Chorionicity
The number of chorionic plate (placentas). It may be dichorionic, monochorionic, monoamniotic and, rarely, conjoined.
Delayed Interval Delivery (DID)
The procedure where delaying the delivery of a second foetus in a twin pregnancy is pursued after delivery of the first foetus during very early preterm birth (< 28 weeks).
Selective Foetal Growth Restriction (sFGR)
Expected foetal weight (EFW) < 10th percentile in one foetus or a difference in EFW > 25 % between the twins, is a pathophysiological distinct process in monochorionic twins and influenced by the division of the placenta between the foetuses and the type of vascular anastomoses.
Single Intrauterine Foetal Death (sIUFD)
The death of one or both twins (double IUFD). The challenge with sIUFD occurring in twins concerns the effect on the surviving co-twin.
Twin Anaemia Polycythaemia Sequence (TAPS)
The occurrence of significant haemoglobin discordancy in a monochorionic pair in the absence of the amniotic fluid discordance needed for diagnosing TTTS.
Twin Reversed Arterial Perfusion (TRAP)
A specific abnormal development of monochorionic twins characterised by an abnormal foetus that grows but has no functional cardiac activity of its own.
Twin-Twin Transfusion Syndrome (TTTS)
A chronic imbalance in inter-foetal transfusion across the existing vascular anastomoses in monochorionic twins, resulting in hydramnios secondary to polyuria (recipient), combined with oligohydramnios in secondary to oliguria (donor).
Zygoty
The fertilisation of a single egg (monozygoty) or fertilisation of different eggs after polyovulation (polyzygoty).
