2. DATING OF TWIN PREGNANCY
• CRL OF 45 – 84 mm
• In pregnancies conceived spontaneously, the larger of the 2 CRL should be used
to estimate gestational age
• After 14 weeks, the larger head circumference should be used
• In-vitro fertilization should be dated using the oocyte retrieval date of the embryonic
age from fertilization
3. DETERMINING CHORIONICITY / AMNIONICITY
• Chrorionicity should be determined 11 to 13 weeks 6 days of gestation using the
membrane thickness at the site of insertion of the amniotic membrane into the
placenta
4.
5. DETERMINING CHORIONICITY / AMNIONICITY
• If not possible to determine chorionicity by transbdominal or transvaginal ultrasound in the
routine setting, a second opinion should be sought from a tertiary referral center
• After 14 weeks, chorionicity is best determined using the same ultrasound signs in particular by
counting the membrane layers and noting the discordant fetal sex.
• At the time chorionicity is determined, amnionicity should also be determined and documented
6. LABELING OF TWIN FETUSES
• The labeling of twin fetuses should follow a reliable and consistent strategy and
should be documented clearly inorder to ensure consistent labeling during the
follow up scans.
• Describe each twin using as many features as possible so as to enable to identify them
accurately.
• Perinatal switch phenomenon – twins labeled as Twin A and Twin B during antenatal
scans may not necessarily delivered in that order.
7. ROUTINE MONITORING OF TWIN PREGNANCY
• UNCOMPLICATED DICHORIONIC TWIN
• First trimester scan
• Detailed second trimester scan and scans every 4 weeks
• COMPLICATED DICHORIONIC TWIN
• Depending on the condition and its severity
8. ULTRASOUND MONITORING
PATHWAY
UNCOMPLICATED
DICHORIONIC TWIN
PREGNANCY
Khalil A, Rodgers M, Baschat A, Bhide A, Gratacos E, Hecher K, Kilby MD, Lewi L,
Nicolaides KH, Oepkes D, Raine-Fenning N, Reed K, Salomon LJ, Sotiriadis A,
Thilaganathan B, Ville Y. ISUOG Practice Guidelines: role of ultrasound in twin
pregnancy. Ultrasound Obstet Gynecol 2016; 47: 247–263.
9. ROUTINE MONITORING OF TWIN PREGNANCY
• UNCOMPLICATED MONOCHORIONIC TWIN
• First trimester scan
• Every 2 weeks after 16 weeks (to detect TTTS and TAPS)
• COMPLICATED MONOCHORIONIC TWIN
• Depending on the condition and its severity
10. ULTRASOUND
MONITORING PATHWAY
UNCOMPLICATED
MONOCHORIONIC TWIN
Khalil A, Rodgers M, Baschat A, Bhide A, Gratacos E, Hecher K, Kilby MD, Lewi L, Nicolaides KH,
Oepkes D, Raine-Fenning N, Reed K, Salomon LJ, Sotiriadis A, Thilaganathan B, Ville Y. ISUOG
Practice Guidelines: role of ultrasound in twin pregnancy. Ultrasound Obstet Gynecol 2016; 47:
11. IN EACH ULTRASOUND ASSESSMENT:
• Fetal biometry
• Amniotic fluid volume
• Umbilical artery doppler- from 20 weeks for both twins
• Discordance in estimated fetal weight from 20 weeks
12. MONOCHORIONIC TWINS
• Fetal biometry
• Amniotic fluid volume
• Umbilical artery doppler- from 20 weeks for both twins
• Discordance in estimated fetal weight from 20 weeks
• Cervical length assessment at 20-24 weeks may lead to better prediction of preterm birth
(less than 25 mm in asymptomatic twin)
• Middle cerebral artery PSV – peak systolic velocity - from 20 weeks ( screen for
TAPS)
• Monochorionic diamniotic twins – amniotic fluid volume (deepest vertical
pocket) to screen for TTTS
13. SCREENING FOR CHROMOSOMAL ABNORMALITIES
• First trimester screen for aneuploidy –
• nuchal translucency thickness
• Free beta HCG
• Pregnancy-associated plasma protein-A
• In case of vanishing twin – if there is still a measurable fetal pole, NT alone, in combination with
maternal age, should be used for risk estimation
• Detection rate of non invasive prenatal test- may be lower in twins than in singletons, but data are
still limited. DR for trisomy 21 in singleton – 99% FPR – 0.1%; DR for Trisomy 21 in twins 94.4%
and FPR - 0%
• Invasive testing-
• Pregnancy loss rate: CVS - 3.85%; Amniocentesis – 3.1%
14. IMPLICATION OF DISCORDANCE IN NT OR CRL
IN THE FIRST TRIMESTER
• The management of twin pregnancy with CRL discordance ≥ 10% or of NT
discordance ≥ 20%.
• Detailed ultrasound assessment and testing for karyotype abnormalities.
• 25% risk of fetal abnormalities for CRL discordance >10%
• CRL discordance at 7 + 0 to 9 + 6 weeks’ gestation is a predictor of the risk of
single fetal demise in the first trimester (DR of 74% for a FPR of 5%)
• An abnormal DV will pick up only 38% of all pregnancies that subsequently
develop TTTS, and, of those predicted to be at high risk, only 30% will ultimately
develop TTTS
15. SCREENING FOR STRUCTURAL ABNORMALITIES
• Assessed for the presence of any major
anomalies at the first trimester scan
Salomon LJ, Alfirevic Z, Bilardo CM, Chalouhi GE, Ghi T, Kagan KO, Lau TK, Papageorghiou AT, Raine-Fenning NJ, Stirnemann J, Suresh S, Tabor A, Timor-
Tritsch IE, Toi A, Yeo G. ISUOG Practice Guidelines: performance of first-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol 2013; 41: 102–113.’.
16. SCREENING FOR STRUCTURAL ABNORMALITIES
• Routine second trimester anomaly scan (18-20 weeks)
• Cardiac screening assessment should be performed in monochorionic twins
• Laterality, Situs, 4 chamber, ventricular outflow tract and aortic arch views.
• IMPORTANT TO MAKE THE WOMAN AWARE OF THE LIMITATIONS OF ULTRASOUND
SCREEENING, WHICH VARY ACCORDING TO THE TYPE OF ANOMALY
17. SCREENING FOR RISK OF PRETERM BIRTH
• Cervical length measurement is the preferred method
• 25 mm is the cut-off most commonly used in the second trimester
• Cervical length of <25 mm at 18-24 weeks – moderate predictor of preterm birth before
34 weeks, but not before 37 weeks
• Cervical length of <20 mm at 20-24 weeks – most accurate predictor of preterm birth
before 32 and before 34 weeks
• No effective strategy to prevent preterm birth in these women.
• Bed rest, progesterone therapy, Arabin cervical pessary or oral tocolytics do not reduce the risk
of preterm delivery
• Progesterone therapy might reduce the risk of neonatal morbidity and mortality.
18. SCREENING, DIAGNOSIS AND MANAGEMENT OF
FETAL GROWTH RESTRICTION
• Selective FGR - one fetus has EFW <10th percentile and the intertwin EFW discordance is
>25%
• A discordance cut off of 20% - increased risk of adverse outcome
SCREENING:
• Combination of head, abdomen and femur measurements performs best in calculating
EFW
• Intertwin discordance > 25% referral should be made to a tertiary fetal medicine center.
• Once diagnosed – detailed anomaly scan and screening for viral infections (CMV, rubella and
toxoplasmosis)
• Amniocentesis – required to exclude chromosomal abnormalities
19. CLASSIFICATION OF MONOCHORIONIC PREGNANCIES COMPLICATED
BY SELECTIVE INTRAUTERINE GROWTH RESTRICTION
Type of sFGR Findings in the UMA Outcome
I Positive end diastolic flow • 90% survival
• In-utero mortality rates up to 40%
II Absent or reversed end diastolic
flow (AREDF)
• High risk of intrauterine death of growth restricted twin and
or very preterm delivery with associated risk of
neurodevelopmental delay
• IUD of either twin in up to 29%
• 15% risk of neurological sequelae if born prior to 30 weeks
III Cyclical / intermittent pattern of
AREDF
• 10 to 20% risk of unpredictable sudden death of FGR fetus
even with ultrasound features have been stable
• Up to 20% rate of neurological morbidity in surviving larger
twin
Gratacos E., Lewi L, Munoz B, Acosta-Rojas R, Hernandez-Andrade E, Martinez JM, Carreras E Deprest JA, Classification for selective intrauterine
growth restriction in monochorionic pregnancies according to umbilical artery Doppler Flow in the smaller twin, Ultrasound Obstet Gynecol 2007;
20. DICHORIONIC TWIN PREGNANCY COMPLICATED
BY SFGR
• Follow-up visits could be less frequent, as delivery is usually not recommended
before 32–34 weeks’ gestation.
• fetal Doppler should be assessed approximately every 2 weeks, depending on the
severity.
• Management of these cases is complex and should be coordinated by a tertiary-
level fetal medicine center
21. MONOCHORIONIC TWIN PREGNANCY COMPLICATED BY
SFGR
• fetal growth should be assessed at least every 2 weeks, and fetal Doppler
(umbilical artery and MCA) at least weekly.
• If the umbilical artery Doppler is abnormal, assessment of the DV blood flow
should be undertaken.
• The aim in managing these pregnancies is to prolong the pregnancy at least until
viability is achieved, while at the same time avoiding single IUD with its associated
serious consequences for the surviving cotwin.
22. MONOCHORIONIC TWIN PREGNANCY COMPLICATED
BY SFGR
• The timing of delivery based on assessment of fetal wellbeing, interval growth,
biophysical profile, DV waveform and/or computerized cardiotocography (CTG)
• Incidence of severe cerebral injury in monochorionic twins complicated by sFGR is
approximately 10% and is associated with abnormal umbilical artery Doppler,
single IUD and low gestational age at birth.
• Risks of neonatal morbidity (38% vs 19%), particularly respiratory distress
syndrome (32% vs 6%) and cerebral lesions, are higher in the larger than in the
smaller co-twin
23. MANAGING THE SURVIVING TWIN AFTER DEMISE
OF ITS CO-TWIN
The following complications are found in monochorionic and dichorionic
pregnancies.
Complication Monochorionic Dichorionic
Death of the co-twin 15% 3%
Preterm delivery 68% 54%
Abnormal postnatal cranial imaging of the surviving
co-twin
34% 16%
Neurodevelopmental impairment of the surviving co-
twin
26% 2%
Khalil A, Rodgers M, Baschat A, Bhide A, Gratacos E, Hecher K, Kilby MD, Lewi L, Nicolaides KH, Oepkes D, Raine-Fenning N, Reed K,
Salomon LJ, Sotiriadis A, Thilaganathan B, Ville Y. ISUOG Practice Guidelines: role of ultrasound in twin pregnancy. Ultrasound Obstet
Gynecol 2016; 47: 247–263.
24. MANAGING THE SURVIVING TWIN AFTER DEMISE
OF ITS CO -TWIN
• Fetal doppler studies – Middle cerebral artery – Peak systolic velocity to search for
signs of fetal anemia in the surviving co-twin.
• Parents advised of the possibility long term neurologic damage.
• If the fetus is remote from term
• fetal biometry is done every 2-4 weeks
• cardiotocography, doppler of the UMA and MCA done every 2-4 weeks,
• single course of maternal glucocorticoids is given
• elective delivery is done at 34-36 weeks
• Normal MCA-PSV in the first few days after the demise of the co-twin is reassuring
25. ROLE OF DOPPLER ULTRASOUND IN COMPLICATIONS
UNIQUE TO MONOCHORIONIC TWIN PREGNANCY
• Twin to twin perfusion syndrome
• Twin Anemia Polycythemia sequence
• Twin reversed arterial perfusion sequence
• Monochorionic monoamniotic twins
26. TWIN TO TWIN PERFUSION SYNDROME /
OLIGOHYDRAMNIOS-POLYHYDRAMNIOS SEQUENCE
• Affects 10-15%of monochorionic pregnancy
• Unequal hemodynamic and amniotic fluid balance caused by vascular anastomoses between the
two fetal circulations in a single big placenta.
• Results to diminution of amniotic fluid in the donor twin (SVP of <2 cm.) and a small or
absent urinary bladder.
• Recipient twin has SVP of more than 8 cm and a large bladder
• Fetal growth discordance is common but not an integral aspect
• Pathognomonic sign is the appearance of the donor as the stuck twin contained within the
collapsed inter-twin membrane
27. Khalil A, Rodgers M, Baschat A, Bhide A, Gratacos E, Hecher K, Kilby MD, Lewi L, Nicolaides KH, Oepkes D,
Raine-Fenning N, Reed K, Salomon LJ, Sotiriadis A, Thilaganathan B, Ville Y. ISUOG Practice Guidelines: role of
ultrasound in twin pregnancy. Ultrasound Obstet Gynecol 2016; 47: 247–263.
Quintero staging does not
always predict accurately
outcome or chronological
evolution of TTTS,
it remains the classification
system of choice
TWIN TO TWIN PERFUSION SYNDROME /
OLIGOHYDRAMNIOS-POLYHYDRAMNIOS SEQUENCE
28. TWIN TO TWIN PERFUSION SYNDROME /
OLIGOHYDRAMNIOS-POLYHYDRAMNIOS SEQUENCE
• In monochorionic twin pregnancy, screening for TTTS should start at 16 weeks, with
scans repeated every 2 weeks thereafter
• At every scan, note and record
• evidence of membrane folding and
• measure the DVP of amniotic fluid for each fetus.
If significant inequality in DVP exists or there is membrane infolding, then more frequent
ultrasound surveillance may be warranted
• less common in MCMA, compared with MCDA, twin pregnancy;
• diagnostic features include polyhydramnios in the common amniotic sac and
discordant bladder sizes.
29. TWIN TO TWIN PERFUSION SYNDROME /
OLIGOHYDRAMNIOS-POLYHYDRAMNIOS SEQUENCE
• Monochorionic twin pregnancies with uncomplicated amniotic fluid discordance
can be followed up on a weekly basis to exclude progression to TTTS
30. TREATMENT OF TTTS
• Laser ablation is the treatment of choice for TTTS at Quintero stages II and above
• Conservative management with close surveillance or laser ablation can be
considered for Quintero stage I
• When laser treatment is not available, serial amnioreduction is an acceptable
alternative after 26 weeks’ gestation
31. TWIN ANEMIA-POLYCYTHEMIA SEQUENCE (TAPS)
• The incidence occurring spontaneously in MCDA twins is up to 5%.
• may complicate up to 13% of cases of TTTS following laser ablation.
• TAPS is believed to be due to the presence of miniscule arteriovenous
anastomoses (< 1 mm) which allow slow transfusion of blood from the
donor to the recipient, leading to highly discordant hemoglobin
concentrations at birth
• The prenatal diagnosis of TAPS is based on the finding of discordant MCA
Doppler abnormalities
• There is little evidence about the outcome and optimal management of
TAPS
32. Khalil A, Rodgers M, Baschat A, Bhide A, Gratacos E, Hecher K, Kilby MD, Lewi L, Nicolaides KH, Oepkes D, Raine-Fenning N, Reed K, Salomon
LJ, Sotiriadis A, Thilaganathan B, Ville Y. ISUOG Practice Guidelines: role of ultrasound in twin pregnancy. Ultrasound Obstet Gynecol 2016; 47:
247–263.
33. • The polycythemic twin might have a ‘starry sky’
appearance of the liver pattern due to
diminished echogenicity of the liver parenchyma
and increased brightness of the portal venule
walls.
• Ultrasound image showing a starry sky liver in a
TAPS recipient with clearly identified portal
venules (stars) and diminished parenchymal
echogenicity (sky) that accentuates the portal
venule walls.
TWIN ANEMIA-POLYCYTHEMIA SEQUENCE (TAPS)
34. TWIN ANEMIA-POLYCYTHEMIA SEQUENCE (TAPS)
• Ultrasound image of a TAPS placenta showing
a difference in placental thickness and
echodensity. On the left side of the image the
hydropic and echogenic placental share of the
anemic donor and on the right side the normal
aspect of the placenta of the recipient is
depicted.
35. FLOWCHART WITH ANTENATAL MANAGEMENT
OPTIONS FOR TAPS
Tollenaar, L., Slaghekke, F., Middeldorp, J., Klumper, F., Haak, M., Oepkes, D., & Lopriore, E. (2016). Twin Anemia
Polycythemia Sequence: Current Views on Pathogenesis, Diagnostic Criteria, Perinatal Management, and Outcome. Tw
Research and Human Genetics, 19(3), 222-233. doi:10.1017/thg.2016.18
36. ALGORITHM FOR DIFFERENTIAL DIAGNOSIS IN MC TWINS
WITH APPARENT DISCREPANCY IN AF OR FETAL SIZE
Gratacós, E., Martinez, J.M., & Ortiz, J.U. (2012). A systematic approach to the differential diagnosis
and management of the complications of monochorionic twin pregnancies. Fetal diagnosis and
37. TWIN REVERSED ARTERIAL PERFUSION
(TRAP SEQUENCE)
• TRAP sequence is a rare complication of monochorionic twin pregnancy (1% of monochorionic
twin pregnancies and 1 in 35 000 pregnancies overall).
• It is 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 arterioarterial anastomoses, usually
through a common cord insertion site
• This characteristic vascular arrangement predisposes 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
39. TWIN REVERSED ARTERIAL PERFUSION
(TRAP SEQUENCE)
• Pump twin maintains a normal pattern of fetal circulation.
• A portion of its cardiac output travels through placental arterial-arterial anastomoses to the umbilical
artery and eventually the systemic circulation of the recipient co-twin, thus creating a reversed
circulation in this twin.
• Acardiac twin lacks a functional heart whose pumping would normally provide forward flow and high
systemic pressure.
• Presence of arterial –arterial anastomoses allows blood to be pumped from the normal twin to the
acardiac twin without passing through a capillary bed. Venous- venous and arterio-venous
anastomoses also occur.
• Abnormal circulatory pattern provides perfusion of deoxygenated blood from the pump twin to the
lower half of the recipient twin via its iliac arteries but poor perfusion of the upper torso and head.
Unequal vascular perfusion from the pump twin may contribute to the evolution of a variety of
structural abnormalities in the recipient twin
40. TWIN REVERSED ARTERIAL PERFUSION
(TRAP SEQUENCE)
• Antenatal diagnosis may be made by the absence of the heart on ultrasound and
revealing vascular anastomosis with doppler despite present of trunk and extremity
movement in the twin that has multiple anomalies.
• Prenatal diagnosis of acardiac fetus may be made with ultrasound at first trimester
• Doppler show pathognomonic features flow of arterial –arterial anastomosis
• Definitive diagnosis : color doppler demonstrating reversal of blood flow within the
abnormal fetus
• Blood flow pattern reveals a paradoxical direction of arterial flow towards rather than
away from the acardiac twin and retrograde flow in the acardiac twins abdominal
aorta.
41. TWIN REVERSED ARTERIAL PERFUSION
(TRAP SEQUENCE)
• After diagnosis: fetal hemodynamic function should be assessed by fetal
echocardiography
• Hydrops in the pump twin is a poor prognostic feature
• Estimation of weight ratio of the acardiac to the pump twin should be established
42. INDICATORS OF POOR PROGNOSIS FOR TWIN
REVERSED ARTERIAL PERFUSION (TRAP SEQUENCE)
• Ratio of weight of the acardiac twin/weight of the pump twin greater than 0.70.
• weight (grams) = (-1.66 x longest length[cm]) + (1.21 x longest length[cm])
• Polyhydramnios (maximum vertical pocket ≥8 cm)
• Cardiac failure in the pump twin may be marked by abnormal Doppler studies including persistent
absent or reversed diastolic blood flow in the umbilical artery, pulsatile blood flow in the umbilical
vein, and/or reversed blood flow in the ductus venosus.
Ratio of Acardiac twin to the pump twin Risk of preterm delivery (%) Risk of polyhydramnios (%)
>0.70 90 40
<0.70 75 30
Moore, Thomas R. et al. Perinatal outcome of forty-nine pregnancies complicated by acardiac
twinning American Journal of Obstetrics & Gynecology , Volume 163 , Issue 3 , 907 - 912
43. INDICATORS OF POOR PROGNOSIS FOR TWIN
REVERSED ARTERIAL PERFUSION (TRAP SEQUENCE)
• Increase in relative size of the acardiac twin. The longest linear measurement
(length) of the acardiac twin is measured as an approximation of its growth.
• abdominal circumference (including the skin) of the acardiac twin at the level of
the stomach can be measured and compared to that of the pump twin.
• An acardiac pump twin ratio ≥1.0 is considered significant (ie, abdominal
circumference of the acardiac twin equal to or greater than that of the pump twin).
• Hydrops in the pump twin
• Monoamniotic pregnancy (cord entanglement risk)
44. TWIN REVERSED ARTERIAL PERFUSION
(TRAP SEQUENCE)
• weekly ultrasound surveillance of the pump twin to look for signs of fetal hydrops and
abnormal
• Doppler studies of the umbilical artery, umbilical vein and ductus venosus.
• Ultrasound surveillance is increased to two times a week if there is evidence of pre-
hydrops (ie, fluid in only one cavity-ascites, pleural effusion).
• Given the increased risk of preterm birth, antenatal corticosteroid administration
generally should be provided to all patients between 23 and 34 weeks of gestation.
• The timing within this range is based on evidence of preterm labor or impending
compromise of the pump twin which might necessitate delivery.
45. TWIN REVERSED ARTERIAL PERFUSION
(TRAP SEQUENCE)
• deliver TRAP pregnancies at 34 to 36 weeks of gestation.
• The timing of delivery within this range depends on the patient’s clinical scenario
and whether there are indications of compromise in the pump twin, which would
prompt earlier delivery.
• Cesarean delivery is indicated if there is a malpresentation, nonreassuring fetal
heart rate pattern or low biophysical profile score for the pump twin,
monoamniotic twins, or other contraindications to vaginal birth (eg, placenta
previa).
46. MONOCHORIONIC MONOAMNIONIC TWINS
• Monoamniotic twins are the least common type of twins, occurring just 1:10,000
pregnancies and complicating only 1%-5% of monozygotic twin gestations.
• It is the result of a single embryo dividing between 8-12 days post-fertilization.
• The perinatal mortality rate is very high, ranging between 10% - 40% (Murata, Van
Mieghem) . Most fetal losses are due to spontaneous miscarriage and congenital
anomalies
• TTTS and cerebral injury occurs in as much as 6% of cases
• Increased risk for intrauterine death compared to other types of twinning.
47. MONOCHORIONIC MONOAMNIONIC TWINS
• Because the frequency is so low, the management of monoamniotic
twins is controversial due to the lack of a strong evidence base for
antepartum management.
48. MONOCHORIONIC MONOAMNIONIC TWINS
ULTRASOUND CRITERIA:
• Same sex twins
• No evidence of dividing membrane, seen on at least two consecutive ultrasound
examinations
• Single placenta
• Normal amniotic fluid volume with 2 free-floating fetuses
• Unrestricted fetal movement (no evidence of stuck twin or conjoined twins)
• Cord entanglement, as seen by color Doppler and/or 3D ultrasound
• One yolk sac (first trimester)
• Visualization of 2 cord insertions into the placenta in close proximity is suggestive of
monoamnionicity.
50. MANAGEMENT OPTIONS AT VIABILITY:
• There is no consensus regarding optimal management of monoamniotic
twin pregnancies.
• These pregnancies warrant a high level of surveillance due to the high rates of
fetal loss, which is often due to cord entanglement.
• Patients should be informed of the risks and benefits of inpatient vs. outpatient
management and should be active participants in developing the surveillance
plan.
51. • Intensive inpatient management to begin at 26-28 weeks gestational age
1. Three times daily monitoring for two hours each time (total 6 hours CEFM daily)
2. Weekly biophysical profile with umbilical artery Doppler studies
3. Growth scan every 3 weeks
• Intensive outpatient management to begin at 26-28 weeks gestational age
1. May only be offered to patients with reliable transportation, who live within a
relatively close proximity to the office and who have the ability to attend visits regularly
2. Prolonged non-stress testing for one hour 4-7 times weekly
3. Twice weekly biophysical profile
4. Admission if any testing is non-reassuring, or if patient desires
52. • Evaluate early (24 to 28 weeks gestation) hospitalization of monoamniotic twins, with close fetal
surveillance, and delivery at 32 to 34 weeks gestation, would significantly improve the perinatal
morbidity and mortality compared with an outpatient management strategy.
• A multicenter, retrospective record review was undertaken. Records of all monoamniotic twins were
collected for a 10-year period. Monoamniotic twins were identified using intensive care nursery,
ultrasound, and pathology records. Data were collected on inpatient versus outpatient management
strategies and the perinatal/maternal outcomes and complications. Twenty-three sets of
monoamniotic twins were included in the study.
• Eleven sets were managed using an inpatient strategy and 12 sets were managed using an outpatient
strategy.
• There were no fetal deaths in the inpatient group and there were three fetal deaths in the outpatient
group.
• Inpatient management of monoamniotic twins should be considered.
INPATIENT VERSUS OUTPATIENT MANAGEMENT OF MONOAMNIOTIC TWINS
AND OUTCOMES
M DeFalco, Lisa & Sciscione, Anthony & Megerian, Garo & Tolosa, Jorge & Macones, George & O'Shea, Anne & A Pollock,
Marjorie. (2006). Inpatient versus Outpatient Management of Monoamniotic Twins and Outcomes. American journal of
perinatology. 23. 205-11. 10.1055/s-2006-934091.
53. Dias T, Thilaganathan B, Bhide A. Monoamniotic twin pregnancy. The Obstetrician &
Gynaecologist 2012;14:71–78.
54.
55. • Recommend routine (prophylactic) antenatal corticosteroids at 26-28 weeks
gestational age, or earlier if signs of fetal compromise are present.
• A second full course can be repeated prior to delivery at 32-34 weeks gestational age
or sooner if 4 weeks have elapsed since the first course and delivery is imminent.
Cesarean section at 32-34 weeks (sooner with complications);
• For single intrauterine death <23 weeks, outpatient observation.
• For single intrauterine death >24 weeks, admit for evaluation and CEFM. There
should be a low threshold for delivery of surviving twin
56. MONOCHORIONIC MONOAMNIONIC TWINS
Timing of delivery is a balance between the risk of preterm birth and the risk
of intrauterine death at a given gestation.
The basis for timed elective delivery is to prevent cord related deaths .
Majority uses cesarean birth as the preferred delivery mode for monoamniotic
twins
The disadvantage of using the smaller CRL is the potential of the operator believing that the larger twin is large for gestational age and therefore being falsely reassured that the smaller twin is still growing appropriately.
Chorionicity should be determnined between 11 and 13 weeks 6days using the membrane thickness at the site of insetion of the amniotic membrane into the placenta, identifying the T-sign or lambda sign and the number of placental masses visualized.
Perinatal switch phenomenon – twins labeled as twin a and twin b during antenatal scans may not necessarily delivered in that order. It is important to alert parents and healthcare professionals attending the delivery, particularly in pregnancies in which the twins are discordant for structural abnormalities that are not obvious by external examination.
In such cases, an ultrasound scan should be performed just prior to delivery and also before instigating any specific neonatal intervention.
In case of vanishing twin, if there is still a measurable fetal pole, B-HCG and PAPP-A measurements are biased and NT alone should be used for risk estimation.
The risk of Trisomy 21 in monochorionic twin pregnancy is calculated per pregnancy based on the average risk of both fetuses (the twins share the same karyotype), whereas in dichorionic twin pregnancy the risk is calculated per fetus ( as around 90% are dizygotic so have different karyotypes).
DR for Down syndrome may be lower in twin compared with singleton pregnancy. However, a recent meta-analysis reported similar performance (89% for singletons, 86% for dichorionic twins and 87% for monochorionic twins, at a false positive rate of 5%).
The risk of fetal abnormalities was found to be 25% in pregnancies with CRL discordance ≥ 10%, compared with 4% in pregnancies with CRL discordance < 10%.
The risk of fetal anomaly is greater in twin compared with singleton pregnancy.
As per rate, dizygotic twins is probably the same as that in singletons whereas it is 2-3x higher in monozygotic twins.
In around 1:25 dichorionic ; 1 in 15 MCDA and 1 in 6 monoamniotic twin, there is a major congenital anomaly that typically affects only one twin.
Therefore: screening for anomalies should be considered in monochorionic twin pregnancy, bearing in mind that brain and cardiac abnormalities might become more obvious in the third trimester.
Specific twin growth charts should be used for documenting, and monitoring growth in twin pregnancies. However, the use of specific twin for growth charts is controversial due to concern that the reduced growth in the third trimester observed in most twin pregnancies might be caused by some degree of placental insufficiency.
Selective fetal growth restriction in monochorionic twin pregnancy occurs mainly due to unequal sharing of the placental mass and vasculature.
As the risk of IUD in these pregnancies is increased, delivery might be indicated even before abnormalities in the DV Doppler or the computerized CTG become evident.
When one monochorionic twin dies in utero, the surviving twin may then lose part of its circulating volume to the dead twin, leading to potentially severe hypotension in the survivor. This can lead to hypoperfusion of the brain and other organs, which can cause brain damage or death.
The most serious consequence of a death of a fetus in twin pregnancy is the subsequent demise of the other fetus.
Severe hypotension may occur in the surviving twin because part of its blood volume is diverted to the dead twin. Thus the brain and other critical organs suffer from significant hypotension resulting in brain damage or death.
Parents advised of the possibility long term neurologic damage which may have started already such that even if an immediate cesarean delivery is done, the surviving twin could already have been injured.
If the fetus is remote from term fetal biometry is done every 2-4 weeks and cardiotocography, doppler of the UMA and MCA done every 2-4 weeks, single course of maternal glucocorticoids is given and elective delivery is done at 34-36 weeks
Normal MCA-PSV in the first few days after the demise of the co-twin is reassuring since fetal anemia of the surviving twin usually does not ensure.
Ultrasound or MRI of the brain of the surviving twin should be done after 4-6 weeks to assess brain damage
At 2 years of age, neurodevelopment of the child must be assessed.
Starting at 16 weeks, and every 2 weeks thereafter, monochorionic pregnancies should be scanned to watch out for the early findings of TTTS.
Presence of amniotic fluid volume discordance in an uncomplicated monochorionic twin pregnancy warrants a weekly scanning to watch our for progression to TTTS.
As long as the discordance in amniotic fluid falls within the normal range and UMA doppler findings ae normal, the outcome is good with overall survival of 93%, likewise a low risk for progression to severe TTTS.
In order to screen for TAPS, the MCA-PSV should be measured from 20 weeks onwards in both fetuses, and during the follow-up of cases treated for TTTS.
Prevention of TAPS by modification of the fetoscopic laser ablation technique remains the best way to prevent morbidity
After diagnosis of TRAP sequence, ratio of weight of the acardiac twin to pump twin should be considered to predict fetal prognosis.
The weight of acardiac twin can be calculated from its longest length by using following formula: weight (grams) = (-1.66 x longest length) + 1.21x (longest length)2 [7].
Otherwise, ratio of abdominal circumference of acardiac twin to normal twin can be measured to predict fetal outcome and its ratio of ≥1.0 is considered significant [7].
According to Moore et al., when the ratio of the weight of the acardiac twin to that of the pump twin exceeded 0.70, the risks of preterm delivery and hydramnios were 90 and 40%, respectively [7].
Fetal surveillance from 16 weeks onwards with doppler studies of middle cerebral artery help in early diagnosis of anemia in pump twin. Further, reversed diastolic blood flow in the umbilical artery and umbilical vein’s pulsatile blood flow, or abnormal ductus venosus blood flow in the pump twin are indicators of impending intrauterine fetal demise [8].
Other poor prognostic factors for normal twin are risk of cord entanglement and hydramnios in monoamniotic twin pregnancy.
Monoamniotic twin gestations are uncommon and most institutions will have limited experience in their direct management.
All published data are observational and open to individual practice and publication bias.
In the absence of the intertwin membrane, it is best confirmed by transvaginal scan.
Presence of cord entanglement which is universal in MCMA twin pregnancy using color and pulsed wave doppler ultrasound.
Using pulsed wave doppler, 2 distinct arterial waveform patterns with different heart rates are seen within the same sampling gate
Pulsed wave Doppler demonstration of the ‘galloping’ heart rates of monoamniotic twins before 12 completed weeks of gestation, confirming cord entanglement. One fetus had a heart rate of 148 and the other had a rate of 131 beats/min
Electronic fetal heart rate monitoring may be undertaken after fetal viability is achieved.
The rationale for the use of cardiotocography is that it may detect features of cord compression (bradycardia or repeated variable decelerations) before fetal demise ensues.
There is no evidence that this intervention is effective in preventing cord entanglement accidents and there is no consensus as to the optimal frequency of such monitoring (Table 4)
. Hospital admission from viability until delivery for monoamniotic twin pregnancy has also been reported. Heyborne et al.5 reported a 100% survival rate of inpatient versus 86% for outpatient-based management in a retrospective non-randomised cohort study. The authors used electronic fetal heart rate monitoring at variable frequency in both groups and did not explain how this form of monitoring would have prevented TTTS, which was responsible for the majority of outpatient losses in their study. In another retrospective analysis,7 a fetal survival of over 90% in nonanomalous twins was reported in both inpatient and outpatient groups. In the latter study,7 the outpatient group either had no monitoring or twice-weekly cardiotocography in a nonrandom allocation. Additionally, it is difficult to postulate how anything other than continuous cardiotocography throughoutthe antenatal period can diagnose imminent fetal demise early enough for effective intervention. Interestingly, improved perinatal survival has been reported in several series in which monoamniotic twins were managed on an outpatient basis.6, 1
Van Miegham, et al1 report the largest published series of monoamniotic twins to date. With four-times-a-week monitoring, the authors found a lower intrauterine fetal death rate than previously reported with outpatient care, although in our view it remains unacceptably high, with more than 1 in 18 fetuses lost.
The authors’ primary conclusions are that the optimal time for delivery is around 32 4/7 weeks of gestation and that inpatient and outpatient care yield similar outcomes.
Monoamniotic twins remain a clinical challenge, and strong conclusions should not be drawn from a single study.
We believe that women with monoamniotic twin
pregnancies should be referred to highly specialized tertiary care units and that these units should implement local management protocols for surveillance and then publish their unselected outcomes
