Chorionicity – How many placentas.
Amnionicity – How many amniotic sacs.
Determination of amnionicity and chorionicity is critical in the antenatal management of twins and should be done in the first trimester.
Chorionicity is important for managing structural anomalies, aneuploidy, the aetiology of fetal growth and/or fluid discordance, early diagnosis of twin-to-twin transfusion syndrome, and the management of a surviving twin following intrauterine demise.
There is a high mortality and morbidity of monoamniotic twins.
- Monochorionic means 1 shared placenta.
- Dichorionic means 2 placentas (twins/triplets).
- Trichorionic means 3 placentas (triplets) and so on.
The amnion may be around 1 of the fetuses or there may be a second or third foetus within the same amniotic sac. It is important to turn the gain up to see if there is a thin membrane between the fetuses.