Multiple Pregnancy Flashcards
What is meant by multiple pregnancy?
a pregnancy with more than one foetus
What is the main factor in determing pregnancy outcome?
How is this identified?
- chorionicity is the main factor influencing pregnancy outcome
- this can be identified on US at 10-14 weeks
chorionicity = the number of placentas
What is the difference between a monozygotic and dizygotic pregnancy?
monozygotic:
- identical twins that have come from the same zygote
dizygotic:
- non-identical twins that have come from 2 different zygotes
dizygotic - 2 eggs are fertilised by 2 different sperm
monozygotic - the fertilised ovum splits to develop into 2 embryos
What is the difference between monoamniotic and diamniotic?
monoamniotic:
- there is a single amniotic sac
diamniotic:
- there are 2 separate amniotic sacs
What is the difference between monochorionic and dichorionic?
monochorionic:
- there is a single placenta
dichorionic:
- there are 2 separate placentas
What type of twin pregnancy has the best outcome?
diamniotic dichorionic
- this is because each fetus has their own nutrient supply
What type of pregnancy is dizygotic pregnancy associated with?
- this involves the fertilisation of 2 separate oocytes with 2 different sperm
- this produces a diamniotic dichorionic pregnancy
In a monozygotic pregnancy, how may a diamniotic dichorionic pregnancy result?
- this occurs if the zygote divides within the first 3 days of conception
- this results in each fetus having its own placenta and own amniotic cavity
What is the most common outcome of monozygotic pregnancies?
How does this occur?
monochorionic diamniotic
- this accounts for 70% of monozygotic pregnancies
- there is sharing of a placenta, but each twin has its own amniotic sac
- this occurs when the blastocyst divides between day 4 to 7 after conception
What are the other potential outcomes of monozygotic pregnancy and why do they occur?
monochorionic monoamniotic:
- occurs when the implanted blastocyst divides between day 8 and 13
conjoined twins:
- occurs when there is division of the formed embryonic disc after 13 days
- in both these cases there is sharing of the placenta and amniotic sac
How is multiple pregnancy diagnosed?
- on the booking ultrasound scan
- US can also be used to identify the chorionicity (number of placentas) and amnionicity (number of amniotic sacs)
What US sign is associated with dichorionic diamniotic twins?
lambda / twin peak sign
- this occurs as there is a membrane between the twins
- separation of the chorionic + amniotic sacs resembles a lambda
What US sign is associated with monochorionic diamniotic twins?
T sign
- there is a membrane between the twins
- the T represents separation of the amniotic sacs
What are the potential risks to the mother associated with multiple pregnancy?
- anaemia
- polyhydraminos
- hypertension / pre-eclampsia
- malpresentation
- spontaneous preterm birth
- instrumental delivery / CS
- antepartum / postpartum haemorrhage
What are the major risks to foetuses associated with multiple pregnancy?
- miscarriage / stillbirth
- fetal growth restriction
- congenital abnormalities
- twin-twin transfusion syndrome
- twin anaemia polycythaemia sequence
structural abnormalities are 2-3x higher in monozygotic twins
What must the circumstances be for twin-twin transfusion syndrome to occur?
it only occurs in monochorionic pregnancies in which the twins share the placenta
What happens in twin-twin transfusion syndrome?
- there is a connection between the blood supplies of the 2 fetuses
- one fetus receives the majority of the blood from the placenta and is the “recipient”
- the other fetus is starved of blood and is the “donor”
What are the consequences for the donor and recipient twin in TTTS?
donor twin:
- growth restriction
- anaemia
- oligohydraminos
recipient twin:
- polyhydraminos
- cardiac failure
What is the management for TTTS?
laser ablation
- this may be used in severe cases to destroy the connection between the 2 blood supplies
What is twin anaemia polycythaemia syndrome?
- it is similar to TTTS, but less acute
- one twin develops anaemia
- the other develops polycythaemia (raised Hb)
What additional blood tests are required in multiple pregnancy?
- additional monitoring for anaemia is required
- FBC is performed at booking clinic
- and at 20 weeks and 28 weeks gestation
What additional US scans are needed in multiple pregnancy?
monochorionic twins:
- US scans every 2 weeks from 16 weeks gestation
dichorionic twins:
- US scans every 4 weeks from 20 weeks gestation
Why are additional US scans required in multiple pregnancy?
to assess for evidence of:
- fetal growth restriction
- unequal growth
- twin-twin transfusion syndrome
What other additional tests are offered to women with multiple pregnancy?
regular BP measurements and urine dips to check for pre-eclampsia
What additional medication is offered in multiple pregnancy?
- folic acid 5mg to reduce the risk of congenital abnormalities
- aspirin 75mg as prophylaxis against pre-eclampsia
- oral iron to prevent anaemia
When is planned birth offered for DCDA twins?
between 37 and 37+6 weeks gestation
When is planned birth offered for MCDA twins?
between 36 and 36+6 weeks gestation
When is planned birth offered for MCMA twins?
between 32 and 33+6 weeks gestation by planned caesarean-section
What are the delivery options for multiple pregnancies?
- if the presenting twin is cephalic, vaginal delivery is recommended
- if the presenting twin is breech / transverse lie, C-section is performed
Why is planned delivery performed in multiple pregnancy?
What additional medication may be required?
- waiting beyond the recommended dates is associated with increased risk of fetal death
- corticosteroids are given prior to delivery to mature the fetal lungs
