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.