Perinatal Outcomes of Small for Gestational Age in Twin Pregnancies: Twin vs. Singleton Charts

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.

Adverse neonatal outcome in twin pregnancy complicated by small‐for‐gestational age: twin vs singleton reference charts

“…Our findings suggest that, compared with singleton charts, twin-specific charts can identify more accurately those infants who are at the highest risk of developing adverse neonatal outcome. This superior accuracy of twin charts has also been demonstrated in previous studies investigating other perinatal outcomes and neonatal mortality 1,21,22 . Our previous study identified that twin-specific charts also outperformed singleton charts in the prediction of abnormal fetal Doppler parameters 21 , suggesting that the twin charts are better at identifying fetal growth restriction and might therefore be expected to correlate better with adverse perinatal outcome.…”

“…This superior accuracy of twin charts has also been demonstrated in previous studies investigating other perinatal outcomes and neonatal mortality 1,21,22 . Our previous study identified that twin-specific charts also outperformed singleton charts in the prediction of abnormal fetal Doppler parameters 21 , suggesting that the twin charts are better at identifying fetal growth restriction and might therefore be expected to correlate better with adverse perinatal outcome. In this study, we have shown that twin charts are better than singleton charts at identifying twins at increased risk of neonatal morbidity and mortality.…”

Controversies in the management of twin pregnancy

“…The study concluded that the use of singleton charts was associated with misclassification of a large number of twins as at risk of FGR 31 . Therefore, twin-specific charts could reduce unnecessary medical interventions prenatally and postnatally.…”

“…It has been shown that use of these charts does not increase the incidence of stillbirth, but does in fact reduce the number of twins diagnosed as FGR compared to customized singleton charts (7.1% vs 12.8%) 30 . Moreover, a recent study which investigated the risk of perinatal mortality, preterm birth, hypertensive disorders of pregnancy and admission to the neonatal unit in twins according to whether classification as small‐for‐gestational age (SGA) was determined using singleton or twin charts demonstrated that twins classified as SGA according to the singleton charts but not according to the twin charts had similar outcomes to twins classified as appropriate‐for‐gestational age 31 . The study concluded that the use of singleton charts was associated with misclassification of a large number of twins as at risk of FGR 31 .…”

“…Moreover, a recent study which investigated the risk of perinatal mortality, preterm birth, hypertensive disorders of pregnancy and admission to the neonatal unit in twins according to whether classification as small‐for‐gestational age (SGA) was determined using singleton or twin charts demonstrated that twins classified as SGA according to the singleton charts but not according to the twin charts had similar outcomes to twins classified as appropriate‐for‐gestational age 31 . The study concluded that the use of singleton charts was associated with misclassification of a large number of twins as at risk of FGR 31 . Therefore, twin‐specific charts could reduce unnecessary medical interventions prenatally and postnatally.…”