Twin Pregnancies

Question 1

Definition of monozygous

Answer 1

Twins arising from a single fertilised egg that has divided into two growing embryos

Question 2

Definition of dizygous

Answer 2

Twins arising from two separate fertilised eggs

Question 3

Definition of chorionicity

Answer 3

Refers to the number of outer membranes surrounding the foetus and the corresponding placentation

Question 4

Definition of amnionicity

Answer 4

Refers to the inner membrane layers that do or do not separate the gestational sacs of twins

Question 5

Prevalence of twins in Australia

Answer 5

1-2% of pregnancies

Question 6

Statistics of dizygotic v monozygotic v conjoined twins

Answer 6

70% of twins dizygotic
30% of twins monozygotic
- 1 in 200 of these will be conjoined

Question 7

Definition of monochorionic monoamniotic

Answer 7

(MC/MA) no membranes separating the twins - they share a gestational sac

Question 8

Definition of monochorionic diamniotic

Answer 8

(MC/DA) the membrane separating the twins is only two layers consisting of amnion, placenta is shared

Question 9

Definition of dichorionic diamniotic

Answer 9

(DC/DA) membrane separating twins consists of layers of both amnion and chorion, they have separate placentae which may or may not fuse

Question 10

Complications of twin pregnancy

Answer 10

Higher frequency and severity of pregnancy symptoms (hyperemesis, respiratory discomfort)
Preterm birth (less than 50% continue to 38 weeks)
IUGR
Increased incidence of complications (miscarriage, anaemia, polyhydramnios, PET, GDM, congenital anomalies, malpresentations, cord accidents, PPH)
TTTS - in monochorionic twins
Antepartum death of one twin
Increased risk of long term infant adverse outcomes e.g. CP

Question 11

Complications specific to monochorionic twins

Answer 11

Twin to twin transfusion syndrome (twin oligohydramnios/polyjhydramnios sequence or twin anaemia/polycythaemia sequence)
Death of one twin
SPECIFIC TO MONOAMNIOTIC:
Cord entaglement in utero
Twin reversed arterial perfusion sequence

Question 12

Complications specific to monoamniotic twins

Answer 12

Cord entanglement in utero

Twin reversed arterial perfusion sequence

Question 13

Prevalence of twin to twin transfusion syndrome

Answer 13

develops in 15% of monochorionic twins (accounts for 15% perinatal mortality)

Question 14

Clinical features of TOPS (classical) type of TTTS

Answer 14

Oligohydramnios, poor growth and abnormal umbilical artery Doppler in donor
Polyhydramnios progressing to cardiac dysfunction and failure in the recipient

Question 15

Clinical features of TAPS type of TTTS

Answer 15

Slightly discordant middle cerebral artery peak systolic velocities (reflects anaemia and polycythaemia in donor and recipient respectively)
More common in later pregnancy
Can be associated with significant foetal anaemia and in utero compromise

Question 16

Common cause of TAPS type of TTTS

Answer 16

Secondary to undergoing laser treatment for TOPS

Very slow transfusion from donor to recipient (thus fluid remains constant, but Hb slowly increases)

Question 17

Surveillance of twins with TTTS

Answer 17

USS examination for:

• growth
• amniotic fluid volume in each sac
• bladder volume
• umbilical artery Doppler wave forms (after 24 weeks)
• MCA Doppler wave forms after 24 weeks

Question 18

When is clinical suspicion of TTTS raised

Answer 18

Early discordance in foetal size or nuchal translucency

Discordance in foetal growth/size (+/- poly/oligo-hydramnios)

Rapid increase in maternal abdominal girth (rapid accumulation of polyhydramnios)

Question 19

Treatment of TTTS

Answer 19

Serial amnioreduction via amniocentesis
OR
Fetoscopic laser ablation of placental vascular anastamoses in second trimester (higher survival rate and lower neurological morbidity postnatally than amniocentesis)

Question 20

Additional monitoring of monoamniotic twins

Answer 20

Frequent CTG once reach viability

Delivery is indicated if cord compression is diagnosed

Question 21

Changes in antenatal care in twin pregnancy v singleton

Answer 21

More frequent antenatal visits
Iron and folic acid supplements in all mothers (regardless of iron stores)
Second trimester screening for T21 is not applicable - NT is main test
USS every 3-4 weeks from 24w onwards

Question 22

Screening and diagnosis of Down syndrome in twin pregnancies

Answer 22

Nuchal translucency is most useful parameter (thus second trimester screening basically useless)

Question 23

Delivery of twin pregnancy

Answer 23

Must be at a higher level hospital (at least level 4)
Monochorionic from 36 weeks on
Dichorionic from 37 weeks on
Vaginal birth if meets conditions
C-section at 38 weeks if does not
Monoamniotic twins: c-section at 32 weeks

Question 24

Conditions for vaginal delivery of twins

Answer 24

• Twins are diamniotic
• Twin 1 is cephalic
• Twin II is not more than 500g heavier than twin I
• Neither twin has evidence of foetal compromise