Ultrasound screening protocol for monitoring monochorionic multifetal pregnancies

Gestational age	Purpose of ultrasound examination and frequency
11 to 14 weeks	One examination for: Assessment of gestational age and estimated date of delivery Assessment of chorioamnionicity Measurement of nuchal translucency*
16 AND 18 weeks	Fetal size Early fetal anatomic survey, including presence and size of fetal bladders MVP of amniotic fluid Doppler measurement of MCA-PSV Doppler measurement of end-diastolic velocity in the UA Assessment for PDE
20 weeks	Fetal size Detailed fetal anatomic survey, including presence and size of fetal bladders MVP Doppler measurement of MCA-PSV Doppler measurement of UA end-diastolic flow velocity PDE Evaluate placental cord insertion sites (proximate cord insertion is defined by a distance between cord insertions below the fifth percentile for gestational age or by 3.3 to 4.0 cm at any gestational age)
20 to 22 weeks	Transvaginal ultrasound measurement of cervical length Fetal echocardiogram
22 to 32 weeks	Serial examinations of fetal growth every 4 weeks Serial examinations of the following every 2 weeks: MVP Presence and size of fetal bladders Doppler measurement of MCA-PSV Doppler measurement of UA end-diastolic flow velocity PDE
32 to 36 weeks	Continue serial examinations of fetal growth every 4 weeks Weekly examinations: Biophysical profile score Doppler measurement of MCA-PSV Doppler measurement of UA end-diastolic flow velocity PDE

MVP: maximum vertical pocket; MCA: middle cerebral artery; PSV: peak systolic velocity; UA: umbilical artery; PDE: placental discordance echogenicity.
* Increased nuchal translucency has been associated with trisomy 21, a variety of congenital anomalies, developmental and genetic syndromes, and twin-twin transfusion syndrome. Refer to UpToDate content on cystic hygroma and increased nuchal translucency.

Modified from:

Khalil A, Rodgers M, Baschat A, et al. ISUOG Practice Guidelines: role of ultrasound in twin pregnancy. Ultrasound Obstet Gynecol 2016; 47:247.
Society for Maternal-Fetal Medicine, Simpson LL. Twin-twin transfusion syndrome. Am J Obstet Gynecol 2013; 208:3.
Sueters M, Middeldorp JM, Lopriore E, et al. Timely diagnosis of twin-to-twin transfusion syndrome in monochorionic twin pregnancies by biweekly sonography combined with patient instruction to report onset of symptoms. Ultrasound Obstet Gynecol 2006; 28:659.

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Ultrasound screening protocol for monitoring monochorionic multifetal pregnancies