3. Results
A total of 4055 pregnancy women, 2142 singleton vs. 1913 twin, were
recruited in this study. The flowchart of twin participants enrollment
was shown in Figure 1 (The enrollment flowchart for singleton
participants is very similar and not shown). The final sample consisted
of 2019 singleton, alongside with a total of 9787 ultrasound
observations, and 929 mothers (148 SC-MCDA, 215 SC-DCDA and 566
ART-DCDA), alongside with a total of 12837 ultrasound observations (3099
in 296 SC-MCDA, 2542 in 430 SC-DCDA and 7196 in 1132 ART-DCDA fetuses).
A gestational age interval between 14 and 37 weeks was covered.