Optimal Interval between Ultrasound Scans for the Detection of Complications in Monochorionic Twins

Monochorionic-diamniotic (MCDA) twin pregnancies are high risk, due to twin-to-twin transfusion syndrome (TTTS), twin anaemia polycythaemia sequence (TAPS) and intrauterine growth restriction (IUGR). There is limited evidence to guide ultrasound surveillance protocols. Using a retrospective cohort, we aimed to provide insight into the optimal interval of ultrasound surveillance.

Retrospective cohort of women with MCDA pregnancies who received antenatal care at Monash Medical Centre (January 2011-October 2014). We reviewed all ultrasounds from ≥15 weeks' gestation and collected perinatal outcomes.

A total of 162 women with MCDA pregnancies attended our care. Six women were excluded due to late referral. Of the remaining 156, 55% were uncomplicated. TTTS, TAPS, IUGR and fetal demise in utero occurred in 9%, 1%, 31% and 2%, respectively. Median interval between the last ultrasound and TTTS diagnosis was 3.1 weeks (IQR 0.8-5.8). There was a trend towards a longer interval for cases with advanced TTTS compared to early TTTS. Interval between ultrasound scans was longer in cases with unexplained fetal demise in utero and advanced TTTS than early TTTS [3.4 weeks (IQR 2.0-6.9) vs. 0.9 weeks (IQR 0.4-3.7); p < 0.05].

Our observations support current recommendations for fortnightly ultrasound surveillance in MCDA pregnancies from 16 weeks' gestation and suggest that longer intervals may be associated with poorer outcomes.