Case definition
All MC twin pregnancies with a sIUFD after 14 weeks gestation, including
spontaneous IUFD (i.e. no signs of TTTS, sIUGR or congenital/structural
anomaly), IUFD after intervention for complications such as fetoscopic
laser ablation (FLA) for TTTS, sIUGR or selective feticide (intrafetal
laser, radiofrequency ablation and cord occlusion) were included. Those
with “major” structural fetal anomalies (concordant and discordant)
were included, as were MC monoamniotic twins. For inclusion,
chorionicity had to have been confirmed in the first trimester based on
the presence of the ’T’ sign and absence of the ‘lambda’ sign, and a
single placental mass13-15. The following were
excluded: higher order multiples where fetal reduction had been
performed, pregnancies with twin reversed arterial perfusion sequence.
TTTS was defined according to the Quintero
definition16, and sIUGR as an inter-twin growth
discordance greater than 20% in estimated fetal weights as at the time
of designing the study there were no validated twin-specific growth
charts.