Introduction
Monochorionic (MC) twin pregnancies constitute approximately 30% of all
twin pregnancies and are complex due to the conjoining of the two fetal
circulations by placental vascular anastomoses, predisposing the
pregnancies to unique complications, including twin-twin transfusion
syndrome (TTTS), selective intrauterine growth restriction (sIUGR), and
single intrauterine fetal death (sIUFD)1, 2 . Data
from cohort studies and case series indicate that sIUFD complicates up
to 6% of all twin pregnancies (although the true prevalence is
unknown)3 . sIUFD occurs more frequently in MC twins
(7.5%) compared to dichorionic twins (3%)4 with
morbidity affecting the surviving fetus being higher in MC
twins3 . Many sIUFDs occur before 14 weeks gestation
presenting at a dating ultrasound scan as a ‘vanishing’ twin. However
sIUFDs after 14 weeks are potentially associated with serious perinatal
consequences for the surviving co-twin including IUFD (i.e. after death
of the first twin), preterm birth, long-term neurological comorbidity,
and neonatal death 5-7. Additionally, maternal
morbidity following sIUFD has been reported with higher rates of
pre-eclampsia, coagulopathy and sepsis8, 9.
Clinical management is challenging as controversy exists relating to
optimal time of delivery, frequency of prenatal ultrasound surveillance
and appropriate investigations to determine central nervous system
imaging (CNS) morbidity10, 11. In addition, the
maternal and paternal psychological effects of such a complication may
be profound. We have previously published three systematic reviews
investigating the outcomes of the surviving co-twin following
sIUFD5, 7, 12; despite an additional 20 studies being
able to be included in the most contemporary review and reduced
heterogeneity, the same issue of small study bias persisted. Although
there appeared to be an emerging consistency within the international
literature supporting ‘conservative management’, there was little
objective evidence as to: a) most reliable method of assessing fetal
wellbeing, b) the use of prenatal imaging to identify CNS damage (i.e.
ultrasound vs. Magnetic Resonance Imaging [MRI] or a combination),
c) optimal gestation and mode of delivery.
The objectives of this study were to report on the incidence of, and
maternal, fetal and neonatal complications associated with sIUFD (after
14 weeks gestation) in MC twin pregnancies in the United Kingdom. These
data are important to: improve counselling of parents regarding the
prognosis of the surviving co-twin, and aid management decisions.