Strengths and limitations
To the authors’ knowledge, this is the first UK-wide study of sIUFD in MC twin pregnancies. A major strength of this study is that data were collected from UK centres, thus the results represent current UK-wide practice. UKOSS is a validated mechanism of collecting data on relatively rare conditions that is UK wide. Data collection relies on a system of designated clinician data collectors. In this study there were 8 cases for whom outcome data was missing following fetal therapy at a tertiary centre. This is in contrast to the only other UKOSS study relating to a fetal condition, gastroschisis, where there were no missing outcome data. This difference might reflect the complexity of complicated MC twins requiring management at multiple care providers (supraregional, regional and local), and that within the gastroschisis study outcome data was also collected via paediatric surgeons and via cross-checking with congenital anomaly registers. One of the difficulties of data collection in complex conditions is a lack of standard pathways of care and definitions of outcomes (e.g. ultrasound findings). This is especially true for the complex conditions complicating MC pregnancies, where each fetus maybe affected differently. Since data collection for this study there have been initiatives to guide the management of these complex pregnancies, and define outcomes 19, 20and within the UK specialist fetal medicine commissioning will improve pathways of care.
The number of cases notified was considerably lower than our pre-study estimate. However, MBRRACE-UK data (national surveillance of perinatal deaths) in 2016, noted perinatal mortality rates amongst twins as the lowest ever reported21, 22 and thus we employed triangulation of data with MBRACCE-UK to check case ascertainment. Using ONS data23 and MBRACCE data21, and newer evidence to suggest that 20% of twins are monochorionic24, 25 (as opposed to the 30% of our original estimate), we calculated incidence of single twin demise across the 2 years of our study. This gives very similar figures of an estimated 75 cases in 2016 and 84 in 2017 with incidence of 37.6-38.7 per 1000 monochorionic maternities. A further strength of this study was the collection of data relating to interventions, management and outcomes for both mother and neonate. It is not possible to collect data for the baby via the UKOSS system past the point of discharge from hospital after birth. Further studies and research in this area should include data related to longer term outcomes for the baby7.