Performance of computerized cardiotocography-based short-term variation in late-onset small-for-gestational-age fetuses and reference ranges for the late third trimester.

PURPOSE: Fetal Doppler changes are well characterized in early-onset small-for-gestational-age (SGA) and fetal growth restriction (FGR) but less well characterized where the condition is late-onset. The aim of the study was to evaluate the role of computerized CTG (cCTG)-based short-term variation (STV) in late-onset SGA and FGR as an additional monitoring modality and to establish STV reference ranges in late third trimester healthy pregnancies.

METHODS: Of 86 late-onset SGA fetuses diagnosed after 32 weeks, 66 were diagnosed with FGR. 138 healthy pregnancies acted as controls. All underwent umbilical artery pulsatility index (PI), middle cerebral artery PI, cerebroplacental ratio and mean uterine artery PI. cCTG recordings were analyzed by Sonicaid FetalCare software for STV calculation as described by Dawes/Redman.

RESULTS: Median interval between inclusion and delivery was 13 (interquantile range = 4-30) days in the FGR group, 22 (12-37) days in the SGA group and 25 (10-40) days in the control group. STV was not different between controls (11.2 ms, 9.7-13.1), late-onset SGA (11.2 ms, 8.1-12.6) and FGR (10.5 ms, 8.5-12.4) fetuses. A greater proportion of late-onset SGA fetuses had STV < 5th percentile (7/86) compared to controls (4/138) (8.1% vs. 2.9%, p = 0.077). In the control group a significant positive correlation was seen between STV, and 1-min (ρ = 0.195, p = 0.026), 5-min (ρ = 0.247, p = 0.004) and 10-min (ρ = 0.211, p = 0.014) Apgar values.

CONCLUSIONS: We report no significant difference in STV median values between controls, SGA and FGR pregnancies. However, more SGA fetuses had a low STV compared to controls. Prospective longitudinal studies are needed to investigate if low STV is a useful surveillance method for late-onset FGR.