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.
What is the pathophysiology of TAPS?
- Thought to be due to residual small (<1 mm) unidirectional AV anastomoses without accompanying AA anastomoses.
- The small residual anastomoses lead to the gradual development of anaemia in one twin and polycythaemia in the other twin. As the vessels are small, this allows haemodynamic compensation, which is thought to be why the characteristic oligohydramnios polyhydramnios pattern does not occur.
- Severe polycythaemia can occur, leading to fetal and placental thrombosis and hydrops fetalis in the anaemic twin.
- Rarely, mirror syndrome, the combination of fetal hydrops and maternal pre-eclampsia, has been reported,
How often are monochorionic pregnancies monitored for TTTS?
Generally fortnightly USS from 16 weeks to 24 weeks
What is the management of TTTS?
Refer to specialist centre
Options include:
- Expectant management
- Amnioreduction
- Septostomy
- Selective feticide
- Fetoscopic laser ablation of vascular anastomosis -definitive treatment for severe (Quintero stage II or >) TTTS between 16-26 weeks
- Delivery - consider above 26 weeks
What does fetoscopic laser ablation involve?
- Performed under local, regional or general anaesthetic
- 2-3mm diameter fetoscope is inserted into the amniotic cavity of the recipient twin
- Location of dividing twin membrane between amniotic cavities is found
- AV anastomoses are ablated using laser energy
- Fetoscope is removes
- Amniodreduction is performed until amniotic fluid volume appears normal on USS
What is the antenatal management of multiple pregnancy?
Antenatal (NICE):
-
Appointments:
- Uncomplicated DC= 8 appointments
- Uncomplicated MCDA = 9 appointments
- If triplets etc = 11 appointments
- Routine screening for HTN and GDM (higher risk in twin)
- Routine (not selective) supplementation of iron and folic acid is recommended
-
Ultrasound scans, note:
- DC twins - Down’s risk is calculated for each baby
- MC twins - Down’s risk calculated for pregnancy as a whole
- Higher rates of congenital anomalies in twins
- Check signs of TTTS, aneuploidy, fetal abnormalities
- Risk of IUGR higher - growth scans should be done no less than every 4 weeks
What is the intrapartum management of multiple pregnancy?
Intrapartum:
- Precautions at labour (e.g. 2 obstetricians present, 2 paediatricians, 2 neonatal resuscitation trolleys), analgesia (to allow for internal podalic version for twin 2 if necessary), oxytocin for PPH, portable US.
- Coninuous CTG monitoring
- Vaginal delivery advocated provided first twin is cephalic
In DC twins, delivery from 37 weeks is advocated. MC twins should be delivered by C-section from 36 weeks (once steroids given). MCMA twins should be delivered at 32-34 weeks by C-section. If triplets, deliver by 36 weeks. Multiple pregnancies continuing >38 weeks increases risk of IUD.
* (MCMA twins are closely monitored and sometimes hospitalised from week 28 and delivered by C/S at 32-34 weeks)
In a vaginal twin delivery, what happens when the second twin is breech?
- ECV (70% success rate)
- If ECV fails, internal podalic version
What is internal podalic version?
Fetal foot identified through intact membranes
Foot is grasped and pulled gently into birth canal
Membranes are ruptured as late as possible
Why should MCMA twins be delivered by C-section?
Risk of cord entanglement and death is high
Normally done at 32-34 weeks with corticosteroids administered 7 days before delivery
Which of the following pregnancy complications does NOT increase in incidence in multiple pregnancy?
- A Pre-eclampsia.
- B Obstetric cholestasis.
- C Preterm delivery.
- D Macrosomia.
- E FGR.
D
Which of the following is NOT a Quintero stage for TTTS?
- A Oligohydramnios and polyhydramnios sequence and the bladder of the donor twin is visible. Dopplers in both twins are normal.
- B Growth restriction in both twins, raised middle cerebral artery Dopplers and reduced fetal movements in both twins.
- C Oligohydramnios and polyhydramnios sequence, non-visualized bladder and abnormal Dopplers. There is absent/reversed enddiastolic velocity in the umbilical artery, reversed flow in a-wave of the DV or pulsatile flow in the umbilical vein in either fetus.
- D One or both fetuses have died.
- E One or both fetuses show signs of hydrops.
B
