Validity of sonographic prediction of fetal weight and weight discordance in twin pregnancies

Introduction

Ultrasonography is an essential tool in the management of twin pregnancies. Fetal weight estimation is useful to anticipate neonatal care in case of prematurity, growth restriction or growth discordance.

Objective 

The aims of this study were (1) to assess the accuracy of estimated fetal weight (EFW) in twins and (2) to assess the accuracy of sonographic examination to predict birth weight discordance (BWD)

Methods

All twin pregnancies with at least one ultrasound (US) examination within 04 days of delivery were included in this study. EFW was calculated according Hadlock2 formula. Mean of the standardized errors and percentage of newborns with birth weight (BW) within 10% of EFW were calculated.

Results

Absolute differences between EFW and BW were similar for both twins (187 g [0–850] for T1 and 156 g [0–600] for T2).
Mean absolute percentage error was 7.7% (0-32gr) for T1 and 8.2% (0-27gr) for T2.
Mean absolute percentage error was superior to 10% for 42% of T1 and 46% of T2 with no significant difference.
Obesity were associated with a better accuracy of ultrasonography
Chorionicity, gestational age as well as fetal presentation did not influence fetal weight estimation
Ultrasonography in the diagnosis of hypotrophy had a sensitivity of 90.32%, a specificity of 78.94%, a positive predictive value (PPV) of 83.5% and a negative predictive value (NPV) of 87.5%. For the prediction of growth discordance, sensitivity was 76.9%, specificity 81.8%, PPV 50% and NPV 93.5%.

Conclusion 

Sonographic prediction of inter-twin BWD within four days of delivery seems to be accurate enough for routine clinical use. Performance and predictive values depend on the threshold chosen to define
EFW and BW discordance.

Keywords

Twins, discordance, weight