Monozygotic twin pregnancy
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View Jeremy Jones's current disclosures- Monozygotic twins
- Identical twins
- MZ twins
A monozygotic (MZ) twin pregnancy results from the division of single zygote following fertilisation and shares similar genetic materials. These twins are therefore always of the same gender.
On this page:
Epidemiology
Monozygotic twins account for approximately 30% of all twin pregnancies 1. The estimated incidence is at ~1 in 250 births with little racial variation for this subtype 3 (cf. dizygotic twin pregnancy).
Physiology
Depending on the time of division of the zygote, there can be many possibilities
- division at 1-4 days (morula) results in dichorionic-diamniotic twins (di-di) (DCDA) : 20% of monozygotic twin pregnancies
- division at 4-8 days (blastocyst) results in monochorionic-diamniotic twins (mono-di) (MCDA) : 75% of monozygotic twin pregnancies
- division at 1-2 weeks results in monochorionic-monoamniotic twins (mono-mono) (MCMA): 5% of monozygotic twin pregnancies
- division at >2 weeks results in conjoined twins: <1% of monozygotic twin pregnancies
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Related pathology
Prenatal diagnosis of chorionicity is important as monochorionic pregnancies have increased rates and severity of all types of obstetric complications when compared with dichorionic pregnancies. Monozygotic twins have a higher rate of fetal anomalies although they tend to be discordant-only affecting one twin despite identical genetic makeup.
Monochorionic twin pregnancies share the one placenta and are therefore prone to hemodynamic complications such as:
- twin-twin transfusion
- twin reversed arterial perfusion sequence
- twin embolization syndrome
- acardiac twin
- demise of co-twin
Monochorionic monoamniotic twins also carry additional cord related complications such as:
See also
References
- 1. Trop I. The twin peak sign. Radiology. 2001;220 (1): 68-9. Radiology (full text) - Pubmed citation
- 2. Dähnert W. Radiology Review Manual. Lippincott Williams & Wilkins. (2011) ISBN:1609139437. Read it at Google Books - Find it at Amazon
- 3. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
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