were considered to be zero.

Figure 2

Fetal growth pathology score (FGPS). This figure presents the data (left-hand table), mathematical definition (upper right-hand corner), and graph (lower right-hand corner) of the FGPS1 in a growth restricted fetus. All negative pathological percent deviations (−%Dev_p) for head circumference (HC), abdominal circumference (AC), femur diaphysis length (FDL) and estimated weight (EWT) collected up to each time point (shaded area) were averaged (FGPS_At) and plotted in the graph. Earlier onset, longer duration and greater magnitude (number and size of −%Dev_p) of the growth pathology increase the FGPS1. A: complete set of four anatomical parameters; t: sequential time points.

Figure 3

Neonatal size evaluation. Neonatal growth evaluations first compared actual birth measurements to expected values at their growth cessation ages (generated with Rossavik size models specified in the second trimester from growth velocity measurements). Growth potential index (GPRI) values were then compared to their 95% reference ranges. For GPRI’s above their reference ranges, the numerical part above the upper normal limit was designated the positive pathological GPRI (+pGPRI) and indicate macrosomia. For GPRI’s below their reference ranges, the numerical part below the lower normal limit was designated the negative pathological GPRI (−pGPRI) and indicate growth restriction. GPRI values within their reference ranges were assigned pGPRI values of zero. –pGPRI values were averaged to give av − GPRI values, neonates with values more negative than −0.69% being classified as growth restricted [9].

Figure 4

Types of prenatal growth assessment scores (PGAS). This figure illustrates how the negative anatomical parameter PGAS (−apPGAS) and negative individual composite PGAS (−icPGAS) values are calculated. They are the average of the negative pathological percent deviation (−%Dev_p) values for a given anatomical parameter during the third trimester (apPGAS) or the average of a set of −%Dev_p values obtained for specified group of anatomical parameters at a given time point in the third trimester (−icPGAS).

Figure 5

Fetal growth restriction patterns. a) Pre-delivery growth abnormality (Figure 5(a)): Growth abnormality only in last two weeks before delivery; confirmed by an abnormal av −pGPRI; b) Recovery from earlier growth abnormality (Figure 5(b)): less negative FGPS1 with advancing fetal age; confirmed by normal neonatal growth outcome; c) Progressive growth restriction (Figure 5(c)): increasingly negative FGPS1 throughout third trimester; no growth abnormalities found in GPRI’s for WT, HC or CHL. FGPS1: fetal growth pathology score; GPRI: growth potential realization index; av −pGPRI: average pathological growth potential realization index