Abstract
Twin pregnancies are commonly assessed using singleton growth and birth weight reference charts. This practice has led to a significant number of twins labelled as small for gestational age (SGA), causing unnecessary interventions and increased risk of iatrogenic preterm birth. However, the use of twin-specific charts remains controversial. This study aims to assess whether twin-specific estimated fetal weight (EFW) and birth weight (BW) charts are more predictive of adverse outcomes compared to singleton charts. Centiles of EFW and BW were calculated using previously published singleton and twin charts. Categorical data were compared using Chi-square or McNemar tests. The study included 1740 twin pregnancies, with the following perinatal adverse outcomes recorded: perinatal death, preterm birth <34 weeks, hypertensive disorders of pregnancy (HDP) and admissions to the neonatal unit (NNU). Twin-specific charts identified prenatally and postnatally a smaller proportion of infants as SGA compared to singleton charts. However, twin charts showed a higher percentage of adverse neonatal outcomes in SGA infants than singleton charts. For example, perinatal death (SGA 7.2% vs. appropriate for gestational age (AGA) 2%, p < 0.0001), preterm birth <34 weeks (SGA 42.1% vs. AGA 16.4%, p < 0.0001), HDP (SGA 21.2% vs. AGA 13.5%, p = 0.015) and NNU admissions (SGA 69% vs. AGA 24%, p < 0.0001), when compared to singleton charts (perinatal death: SGA 2% vs. AGA 1%, p = 0.029), preterm birth <34 weeks: (SGA 20.6% vs. AGA 17.4%, p = 0.020), NNU admission: (SGA 34.5% vs. AGA 23.9%, p < 0.000). There was no significant association between HDP and SGA using the singleton charts (p = 0.696). In SGA infants, according to the twin charts, the incidence of abnormal umbilical artery Doppler was significantly more common than in SGA using the singleton chart (27.0% vs. 8.1%, p < 0.001). In conclusion, singleton charts misclassify a large number of twins as at risk of fetal growth restriction. The evidence suggests that the following twin-specific charts could reduce unnecessary medical interventions prenatally and postnatally.
Highlights
estimated fetal weight (EFW) less than 10th centile using a singleton chart was significantly associated with the risk of adverse outcomes
Our results reveal a similar trend, suggesting that small for gestational age (SGA) defined using twin-specific charts, both EFW and birth weight (BW), had a stronger association between those labelled as SGA and those at risk of adverse outcomes
Our study suggests that using twin-specific EFW and BW charts significantly reduces the proportion of twins classified as SGA
Summary
An important element of twin surveillance includes monitoring to identify fetal growth restriction (FGR), as evidence suggests that growth-restricted infants are at increased risk of adverse perinatal outcomes, including increased mortality and morbidity [4]. Vital to accurately assess the growth of twins antenatally and postnatally, to identify those who would benefit from preterm birth, altered surveillance and neonatal interventions. It is currently a routine practice to assess both the antenatal growth and postnatal birthweight of twins using singleton estimated fetal weight (EFW) and birth weight (BW)
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