Chorionicity ultrasound
A chorionicity ultrasound is used to distinguish between twins that share a placenta and those who have separate ones, so that twins at higher risk of complications can be monitored more closely.
- determine chorionicity and amnionicity at the time of detecting a twin or triplet pregnancy by ultrasound using:
- the number of placental masses
- the presence of amniotic membrane(s) and membrane thickness
- the lambda or T-sign
- if a woman with a twin or triplet pregnancy presents after 14+0 weeks, determine chorionicity and amnionicity at the earliest opportunity by ultrasound using all of the following:
- the number of placental masses
- the presence of amniotic membrane(s) and membrane thickness
- the lambda or T-sign
- discordant fetal sex
Chorionicity:
- number of chorionic (outer) membranes that surround babies in a multiple pregnancy
- If there is only 1 membrane, the pregnancy is described as monochorionic;
- if there are 2, the pregnancy is dichorionic; and
- if there are 3, the pregnancy is trichorionic
- monochorionic twin pregnancies and monochorionic or dichorionic triplet pregnancies carry higher risks because babies share a placenta
Reference:
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