3. Incidence of Twins
• Monozygotic
• Fairly constant at 4 per 1000
• Dizygotic
• About 8 per 1000 in the United States
• Varies according to:
• Country (45 per 1000 in Nigeria)
• Maternal age (14 per 1000 at ages 35-40)
• Race
• Genetic predisposition
• Assisted reproduction
4. Types of twin pregnancy
• Dizygotic and monozygotic.
• Dizygotic twins occur when two ova are fertilized and have separate
amnions, chorions, and placentas (dichorionic diamniotic).
• The placentas may fuse if the implantation sites are close together.
• The majority of twin pregnancies are dizygotic
• Monozygotic twins develop when a single fertilized ovum or zygote
divides after conception
5. Placentation
• Monozygotic Timing of Egg Cleavage
• Dichorionic/Diamniotic (fused or
separate placenta) Day 0-3
• Monochorionic/Diamniotic Day 4-8
• Monochorionic/Monoamniotic Day 8-
13
• Conjoined Beyond Day 13
• Dizygotic
• Dichorionic/Diamniotic (fused or
separate placenta)
70%
30%
≤1%
6. Determination of amnionicity and chorionicity
• Ultrasound determination of amnionicity and chorionicity is best
achieved in the first trimester by examining the inter-twin membrane
at its placental attachment and identifying the lambda (λ) or T sign.
• The earliest gestation for determining chorionicity is 5 weeks
• Amnionicity determined earliest at 8 weeks.
• The lambda sign or the ‘twin peak’ sign is seen in dichorionic twin
pregnancy.
• Appears as a triangular tissue projection extending from the base of
the inter-twin membrane, giving the characteristic appearance of the
Greek letter lambda (λ).
7. • Determine chorionicity and amnionicity early - first trimester
• Studies suggest a sensitivity and a specificity of 97–100% for accurate
determination of dichorionicity using the lambda sign.
• Studies suggest a sensitivity and a specificity of 98–100% for accurate
determination of monochorionicity using the T-sign.
• In MCDA both amnions meet perpendicularly on the placenta surface.
12. Monochorionic Twins
• Interfetal blood vessel communications nearly always present
• Artery-to-artery (75% of MC placentas)
• Vein-to-vein (50% of MC placentas)
• Artery-to-vein (5-17% of MC placentas)TTTS
13. TWIN TO TWIN TRANSFUSION SYNDROME
• TTTS is the most important cause of death and handicap in
monochorionic twin pregnancies.
• Thought to arise from an inter-twin transfusion imbalance across the
vascular anastomoses.
• Results in hypervolaemia, polyuria, and polyhydramnios in the
recipient and hypovolaemia, oliguria, and oligo-anhydramnios in the
donor.
16. TTTS
• occurs in 15% of monochorionic twin pregnancies which overall is
about 1 in 2000 pregnancies.
• It typically manifests around 16–26 weeks.
• The presentation of TTTS is variable and its course can be
unpredictable.
• May present as a slow onset disease or be rapidly progressive.
• If untreated, the condition is associated with an 80% rate of perinatal
mortality and a 15–20% risk of brain injury in survivors.
• Diagnosis of TTTS is based on ultrasound criteria of amniotic fluid
discordance
17. • Classification of TTTS currently based on amniotic fluid discordance
• Currently classification and staging based on the Quintero system
18. Quintero Staging
• Stage I: Amniotic fluid discordance- Oligo and Poly, but the
donor twin bladder is visible
• Stage II: The bladder of the donor twin is no longer visible
• Stage III: Abnormal Doppler studies are evident (usually in
donor twin)
• Stage IV: Hydrops
• Stage V: One or both fetuses have died
19. Screening for TTTS in monochorionic twin
pregnancies
• Should commence from 16 weeks’ gestation onwards.
• Fortnightly assessment of growth, deepest vertical pool of amniotic
fluid, and umbilical artery Doppler is recommended.
• Care should be taken to note a free-floating inter-twin membrane and
fetal bladder in both twins.
• Where there is discrepancy in amniotic fluid or folding of the
intertwin membrane, increased surveillance (usually weekly) should
be offered to exclude progression to TTTS
20. TTTS - MANAGEMENT
• Serial Reduction Amniocentesis
• Amniotic septostomy
• Laser Ablation of the anastomoses (A-V anastomoses)
• Gold standard
21. • The gold standard treatment for TTTS diagnosed before 26 weeks >
laser ablation.
• Evidence suggests that it leads to better outcomes compared with
amnioreduction or septostomy
22. Serial Amnioreduction
• AF removed under US guidance from polyhydramnios sac w/18gauge
spinal needle
• DVP <5cm
• Repeated prn
• MOA for fluid balance: unknown
• Theory: removal of fluid from the recipient allow for better perfusion
of the donor’s placenta thus restoring the fluid of the donor’s sac
• Perinatal survival rates 60-65%
• Cerebral palsy rate 4.7% - 26%
23. Amniotic Septostomy
• 20 gauge spinal needle inserted through the dividing membrane under u/s
guidance
• Amniotic fluid equilibrates across the disrupted membrane
• MOA: unknown
• Theory: similar to serial AF reduction, also may allow donor to swallow more
fluid to augment it’s circulating volume
• May prolong pregnancy by 8 wks, 65% survival
• Survival no different from serial AF reductions
• CAUTION: may cause monoamniotic gestation
25. Laser Ablation
• De Lia, et al developed the technique in 1990
• Goal: coagulation of all superficial placental vessels shared (A-V) by
fetoscopically directed neodymium-YAG laser
• Technique is a major advantage over the other techniques
• Survival rates 64%- 88%
26. • Neurologic handicap after 12mos of follow-up- 4% (less than the AF
reduction group)
• 78% normal development at a median age of 22 months
• Fetoscopic laser technique is offered for stage II to stage IV TTTS.
• Recurrence for TTTS after laser ablation is about 14%.
• Another option for severe TTTS is selective termination of pregnancy
using bipolar diathermy, laser coagulation, or radiofrequency ablation
of one of the umbilical cords
• Termination of the entire pregnancy is also an option for severe TTTS
27. Complications
• Without treatment, the perinatal mortality rate is 70-100%
• After laser therapy, there is a 85% chance of having one living fetus and 60-70% chance of taking
home two live infants.
• Procedure related complications
• PPROM 25%
• TAPS 16%
• Abruption 8%
• Vascular laceration 3%
• Neonate
• Periventricular leukomalacia ~10% > Cerebral palsy, hydrocephalus,seizure disorders
• Intraventricular hemorrhage ~10%
• Risk for long term neurological handicaps 5-20%
28. TWIN ANAEMIA – POLYCYTHEMIA SEQUENCE
(TAPS)
• TAPS results from slow blood transfusion from donor to recipient
• Occurs through a few minuscule vascular anastomosis
• Gradually leads to anaemia in the donor and polycythemia in the
recipient
• TAPS may occur spontaneously in 3-5% of monochorionic twins and
also after laser surgery for TTTS (2%-16%)
30. TAPS - DIAGNOSIS
• Prenatal diagnosis of TAPS – based on discordant measurements of
the middle cerebral artery peak systolic velocity
• The prenatal diagnosis of TAPS is based on the finding of a discordant
middle cerebral artery (MCA) Doppler—MCA peak systolic velocity
(PSV) > 1.5 multiples of the median (MoM) in the donor, suggesting
fetal anaemia, and MCA PSV < 1.0 MoM in the recipient, suggesting
polycythemia.
• In pregnancies complicated by TAPS, the risk of neurodevelopmental
delay is around 20%.
31. TAPS - MANAGEMENT
• The management options depend on the gestational age at diagnosis,
parental choice, severity of the disease, and technical feasibility of
intrauterine therapy:
• conservative management
• early delivery
• laser ablation, or intrauterine blood transfusion for the anaemic twin,
combined intrauterine blood transfusion for the anaemic twin, and
partial exchange transfusion to dilute the blood of the polycythaemic
twin.
32. SELECTIVE FETAL GROWTH
RESTRICTION(sIUGR/sFGR)
• Applicable to cases in monochorionic pregnancies where the EFW of
the small fetus falls below the tenth percentile and the inter-twin
growth discordance is greater than 25%.
• sFGR present in about 10–15% of all monochorionic twin pregnancies
and in a small proportion can coexist with a superimposed TTTS.
• Pathophysiology > inadequate placental sharing, possibly in
association with very eccentric or velamentous cord insertion, and
the presence of vascular anastomoses in the monochorionic placenta.
33. Subtypes of sIUGR/sFGR
• 3 subtypes depending on whether there are umbilical artery Doppler
abnormalities
• Type I sIUGR - The lowest risk type, there is positive end-diastolic flow
in the UAD of the growth-restricted fetus,
- If this persists, the outcome can be good with over 90% survival.
• Type II - Persistent absent or reversed end-diastolic flow in the UAD of
the growth-restricted fetus,
- there is a risk of fetal death of either twin in up to 29% and
neurological sequelae in 15% of cases born before 30 weeks.
34. Subtypes of sIUGR/sFGR
• Type III sFGR - there is a cyclical pattern present—absent and
reversed end-diastolic flow in the umbilical artery waveform of the
growth restricted fetus.
• Associated with 10–20% risk of sudden death of the growth restricted
fetus, and a high rate of neurological morbidity (up to 20%) in the
larger twin.
35. sIUGR/sFGR – Management options
• Conservative management followed by early delivery.
• fetoscopic laser ablation, or cord occlusion of the growth-restricted
twin (in order to protect the co-twin).
• Irrespective of the presence or absence of intervention, such
pregnancies are at a high risk of iatrogenic preterm delivery.
36. TWIN REVERSED ARTERIAL PERFUSION
SEQUENCE(TRAP)
• Rare complication of monochorionic twin pregnancies
• Characterized by the presence of a TRAP or acardiac mass perfused by an
apparently normal (pump) twin.
• The perfusion occurs in a retrograde fashion through artery–artery
anastomoses, usually through a common cord insertion site.
• This may lead to a hyperdynamic circulation and progressive high-output
cardiac failure in the pump twin.
• The risk of demise of the pump fetus in TRAP sequence managed
conservatively is up to 30% by 18 weeks’ gestation.
• Invasive techniques to treat TRAP sequence that have been described
include cord occlusion using bipolar diathermy, intrafetal laser ablation or
radiointerstitial thermal ablation.
38. Co-twin demise in twin gestation
• Single twin demise after 14 weeks – occurs between 2.6% and 6.2%
of all twin pregnancies.
• Spontaneous death of one fetus occurs in 1% of monochorionic twins.
• Associated with acute haemorrhage from the co-twin into the
fetoplacental unit of the dead one
• In the co-twin - 15% risk of death and at least 25% of survivors have
severe neurologic injury
• Also high risk (60-70%) of preterm birth
39. • If death of 1 twin occurs < 24 weeks gestation, co-twin likely to die
• If co-twin survives neurologic injury is likely to be less
• If death occurs > 24 weeks, co-twin is more likely to survive but more
likely to suffer brain damage
40. • Following death of 1 twin the ff complications may occur in
monochorionic and dichorionic pregnancies repectively:
- death of the co-twin (15% and 3%)
- preterm delivery (68% and 54%)
- abnormal postnatal cranial imaging of the surviving co-twin (34% and
16%)
- neurodevelopmental impairment of the surviving twin (15–26% and
2%)
41. Co-twin demise – management and
challenges
• The optimal time of delivery
• The frequency of antenatal surveillance
• Appropriate investigations to determine cerebral damage and
neurological morbidity
• Effects on maternal well-being (both physical and psychological) of
retaining one dead fetus.
• co-twin demise in monochorionic twins >
- risk of acute TTTS, and resultant anaemia in the surviving fetus and
risk of brain injury
42. Co-twin demise - Recommendations
• Follow-up the pregnancy with serial MCA PSV measurements to check
for fetal anaemia
• Blood transfusions if MCA Doppler suggestive of fetal anaemia
• Fetal MRI of the brain 4–6 weeks after the event.
• Such pregnancies should be managed in a tertiary fetal medicine unit
• Surviving child would need neurodevelopmental assessment up to
2 years of age
43. When to Deliver multiple pregnancies
• Di/Di Concordant, Uncomplicated
• 37-38 weeks
• Mo/Di Concordant, Uncomplicated
• 34-37 weeks*
• Mo/Mo Concordant, Uncomplicated
• 32-34 weeks(. Most MCMA twins have cord entanglement and are best delivered by
caesarean section, after corticosteroids.)
• Tri/Tri Concordant
• 35-36 weeks
• Monochorionic pair (as above if earlier)
• Quads
• 32 weeks
44. Factors Affecting Mode of Delivery in Twins
• Gestational Age
• Estimated Fetal Weight
• Growth Discordance
• Indication for Delivery
• Medical/Obstetric Factors
• Fetal Presentation
• Provider Skills/Hospital Resources
46. Intrapartum Management - Twins
• Vertex/Vertex
• Cesarean section should be performed for the same indications
applied to singletons
• Vertex/Non-vertex
• Management is controversial
• Non-vertex presenting twin
• Cesarean section is the method of choice
47. Vertex-Nonvertex Twins Delivery
• Cesarean section
• Recommended in absence of skilled obstetrician or if significant growth
discordance
• External cephalic version of 2nd twin
• Success rates reported between 46-72%
• Breech extraction of 2nd twin
• Retrospective studies differ from large epidemiologic studies
• Reasonable if:
• EFW is >1500 gms and <3500 gm
• <20% growth discordance
• Should be performed as soon as possible after delivery of first twin
• Anesthesia and OR available, CEFM, ultrasound
49. • Oxford Textbook of obstetrics and gynaecology. Chapter 20, Multiple
pregnancies
• Lisanne S.A. Tollenaar et al. Twin anaemia-polycythaemia sequence:
Current views on pathogenesis, diagnostic criteria, perinatal
management and out comes. Twin ResHum Genet June 2016
• Lecture by Dr D’Angela Pitts . Queenan fellow in MFM
• Fetal Medicine Foundation: Multiple pregnancies. MC twins: Death of
one fetus
Editor's Notes
Performed for Stage II and above.
GA 16 weeks- 26 weeks
Risk of stillbirth in twins at 37-38 weeks approaches that of post-term singleton
*Risk of unexpected fetal death in MC pregnancies 3-4% after 24 weeks, usually at 34 weeks. Some advocate delivery as early as 34-35 weeks after BMZ vs 36-37 weeks (Cleary-Goldman, D’Alton. PLoS Med. 2005; 2: e180).
**Data is very limited on higher-order multiples; most of these pregnancies will either spontaneously deliver 28-32 weeks or have indicated PTD
