TWINS

Question 1

What is zygosity?

Answer 1

The number of zygotes contributing to a multiple pregnancy ie, monozygotic = originates from single zygote (one fertilised ovum).

Question 2

What is chronicity?

Answer 2

The number of placentas in a monozygotic pregnancy. Determined by timing of zygote cleavage
1-4 days:  dichorionic diamniotic 
4-8 days:  monochorionic diamniotic
8-12 days:  monochorionic monoamniotic
13+ days: conjoined

Question 3

How do you determine chorionicity in a twin pregnancy?

Answer 3

Early pregnancy ( ie < 14 weeks) USS to access placental masses + amnion

• Lambda sign or twin peak sign: dichorionic ( thick membrane)
• T sign: monochorionic (thin membrane)

(placentas fuse at later gestation)

> 20 weeks

• gender discordance
• visualisation of intertwine membrane
• layers of inter-twin membrane
• thickness of membrane ( in DC)

Question 4

How do you determine the age of a twin pregnancy?

Answer 4

First tri USS, estimate GA from largest fetes

Question 5

How many ANC visits should DCDA twins have (uncomplicated) ?

Answer 5

11-14 weeks, 20 weeks, 24 weeks, 28 weeks, 32 weeks, 36 weeks with USS

Question 6

How many ANC visits should monochorionic twins have?

Answer 6

11-14 weeks, then 2 weekly until 34

Question 7

What is TTTS?

Answer 7

Complication of monochorionic twins caused by uneven distribution of vascular anastomoses
a) TOPS ( twin oligo/poly sequence) midtrimester,
donor twin is hypovolaemic,
–> RAS activated to increase intravascular volume
–> oligo

Recipient twin is hypervolaemic

• -> BNP and ANP activated to reduce volume–> polyuria–>polyhydramnios
• -> ventricular hypertrophy–> venous HTN–>lymphatic obstruction–> hydrops

Quintero stages ( PADHI 1-5)

TAPS ( twin anaemia/polythaemia sequence)

Question 8

Whats the management of TTTS?

Answer 8

Conservative ( mortality ~ 90%)

Medical

• maternal dig ( improves cardiac function in recipient twin)
• indomethacin ( improves polyhydramnios in recipient twin by reducing renal percussion, reduced PPROM/PTB, worsens oligo)

Interventional
- TOP ( early severe TTTS)

• Selective termination of one fetus by cord ligation (life threatening anomaly after failed laser ablation)
• fetoscopic laser ablation ( selective occlusion of selected anastomotic vessels Definitive rx 16-26/40
• septostomy. Hole in membrane to equilibrate AFI. Mostly abandoned
• Delivery if viable

Question 9

How common are monozygotic twins?

Answer 9

3-5:1000 births

Question 10

When should you deliver twins?

Answer 10

Uncomplicated DCDA: 38/40
Uncomplicated MCDA: 36-37/40
Uncomplicated MCMA: consultant dependent

Question 11

When is vaginal delivery for twins ok?

Answer 11

• Cephalic presenting twin.
• Non presenting twin EFW not > 20% bigger
• GA < 28/40 or second twin < 1500g
• Delivery of first twin suggests delivery of second twin will be ok

Landmark trial ( Barrett 2013)

• RCT, 2800 women, 37+5= 38+6 , first twin cephalic
• planned CS or NVB
• 90% of planned CS actually had CS, 44% planned NVB actually had NVB
• el. CS delivered earlier
• no difference in neonatal composite outcome ( fetal or neonatal death), serious neonatal morbidity, ?maternal morbidity
• NO DIFFERENCE IN OUTCOME IF FIRST TWIN CEPHALIC

Question 12

How common are twins?

Answer 12

1:80

Question 13

What are the specific complications of MCDA twin pregnancies?

Answer 13

• TTTS
• TRAP sequence
• Selective IUGR
• Single twin FDIU
• Congenital anomalies x 3 higher ( esp. cardiac)
• increased stillbirth
• 60% chance delivery < 37/40