STV Analysis Versus Visual Evaluation of Cardiotocography in FGR

Severe, early-onset fetal growth restriction (FGR, <32 weeks gestation) is a condition in which the fetus does not reach its growth potential due to placental insufficiency[. This condition affects about 0.3% of pregnancies, accounting for an estimated 15,000 babies in Europe being born premature below 32 weeks gestation. The main clinical dilemma of FGR lies in the timing of birth, given the balance of risks of antenatal mortality and severe damage to organs and the aggravated neonatal effects of prematurity: death or survival with severe neurodevelopmental impairment. The mainstay of clinical management in these cases pivots around the anticipation of the risk of fetal demise from placental oxygenation failure. The monitoring variables that are currently available comprise assessment of the severity of metabolic insufficiency (fetal size and growth, Doppler ultrasound, serum biomarkers) and the early detection of progressive fetal hypoxia with cardiotocography (CTG). The common approach is to deliver the fetus when signs of advanced hypoxia appear on CTG. A delicate balance exists between having the fetus born (too) early and facing the risks of extreme prematurity combined with a very low birthweight; and between delivering the fetus (too) late when the fetus has the disadvantage of hypoxia at birth. The decision when to deliver the fetus, is made mostly based on the CTG. The inter- and intra-observer variability could be overcome by software analysis according to the original Dawes&Redman algorithm. The software calculates the short-term variation (STV) of the inter-beat interval expressed in milliseconds, and a range of secondary calculations. In contrast with repeated decelerations, when fetal hypoxia is considered evident, the place of the software analysis of the fetal heart rate variability is less clear. Although the advantages of mathematized and uniform quantification of the fetal heart rate variability appear self-evident, there are no studies with sufficient power to detect an association of intervention based on STV at any threshold with the most important outcomes: fetal death and long-term infant outcome.

The purpose of this study is to assess the outcomes of monitoring the fetal condition with STV in computerized CTG compared to visual interpretation of the CTG in order to time delivery in pregnant women with severe, early-onset FGR.

Inclusion criteria

• Pregnant women with a singleton pregnancy between 24 weeks and 0 days and 31 weeks and 6 days with severe, early-onset fetal growth restriction, admitted in hospital or frequently evaluated ambulatory by CTG (according to local protocol) for fetal monitoring.
• Fetal growth restriction is defined in line with the international Delphi consensus as biometric ultrasound measurement of the abdominal circumference (AC) OR a combination of measurements resulting in an estimated fetal weight (EFW) below the 3rd percentile (<p3) OR a combination of EFW <p10 AND uterine artery pulsatility index (PI) >p95 OR umbilical artery Doppler PI >p95.
• Maternal age ≥ 18 years.
• Able to provide written informed consent for collection and use of data on informed consent form in available language.

Exclusion criteria

• Known congenital or chromosomal anomalies influencing perinatal outcome.
• Imminent labour or expected maternal indication for delivery < 48 hours.