dichorionic - diamniotic twins

A dichorionic diamniotic (DCDA) twin pregnancy is a type of twin pregnancy where each twin has its own chorionic and amniotic sacs. This type occurs most commonly with dizygotic twins, but may also occur with monozygotic twin pregnancies. This type of pregnancy may have characteristic findings on ultrasound.

Epidemiology

DCDA pregnancies account for the majority (~76%) of all twin pregnancies. They account for all dizygotic pregnancies and ~20% of monozygotic pregnancies.

Pathology

Etiology

With a dizygotic pregnancy, two ova are independently fertilised by two sperm leading to two zygotes.

With a monozygotic twin pregnancy, DCDA pregnancy results from the separation of the zygotes at ~1-4 days post fertilisation (morula) stage.

Radiographic features

Ultrasound

Sonographic assessment of chorionicity is most accurate in the first trimester.

First trimester

Features supporting a DCDA pregnancy:

• presence of two gestational sacs with a thick echogenic chorion surrounding each embryo
• a thick inter-twin membrane (often taken as > 2 mm)
• twin peak sign (lambda (λ) sign)
• two yolk sacs may be seen (this, however, does not differentiate a DCDA pregnancy from a monochorionic diamniotic (MCDA) pregnancy)

Second trimester

• when there is no placental fusion, two separate placental sites may be seen
• a finding of two different genders for each twin is a definitive feature for a dizygotic pregnancy which in turn will invariably mean a DCDA pregnancy

If the twins are of the same gender then it is extremely difficult if not impossible to determine if they are monozygotic or dizygotic on ultrasound.

Complications

While the complication rate is still much higher with twins than with a singleton pregnancy, a DCDA pregnancy carries the lowest rate of complications amongst twin pregnancies. Such recognized complications include:

• increased risk of intrauterine growth restriction (IUGR)
• placenta-related problems
  • increased risk of velamentous cord insertion
  • increased risk of marginal cord insertion
  • increased incidence of placenta previa spectrum

Siehe auch:

• marginal cord insertion
• Dottersack
• Zwillingsschwangerschaft
• Placenta praevia
• inter twin membrane
• monochoriale-diamniote Zwillingsschwangerschaft
• placental fusion
• Insertio velamentosa
• twin peak sign
• monozygotic
• gestational sacs
• intra uterine growth restriction (IUGR)
• dizygotic

und weiter:

• obstetric curriculum
• sonographic values in obstetrics and gynaecology
• amniotic fluid discordance
• monozygotic twin pregnancy
• MCDA pregnancy
• monochoriale-monoamniote Zwillingsschwangerschaft
• dizygotic twin pregnancy
• dichorionic twin pregnancy
• Mehrlingsschwangerschaft