ACR Appropriateness Criteria ® Multiple Gestations

Abstract

Women with twin or higher-order pregnancies will typically have more ultrasound examinations than women with a singleton pregnancy. Most women will have at minimum a first trimester scan, a nuchal translucency evaluation scan, fetal anatomy scan at 18 to 22 weeks, and one or more scans in the third trimester to evaluate growth. Multiple gestations are at higher risk for preterm delivery, congenital anomalies, fetal growth restriction, placenta previa, vasa previa, and velamentous cord insertion. Chorionicity and amnionicity should be determined as early as possible when a twin pregnancy is identified to permit triage of the monochorionic group into a closer surveillance model. Screening for congenital heart disease is warranted in monochorionic twins because they have an increased rate of congenital cardiac anomalies. In addition, monochorionic twins have a higher risk of developing cardiac abnormalities in later gestation related to right ventricular outflow obstruction, in particular the subgroups with twin-twin transfusion syndrome or selective intrauterine growth restriction. Monochorionic twins have unique complications including twin-to-twin transfusion syndrome, twin embolization syndrome, and acardius, or twin-reversed arterial perfusion sequence. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Early Pregnancy Ultrasound Assessment of Multiple Pregnancy

“…This is well-established since it is known that the differentiation of a yolk sac and an amnion occur very close to each other in time, around 6-8 days after fertilization [5]. If a single yolk sac is detected, a repeat first trimester scan is undertaken, or a refer to a tertiary center with advanced experience in multiple pregnancies can be helpful [3,4].…”

“…Salomon et al [13] suggested that the CRL of the smallest fetus can estimate more accurately the gestational age, if the intertwin CRL discrepancy is less than the 95th percentile, using charts from studies. An interesting finding is that if the intertwin discordance in CRL is higher than 10%, the possibility of pregnancy loss, aneuploidy, or congenital anomalies is increased [3,14,15].…”

“…The evaluation of the amnion should be done diligently via transvaginal ultrasound since the intertwin membrane is extremely thin and it may be invisible via transabdominal ultrasound. Even when the separate amnions cannot be visualized via the transvaginal ultrasound, their absence can be confirmed by demonstrating umbilical cord enlargement by using pulsed wave Doppler and identifying two distinct heart rates [3]. In addition, the impossible visualization of the intertwin membrane may be technical: if the membrane is parallel to the ultrasound beam or because the ultrasound gain is low, the membrane may be hard to evaluate.…”

“…In fact, twins comprise about 3% of all live births in the United in the past were diagnosed during the intrapartum period [2]. Today, as the use of ultrasound has become a routine in daily medical practice, multiple pregnancies are diagnosed in the initial ultrasound scan [3]. Beyond the diagnosis of early multiple pregnancy, ultrasound scan is more than necessary to define chorionicity, amnionicity, and gestational age [4].…”

“…Chorionicity and amnionicity are differentiated by the timing of embryo splitting. Table 1 presents this differentiation and the frequency of each type of a monozygotic pregnancy [3].…”