The clinical prognosis of single and double velvet twins is significantly different, and single plush twins are more likely to have fetal complications, so the frequency of prenatal ultrasound monitoring is not the same.
Double chorionic twin pregnancies without comorbidities should be tested for first trimester ultrasound, that is, NT examination at 11-14 weeks, to determine the gestational age, to clarify chorionicity, to carry out twin marking, etc., to 20-22 weeks for fetal malformation screening, biological measurement, amniotic fluid measurement and cervical length measurement, etc., after which if there is no special situation, the interval can be 4 weeks, that is, 24-26 weeks, 28-30 weeks, 32-34 weeks, 36-37 weeks for fetal growth assessment, Amniotic fluid measurement and fetal blood flow Doppler assessment, etc. (see Figure 1 for details). Dual chorionic twin pregnancies with comorbidities undergo more frequent ultrasounds and more surveillance depending on the specificity and severity of the disease.
Fig. 1 Ultrasound monitoring pathway for double-velvet twins without comorbidities
In addition to first-trimester (11-14 weeks) ultrasound, single-chorionic twins without comorbidities are recommended to be performed every 2 weeks starting at 16 weeks of pregnancy in order to detect twin transfusion syndrome and twin anemia sequence signs of erythrocytosis in time. Fetal growth assessment, amniotic fluid measurement, and fetal umbilical artery blood flow assessment are performed at 16 and 18 weeks, fetal structural malformation screening, fetal growth assessment, amniotic fluid measurement, fetal umbilical artery and middle cerebral artery blood flow assessment, and cervical length measurement are performed at 2 weeks thereafter, fetal growth assessment, amniotic fluid measurement, fetal umbilical artery blood flow, and middle cerebral artery blood flow assessment are performed every 2 weeks until 36 weeks (see Figure 2 for details). Single-chorionic twin pregnancies with comorbidities undergo more frequent ultrasounds and more surveillance depending on the specificity and severity of the disease.
Fig. 2 Single-velvet twin ultrasound monitoring pathway without comorbidities
参考文献：Khalil A, Rodgers M, Baschat A, et al. ISUOG Practice Guidelines: role of ultrasound in twin pregnancy [J]. Ultrasound Obstet Gynecol, 2016, 47(2): 247-263.
Reference source: Department of Obstetrics and Gynecology, Xi'an Jiaotong No.1 Affiliated Hospital
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