UKOSS Single intrauterine fetal death in monochorionic twins study: incidence; maternal, fetal and neonatal consequences (single twin demise in monochorionic twins)
Dr Katie Morris

Monochorionic twins (20-30% of twin pregnancies) share the same placenta and blood flow between them which puts them at high risk of pregnancy complications, including miscarriage and stillbirth. One of these complications is single intrauterine fetal death (single twin demise) whereby one of the twins dies whilst still in the womb, and this affects between 2.6-6.2% of all twin pregnancies.

When this happens before 14 weeks it is described as a ‘vanishing twin’ and although it may have a psychological effect on the parents, it does not have a negative effect on the pregnancy. However, when one baby dies after 14 weeks this can have serious implications for the remainder of the pregnancy and can lead to poor outcomes for the other baby. There may also be an impact on the mother such as pre-eclampsia (high blood pressure in pregnancy).

Professor Mark Kilby

Unfortunately, doctors do not know how high the risk of these serious problems is and how best to manage a pregnancy after one of the babies has sadly died. Doctors at the University of Birmingham (Dr Katie Morris and Professor Mark Kilby), in collaboration with the UK Obstetric Surveillance System (UKOSS), asked all doctors across the UK to report cases in 2016-17 where one baby died and let the researchers know the details of the pregnancy and outcome. The research’s aim was to find out how common single twin demise is in the UK; what is unique about pregnancies affected by single twin demise; current antenatal care/interventions used to manage these pregnancies; the effect on the mother and babies before and after birth; and if there are any signs that might predict single twin demise.  This research will enable clinicians to give better advice to women in the future, and improve the care and outcome of these pregnancies.

The study found that:

  • monochorionic twin pregnancies where one baby dies are complex and require specialist care;
  • further research is required to determine when is the best time to deliver the surviving co-twin, how and when to intervene to prevent preterm birth, and what the cause of death is in twin pregnancies;
  • awareness of the importance of central nervous system imaging, and follow-up, needs improvement.
Professor Marion Knight

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This study was carried out by Dr Katie Morris and Professor Mark Kilby at the University of Birmingham, and Professor Marian Knight at the University of Oxford, and was funded by the Twins Trust and BMFMS research bursaries.