![]() ![]() ![]() Future well‐designed studies could also research the impact of whether the babies share a placenta (or not), the sex of the babies, and gestational age (time from woman's last menstrual period), in the diagnostic accuracy of ultrasound for estimated birth weight differences.īirth weight discordance (BWD), defined as a difference in the birth weights of twins, is a well‐documented phenomenon in twin pregnancies ( Bagchi 2006 Mahony 2006). The diagnostic accuracy of other measures including amniotic fluid volume (the fluid surrounding the babies in the womb) or Doppler studies (which use sound waves to detect the movement of blood in the babies' blood vessels and the umbilical cord) in combination with ultrasound to inform clinical decisions needs to be evaluated. There is insufficient evidence to support the use of ultrasound as the sole measure for detecting birth weight differences in twins, or poor outcomes. On average, ultrasound detected birth weight differences of 20% and 25% only half the time. We found that ultrasound estimation of fetal weight differences compared to birth weight differences was not reliable. We assessed the quality of individual studies using a tool called "Quality Assessment of Diagnostic Accuracy Studies" (QUADAS‐2) and the overall quality by a recommended method called GRADE to find out the reliability of the evidence. Twenty‐two studies provided data on birth weight differences of 20% and 18 studies provided data on birth weight differences of 25%. We searched medical databases to March 2019 for studies comparing ultrasound measurements to birth weight differences and we identified 39 studies. In this review, we summarized data on whether the ultrasound measurements are accurate enough to predict birth weight differences in twins. Clinicians measure the estimated fetal weight differences by ultrasound before birth and compare it to differences in birth weight after the babies are born. Ultrasound during pregnancy for predicting differences in birth weight between twinsīirth weight differences of more than 20% in twins is associated with poor outcomes for the mother and baby. Subgroup analyses were not possible by sex of twins, chorionicity or gestational age due to insufficient data. The diagnostic accuracy did not differ substantially between estimation by abdominal circumference and femur length but femur length had a trend towards higher sensitivity and specificity. Subgroup analyses were possible for both BWD of 20% and 25%. ![]() The summary estimate of sensitivity was 0.46 (95% CI 0.26 to 0.66), and the summary estimate of specificity was 0.93 (95% CI 0.89 to 0.96) (6471 twin pregnancies very low‐certainty evidence). Ultrasound for diagnosis of BWD in twin pregnancies at 25% cut‐offĮighteen studies provided data using a BWD discordance of 25%. Twenty‐two studies provided data for a BWD of 20% and the summary estimate of sensitivity was 0.51 (95% CI 0.42 to 0.60), and the summary estimate of specificity was 0.91 (95% CI 0.89 to 0.93) (8005 twin pregnancies very low‐certainty evidence). Ultrasound for diagnosis of BWD in twin pregnancies at 20% cut‐off In terms of applicability, most studies were of low concern. Twenty‐one studies (53%) were of methodological concern due to flow and timing. In terms of risk of bias, there were many unclear statements regarding patient selection, index test and use of proper reference standard. We included 39 eligible studies with a median study sample size of 140. ![]()
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