Twin birth weight discordance is associated with poor perinatal outcome. Three cases of severe discordant twins were serially assessed by ultrasound biometry and the Doppler ultrasonography of both the middle cerebral artery (MCA) and umbilical artery (UA) to measure pulsatility index (PI), resistance index (RI), and the systolic and diastolic ratio (S/D ratio). The birth weight discrepancies in three cases are 38%, 69% and 68%, respectively. Doppler velocimetry revealed a discrepancy in the S/D ratio of MCA and UA more than 15%. Absent end-diastolic flow, or the brain sparing effect, was noted in three small twins. Cerebral-umbilical S/D ratio (CUR) (MCA/UA) of the twins was above 1 in large ones and below 1 in small ones. The small twin in case 3 expired after delivery. In conclusion, if the CUR of the S/D ratio of the fetus is below 1, the prognosis might be poor and fetal weight discordancy might be progressively larger.
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