Monochorionic diamniotic twin pregnancy is a type of twin pregnancy where each twin has its own amniotic sacs but both share one chorion

2. Teratology

3. • Monochorionic diamniotic twin pregnancy is a type of twin pregnancy
where each twin
has its own amniotic sacs
but both share one chorion

8. Pathophysiology:
• An MCDA twin pregnancy result from the fertilization of
one ovum by one sperm.
• The resulting zygote forms single blastocyst which contain
two the inner cell masses (embryoblast )
but single outer cell mass .

9. Pathophysiology:
• Single outer cell mass forms
a single chorionic sac and single placenta
• but two inner cell masses produce
two yolk sacs and two amniotic sacs.

10. Types of Monozygotic Twins
Related to Time of Division After Ovum Fertilization
Chorion Amnion Time to Division (Days) Frequency
Dichorionic Diamniotic 0-3 25%
Monochorionic Diamniotic 4-8 75%
Monochorionic Monoamniotic 9-12 ~1%
Monochorionic Monoamniotic 13-15 Rare
conjoined twins

11. Radiographic features

12. 1st trimester early

13. 1st trimester dichorionic diamniotic twin
Dichorionic twin pregnancy at 5 weeks 3 days.
Two round sonolucent sacs with a brightly echogenic rim are clearly visible in
the thick decidua.

14. 1st trimester monochorionic diamniotic twin
At 6 postmenstrual weeks a single chorionic sac is seen containing two yolk sacs:
the diagnosis of monochorionic twin pregnancy can be done; it is not possible yet to diagnose
amnioticity( monochorionic or diamniotic )

15. 1st trimester
Monochorionic twin pregnancy
At 6 postmenstrual weeks a single chorionic sac is seen
containing two yolk sacs: the diagnosis of
monochorionic twin pregnancy can be done;
it is not possible yet to diagnose amnioticity.
Dichorionic twin pregnancy
at 5 weeks 3 days.
Two round sonolucent sacs with a brightly
echogenic rim are clearly visible
in the thick decidua.

16. Ultrasound First trimester early
• shows a twin pregnancy with a single gestational sac, and
almost always two separate yolk sacs (differentiating from
an MCMA pregnancy)

17. Ultrasound First trimester late
• T-sign of the intertwin membrane
• a thin inter-twin membrane may be seen but appears very thin without
intervening chorion (often taken as <2 mm): differentiating from
a DCDA pregnancy (although this assessment becomes increasingly difficult with
the progression of pregnancy)

18. 1st trimester late

21. Monochorionic diamniotic twin pregnancy Dichorionic diamniotic twin pregnancy

22. Second and third trimesters
• Findings noted on a second trimester scan include:
• the number of placental masses, thickness of the membrane, and the
presence/absence of the twin-peak sign are still viable options for
determining chorionicity
• fetal sex : almost always the same sex
• Negative findings:
• absent twin peak sign: differentiating from a DCDA pregnancy

25. Complications
• Potential complications that can occur
with this type of pregnancy include:
• problems related to abnormal placental
vascular anastomoses
• twin to twin transfusion syndrome: can occur
in ~15 1 - 30 4 % of MCDA pregnancies
• twin embolization syndrome
• twin reversed arterial perfusion sequence:

26. Complications
• demise of one twin: often
associated with some adverse
outcome to the other twin

27. Complications
• placental insertion related
problems
• increased incidence
of velamentous cord insertion
• increased incidence of marginal cord
insertion (c.f singleton pregnancy)

28. Vascular anastomoses include 3 types:
arterioarterial (AA),
venovenous (VV) and
arteriovenous (AV) anastomoses.

29. • arterioarterial (AA), venovenous
(VV) anastomosis are superficial
with bidirectional blood flow and
directly linking the arteries and
veins of two umbilical cords,
• while AV anastomoses form at a
deep capillary level within shared
cotyledons and allow only
unidirectional blood flow.
Monochorionic Diamniotic Twin Pregnancies by Video
of Tara A Morgan, MD

31. Complications
• placental insertion
related problems

32. Thank you