Statistics
The incidence of sIUFD in MC twin pregnancy was planned to be calculated
using ONS data as the denominator. Maternal, fetal and neonatal outcomes
were described and reported as percentages, mean and SDs or medians and
IQRs as appropriate. Sub-group analyses were planned to determine if
TTTS or sIUGR, were associated with any characteristics, or if they were
associated with a poorer outcome for the surviving co-twin. We also
planned to explore prognostic indicators for mother and infant
associated with sIUFD in MC twin pregnancy, e.g. gestation of IUFD of
the first twin, using logistic regression. No sample size calculation
was performed, but prior to commencing the study, we had estimated,
based on ONS data from 2012 and existing literature, that of 11,228 twin
pregnancies, 30% would be MC, and 7.5% would result in a sIUFD, thus
there would be 253 cases per annum. No imputations of missing data were
performed, cases with missing outcomes were not included in certain
analyses as stated below. The study is funded by the British
Maternal Fetal Medicine Society and Twins Trust (formerly
TAMBA).