Can be identical (monozygotic) or non-identical (dizygotic)
- Monochorionic monoamniotic
- monochorionic diamniotic
- dichorionic diamniotic (best outcomes)
Diagnosis
Multiple pregnancy is usually diagnosed on the booking ultrasound scan. Ultrasound is also used to determine the:
- Gestational age
- Number of placentas (chorionicity) and amniotic sacs (amnionicity)
- Risk of Down’s syndrome (as part of the combined test)
When determining the type of twins using an ultrasound scan:
- Dichorionic diamniotic twins have a membrane between the twins, with a lambda sign or twin peak sign
- Monochorionic diamniotic twins have a membrane between the twins, with a T sign
- Monochorionic monoamniotic twins have no membrane separating the twins
Complications
Risks to the mother: