RRB Nsg. Superintendent-2026 (Shift -3rd)
Obstetrics & Gynaecology
Medium
A patient is diagnosed with monozygotic monoamniotic twins. What is the most accurate explanation for this diagnosis?
Appeared in: RRB Nsg. Superintendent-2026 (Shift -3rd)
Explanation
- The term 'monozygotic' indicates that the twins originate from a single fertilized egg (zygote).
- The term 'monoamniotic' signifies that both fetuses are contained within a single amniotic sac.
- Monoamniotic twins are inherently 'monochorionic,' meaning they also share a single placenta.
- This configuration results from a late division of the zygote, occurring 8-12 days after fertilization, after the chorion and amnion have already formed.
Why Other Options Were Wrong
- Option A: This describes dizygotic (fraternal) twins, who develop from two separate eggs fertilized by two separate sperm. They are not monozygotic.
- Option B: While these twins are monozygotic (from one egg), having separate placentas makes them dichorionic. The question specifies monoamniotic twins, who share a placenta.
- Option D: This describes dizygotic twins (from two eggs). Dizygotic twins have two separate placentas; while they can fuse and appear as one, they do not truly share a single placental structure and circulation.
Related Visual
- Visual 1: Diagram - Illustrate the four possible outcomes of twinning based on the timing of zygote division (Dichorionic-Diamniotic, Monochorionic-Diamniotic, Monochorionic-Monoamniotic, and Conjoined), showing the relationship between the fetuses, placentas, and amniotic sacs in each case.
Clinical Relevance
- Nursing practice connection: Use the key finding related to Twinning mechanisms and classification based on chorionicity and amnionicity to guide bedside assessment, documentation, and the next nursing action.
- Monozygotic, monoamniotic (MoMo) twin pregnancies are the highest-risk type of twin gestation, with a perinatal mortality rate as high as 50%.
- The primary risk is umbilical cord entanglement, which can cut off blood and oxygen supply to one or both fetuses. This necessitates intensive monitoring, often including inpatient admission for frequent fetal surveillance from 24-28 weeks gestation until delivery.
- What if the diagnosis was 'monochorionic, diamniotic' twins? The risk would still be elevated due to the shared placenta (risk of Twin-to-Twin Transfusion Syndrome), but the presence of a separating amniotic membrane would prevent cord entanglement, making it a less risky situation than a monoamniotic pregnancy.
How to Approach the Question
- First, break down the terminology in the question: 'monozygotic' and 'monoamniotic'.
- Recall or deduce the meaning: 'Mono-' means one, 'zygote' refers to the fertilized egg, and 'amnion' refers to the amniotic sac.
- Therefore, the question is asking for the definition of twins that come from one egg and are in one amniotic sac.
- Evaluate each option against this definition.
- Eliminate options that describe twins from 'two fertilized eggs' (dizygotic).
- Between the remaining monozygotic options, select the one that correctly describes sharing both the placenta (implied by monoamniotic) and the amniotic sac.
Concept Tested & Keywords
- Concept Tested: Twinning mechanisms and classification based on chorionicity and amnionicity.
- Stem keywords: monozygotic monoamniotic twins, diagnosis
- Lead-in keywords: most accurate explanation
Question ID
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Practise the full RRB Nsg. Superintendent-2026 (Shift -3rd)
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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