Multiple pregnancy Flashcards
How common are multiple pregnancies?
- twins: 1/105 (although now around 3%)
- triplets: 1/10,000
97-99% of multiple pregnancies are twins
What is a key risk factor for multiple pregnancy?
Maternal age >45years –> 1 in 10 are multiple pregnancies
IVF –> 1 in 5 successful pregnancies are multiple. NB: around a third of twin pregnancies and 80% of triplet pregnancies occur after IVF.
What are the two types of twins?
Dizygotic - non-identical, develop from two separate ova that were fertilized at the same time
Monozygotic - identical, develop from a single ovum which has divided to form two embryos
What are the different chorionicities and amnionicities in multiple pregnancy? What are the sexes?
Dizygotic
- Dichorionic diamniotic (DCDA)
- Same sex or different sex
Monozygotic
- Dichorionic
- DCDA
- Same sex only
- Monochorionic
- MCDA - same sex only
- MCMA - non-conjoined, conjoined

What is zygocity?
Number of fertilised eggs
What are DCDA twins separated by? What about MCDA?
DCDA - fused amnion in the middle with chorion on either side
MCDA - single layer of amnion alone

Is monozygotic or dizygotic more common? Why?
Around 70-80% of twins are dizygotic
Rate of monozygotic twins has remained constant but incidence of dizygotic twns is increasing due to infertility treatments

At which scan is multiple pregnancy detected?
10-13+6 week dating scan, excludes multiple pregnancy (chorionicity is also confirmed: ‘twin peak’ or ‘lambda’ sign is seen in dichorionic cases)
Monochorionic and dichorionic twin pregnancies shown below.

Is SFH measurement useful in multiple pregnancy?
No and should not be used to predict FGR
What are the complications associated with monoamniotic monozygotic twin pregnancies?
- increased spontaneous miscarriage, perinatal mortality rate (x5)
- increased malformations, IUGR,
- prematurity - 12% born before viability and 25% born between 24-32 weeks
- monochorionic diamniotic
- twin-to-twin transfusions (TTTS): recipient is larger with polyhydramnios (do laser ablation of interconnecting vessels)
- twin anaemia-polycythaemia sequence (TAPS)
What are the predisposing factors for a dizygotic twin pregnancy?
- previous twins
- family history
- increasing maternal age
- multigravida
- induced ovulation and in-vitro fertilisation
- race e.g. Afro-Caribbean
What are the maternal complications of multiple pregnancy?
- pregnancy induced hypertension
- thromboembolic disease
- anaemia - higher risk than singleton pregnancy so should be checked at 20 and 28 weeks and supplementation with Fe, folic acid or B12 initiated.
- antepartum haemorrhage
What are the fetal complications of multiple pregnancy?
- prematurity
- fetal growth restriction
- cerebral palsy
- stillbirth
- malformation (*3, especially monozygotic)
At what gestation are most twins and triplets delivered?
Mean:
- Twins = 37 weeks,
- Triplets = 33 weeks
What are the intrapartum complications of multiple pregnancy?
- PPH increased (*2)
- malpresentation
- cord prolapse, entanglement
When is the death of one twin particularly complicated in a twin pregnancy?
In monochorionic twins - the survivor twin can have immediate complications e.g. death, brain damage, neurodevelopmental issues.
In dichorionic twins, pregnancy can sometimes continue uneventfully after the death of one twin and can even result in delivery at term.
Name 2 complications which are unique to monohorionic twin pregnancies.
Twin to twin transfusion syndrome (TTTS)
Twin anaemia-polycythaemia sequence (TAPS)
What is the cause of TTTS? What 4 types of vascular connections may be found in monochorionic pregnancies?
Abnormal unbalanced vascular anastomoses in a monochorionic pregnancy.
Four different vascular connections may be found:
- arteriovenous (AV)
- arterioarterial (AA)
- venoarterial (VA)
- venovenous (VV)
What is the pathophysiology of TTTS?
- Vascular connections are unbalanced
- More AV connections occurring in one direction than the other
- Alterations in hydrostatic and osmotic forces occurs
- This causes TTTS manifestations
If the bidirectional anastomoses were of equal number then balanced connections would be found and TTTS would not occur
Which anastomoses are protective against TTTS in monochorionic pregnancy?
AA - arterioarterial
What is the diagnostic criteria for TTTS?
Based on US findings:
- Single placental mass
- Concordant gender
- Oligohydramnios with maximum vertical pool (MVP) <2cm in one sac and polyhydramnios in the other (MVP >8cm)
- Discordant bladder appearances
- Haemodynamic and cardiac compromise
What staging is used for the severity of TTTS?
Quintero staging
What are the Quintero stages for severity of TTTS?
Stage I: Oligohydramnios + polyhydramnios sequence + bladder of donor twin visible. Dopplers normal.
Stage II: Oligohydramnios +polyhydramnios sequence, but bladder of donor twin not visualized. Dopplers normal.
Stage III: Oligohydramnios + polyhydramnios sequence, non-visualized bladder and abnormal Dopplers. There is absent/reversed end-diastolic velocity in the umbilical artery, reversed flow in a-wave of the DV or pulsatile flow in the umbilical vein in either fetus.
Stage IV: One or both fetuses show signs of hydrops.
Stage V: One or both fetuses have died.

Define TAPS.
Rarer chronic form of TTTS in which a large inter-twin haemoglobin difference occurs but the oligohydramnios polyhydramnios sequence that is observed with TTTS is not seen.
