1. TWINS
WHAT DO I NEED TO KNOW
Mono Chorionic (MC)
Di Chorionic (DC)
Mono Amniotic (MA)
Di Amniotic (DA)
Riverside Guidelines
MAY 2012
2. DETERMIME CHORIONICITY/AMNIONICITY
IN THE 1 ST TRIMESTER
THIS CAN BE DIFFICULT TO DO IN MANY PATIENTS
THE NIH RECOMMENDS THAT ALL twins Undergo NT
ultrasound prior to 14 weeks whether
DC/DA or MC/DA
The patient does not have to undergo CPSP screening
analyte draw if they do not desire genetic screening
HOWEVER benefits of NT screening ultrasound alone
should be emphasized such as
• CHORIONICITY/AMNIONICITY will be validated
• EARLY ONSET TTTS CAN BE DETECTED
• STRUCTURAL DEFECTS ( cardiac/anatomical) have a
greater likelihood of being detected.
All of this information would impact the management of
the pregnancy for the benefit of the baby.
3. Twin Gestations
• The majority of significant fetal
complications are related to Mono
chorionicity
• Monochorionic complications
– Unequal placental sharing-IUGR
– Twin twin transfusion syndrome 15%
(TTTS)
– Twin anemia polycythemia syndrome
(TAPS) variant of TTTS without oligo
– Acardiac twin (TRAP)
– MonoAmniotic &/OR Conjoined
4. (MC) More Complications
Require More Surveillance
•Increased birth defects general structural & Cardiac (fetal echo)
•Neurologic morbidity ~5% cerebral palsy in uncomplicated (MC)
twins
•Perinatal mortality (RR~ 3.5) in MC twins compared to DC twins
• Stillbirth rates are significantly higher in
MC 4.5% versus DC 1.3% (RR 3.6)
•Neonatal death rates are also significantly higher
MC 3.2% versus DC 2.1% (RR 1.5)
•For these reasons, management protocols for MC twins require
more intensive surveillance including: Doppler, fetal growth, & and
amniotic fluid volume than standard of care protocols for DC twins.
5. DETERMIME CHORIONICITY/AMNIONICITY
IN THE 1 ST TRIMESTER
• Look for two separate placentas ( typically
one posterior and one anterior = (DC)
• If there is a “fused” single placenta Look
for the "twin peak” sign = (DC)
• “twin peak” sign is a triangular
projection of chorionic tissue projecting
between the amniotic sacs where they
intersect with the placenta.
6. DETERMIME CHORIONICITY/AMNIONICITY
IN THE 1 ST TRIMESTER
• If there is no triangular projection
(“V” )of tissue between the sacs and
the membranes appear thin (ie usually
difficult to see) and intersect the placenta
@ a right angle typically
• this is coined the
“T sign”= MononChorionic (MC)
7. Determination of Chorionicity
• Most accurate determination is between
8 to 14 weeks ( send for NT sono if not
sure)
• THERFORE DETERMIME
CHORIONICITY IN THE 1 ST
TRIMESTER
– One “fused” placenta
may be (DC) or (MC)
– Two separate placentas (DC)
• One fused placenta
• T Sign = Monochorionic (MC)
• Twin Peak Sign = Dichorionic (DC)
8. Determination of Amnionicty most
ACCURATE < 10 WEEKS
• 8 – 10 weeks EGA one yolk sac is almost
(unfortunately not 100% ) diagnostic for
MONOAMNIOTIC twins. If you think you have
Monoamniotic twins send for NT sono and MFM
consult to validate thin membrane present or not,
regardless of one or two yolk sacs visualized.
• THE EARLIER IN GESTATION THE MORE
ACCURATE THE DIAGNOSIS.
• To visualize the membrane in some MC twins will
frequently require “high level” technology
ultrasound machine.
9. Two fetuses / One yolk sac
Mono Amniotic
REFER TO MFM < 14 weeks
10. Dichorionic / Monochorionic
and ZYGOSITY
• Dizygotic twins 70% of all twins
• 99% are DC/DA
~ 15 % of DC placentas are Monozygotic
• Monozygotic twins 30 % of all twins
~1/3 are DC/ DA
~2/3 are MC / DA
~ 1% are MC /MA or MC/conjoined
11. Chorionicity
• Monozygotic
– Single fertilized ova splits into two embryos with
“identical” genes. Monochorionic placentas are
always monozygotic twins
– Approximately 15% of Dichorionic placentas are
monozygotic twins if the zygote splits ≤3 days
– SPLITS < 8 DAYS Diamniotic / Monochorionic
– SPLITS < 13 DAYS Monoamniotic / Monochorionic
– SPLITS > 13 DAYS Monoamniotic /Conjoined
22. MONOCHORIONIC
• DUE TO INCREASED COMPLICATIONS
• MFM SONOS Q 3 WEEKS STARTING @ 16
WEEKS INCREASING TO Q 1-2 WEEKS FOR
SOME IN 2nd / 3rd TRIMESTER
• START NST @ 32 WEEKS
• LOW THRESHOLD FOR DELIVERY WITH
“COMPLICATIONS” @ 32-36 WEEKS IF not
sure consider CONSULTING MFM
• NEW REGIONAL MFM RECOMMENDATIONS
DELIVER NO LATER THAN 37 COMPLETED
WEEKS IN UNCOMPLICATED MC TWINS
23. DICHORIONIC TWINS
• SONO IN RADIOLOGY EVERY 4-6
WEEKS IF NO IUGR/DISCORDANCE
• START SONOS @ 18-20 weeks ( eg
18-24-30-34)
• INCREASED RISK FOR IUFD
EXCEEEDS POSTNATAL RISK @ 38
WEEKS THERFORE ALL DELIVER
BEFORE 38 COMPLETED WEEKS.
24. CARDIAC DEFECTS & TWINS
•IVF Dichorionic & all Monochorionic twins
are at increased risk for cardiac defects
•AIUM recommends Fetal echo @ ~ 20
weeks for all Monochorionic twins and DC
IVF twins.
25.
26. NUTRITION
• Weight gain — Women carrying multiple gestations
should increase their daily dietary intake by ~ 600 kcal
over that of a nonpregnant woman
• The Institute of Medicine recommends the following
cumulative weight gain by term for women carrying
twins
• BMI <18.5 kg/m2 (underweight) — Minimum 37 lbs
• BMI 18.5 to 24.9 kg/m2 — weight gain 37 to 54 lbs
• BMI 25.0 to 29.9 kg/m2 — weight gain 31 to 50 lbs
• BMI ≥30.0 kg/m2 — weight gain 25 to 42 lbs
