Multiple pregnancy

• Monozygotic = identical twins (from single zygote)

  
  

  Dizygotic = non-identical
• Monoamniotic = single amniotic sac

  Diamniotic = two separate amniotic sacs
• Monochorionic = share a single placenta

  Dichorionic = two separate placentas
• The best outcomes are with diamniotic, dichorionic twin pregnancies, as each fetus has their own nutrient supply.
• 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
• Lambda/twin peak sign:

  • Triangular appearance where the membrane between the twins meets the chorion (placenta), as the chorion blends partially into the membrane
  • Indicates a dichorionic twin pregnancy (separate placentas)
• The T sign refers to where the membrane between the twins abruptly meets the chorion, giving a T appearance. This indicates a monochorionic twin pregnancy (single placenta).
• Risks to the mother:

  • Anaemia
  • Polyhydramnios
  • Hypertension
  • Malpresentation
  • Spontaneous preterm birth
  • Instrumental delivery or caesarean
  • Postpartum haemorrhage
• Risk to the foetus and neonates:

  • Miscarriage
  • Stillbirth
  • Fetal growth restriction
  • Prematurity
  • Twin-twin transfusion syndrome
  • Twin anaemia polycythaemia sequence
  • Congenital abnormalities
• Twin-twin transfusion syndrome:

  • when they share a placenta
  • One foetus (recipient) may receive the majority of the blood, while the other (donor) is starved of blood
  • The recipient can become fluid overloaded with heart failure and polyhydramnios
  • The donor has growth restriction, anaemia and oligohydramnios
  • Need to be referred to specialist foetal medicine centre
  • Laser treatment may be used to destroy the connection between the two blood supplies
• Twin anaemia polycythaemia sequence is similar to twin-twin transfusion syndrome, but less acute. One twin becomes anaemic whilst the other develops polycythaemia (raised haemoglobin).
• Women with multiple pregnancies require additional monitoring for anaemia, with a full blood count at:

  • Booking clinic
  • 20 weeks gestation
  • 28 weeks gestation
• Additional ultrasound scans are required in multiple pregnancy to monitor for fetal growth restriction, unequal growth and twin-twin transfusion syndrome:

  • 2 weekly scans from 16 weeks for monochorionic twins
  • 4 weekly scans from 20 weeks for dichorionic twins
• Planned birth is offered between:

  • 32 and 33 + 6 weeks for uncomplicated monochorionic monoamniotic twins
  • 36 and 36 + 6 weeks for uncomplicated monochorionic diamniotic twins
  • 37 and 37 + 6 weeks for uncomplicated dichorionic diamniotic twins
  • Before 35 + 6 weeks for triplets
• Corticosteroids are given before delivery to help mature the lungs.
• Monoamniotic twins require elective caesarean section at between 32 and 33 + 6 weeks.

  Diamniotic twins (aim to deliver between 37 and 37 + 6 weeks):

  • Vaginal delivery is possible when the first baby has a cephalic presentation (head first)
  • Caesarean section may be required for the second baby after successful birth of the first baby
  • Elective caesarean is advised when the presenting twin is not cephalic presentation