GMCH Chandigarh - 2022
Obstetrics & Gynaecology
Easy
In Identical twin, where the fetuses share common chorion, the number of placenta is?
Appeared in: GMCH Chandigarh - 2022
Explanation
- The question specifies that the identical twins share a 'common chorion,' which by definition means the pregnancy is monochorionic.
- The chorion is the fetal membrane that forms the fetal side of the placenta.
- Therefore, a single, shared chorion (monochorionic) results in a single, shared placenta that nourishes both fetuses.
- This occurs when the fertilized egg splits between 3 to 13 days after fertilization, after the chorion has already begun to form.
Why Other Options Were Wrong
- Option B: Two separate placentas are characteristic of dichorionic pregnancies, where each fetus has its own chorion and placenta.
- Option C: More than two placentas is not a standard presentation for a twin pregnancy.
- Option D: This describes a situation in dichorionic pregnancies where two separate placentas implant close together and fuse. Although they may appear as one large placental mass on ultrasound, they remain two functionally separate placentas with a dividing membrane.
Related Visual
- Visual 1: Diagram - An illustration comparing dichorionic-diamniotic (two placentas), monochorionic-diamniotic (one placenta), and monochorionic-monoamniotic (one placenta) twin pregnancies. This visual directly clarifies the relationship between the number of chorions and placentas.
Clinical Relevance
- Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Placentation and chorionicity in multiple gestation pregnancies as background academic context rather than a clinical decision trigger.
- Determining chorionicity via early ultrasound is one of the most critical steps in managing a twin pregnancy. Monochorionic twins have a single shared placenta with vascular connections (anastomoses) between the fetuses.
- This shared circulation places monochorionic twins at a significantly higher risk for unique and serious complications, including Twin-to-Twin Transfusion Syndrome (TTTS), Twin Anemia-Polycythemia Sequence (TAPS), and selective Intrauterine Growth Restriction (sIUGR).
- Nurses must educate the expectant parents about the increased need for surveillance with frequent ultrasounds and to report warning signs like a sudden, rapid increase in abdominal size or a noticeable difference in fetal movements.
How to Approach the Question
- First, break down the question's key terms: 'Identical twin' and 'share common chorion'.
- Recognize that 'common chorion' is the definition of a 'monochorionic' pregnancy.
- Recall the basic embryology: the chorion is the fetal component of the placenta.
- Connect the terms: One chorion ('mono-chorionic') logically leads to one placenta.
- Evaluate the options based on this deduction. 'One' is the only answer that fits. The other options describe dichorionic pregnancies ('Two', 'Two and fused') or are incorrect ('More than two').
Concept Tested & Keywords
- Concept Tested: Placentation and chorionicity in multiple gestation pregnancies.
- Stem keywords: Identical twin, common chorion, number of placenta
- Lead-in keywords: is
Question ID
Q_MLIEVdgCLwnXU5wQ_Oz1
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