If there is an intertwin discrepancy in CRL or NT measurements, this may be an early marker for TTTS [9]. US Cervix Transvaginal Transvaginal US (TVUS) of the cervix can be performed to confirm that the cervix is closed and is done along with TVUS of the pregnant uterus. An open cervix indicates a high risk for miscarriage. Cervical length measurement is not recommended in the first trimester. In studies specifically evaluating twin pregnancies, routine TVUS assessment of cervical length in the first trimester (as a component of standard management of low-risk twins) has not been shown to predict preterm labor or to be associated with improved outcomes [25,26]. In an asymptomatic and low-risk twin population, a single transvaginal cervical length between 16 and 20 weeks was not predictive of spontaneous preterm birth before 34 weeks, and hence cervical length measurement in the first trimester is of limited value [25,26]. US Duplex Doppler Fetal Middle Cerebral Artery US Doppler of the fetal MCA is not useful as an initial imaging modality for the evaluation of known or suspected multiple gestations. Fetal organogenesis is usually completed by 11 to 12 weeks, at which time identifiable fetal anatomic parts have developed. Until organogenesis completion around 12 weeks, a separate fetal MCA is not identifiable, and hence fetal MCA Doppler cannot be performed. Hence, this examination is not useful in the first trimester. US Duplex Doppler Fetal Umbilical Artery US duplex Doppler of the fetal UA is not useful as an initial imaging modality for the evaluation of known or suspected multiple gestations [9]. In the early first trimester, an identifiable UA cannot reliably be assessed. An identifiable UA is present in the late first trimester; however, there is still no role for UA assessment in the first trimester [9]. US Echocardiography Fetal US echocardiography has no role in the initial imaging in the first trimester [9].
Multiple Gestations. If there is an intertwin discrepancy in CRL or NT measurements, this may be an early marker for TTTS [9]. US Cervix Transvaginal Transvaginal US (TVUS) of the cervix can be performed to confirm that the cervix is closed and is done along with TVUS of the pregnant uterus. An open cervix indicates a high risk for miscarriage. Cervical length measurement is not recommended in the first trimester. In studies specifically evaluating twin pregnancies, routine TVUS assessment of cervical length in the first trimester (as a component of standard management of low-risk twins) has not been shown to predict preterm labor or to be associated with improved outcomes [25,26]. In an asymptomatic and low-risk twin population, a single transvaginal cervical length between 16 and 20 weeks was not predictive of spontaneous preterm birth before 34 weeks, and hence cervical length measurement in the first trimester is of limited value [25,26]. US Duplex Doppler Fetal Middle Cerebral Artery US Doppler of the fetal MCA is not useful as an initial imaging modality for the evaluation of known or suspected multiple gestations. Fetal organogenesis is usually completed by 11 to 12 weeks, at which time identifiable fetal anatomic parts have developed. Until organogenesis completion around 12 weeks, a separate fetal MCA is not identifiable, and hence fetal MCA Doppler cannot be performed. Hence, this examination is not useful in the first trimester. US Duplex Doppler Fetal Umbilical Artery US duplex Doppler of the fetal UA is not useful as an initial imaging modality for the evaluation of known or suspected multiple gestations [9]. In the early first trimester, an identifiable UA cannot reliably be assessed. An identifiable UA is present in the late first trimester; however, there is still no role for UA assessment in the first trimester [9]. US Echocardiography Fetal US echocardiography has no role in the initial imaging in the first trimester [9].