Various types of chorionicity and amniosity (how the baby's sac looks) in monozygotic (one egg/identical) twins as a result of when the fertilized egg divides.
Monochorionic twins are monozygotic (identical) twins that share the same placenta. If the placenta is shared by more than two twins (see multiple birth), these are monochorionic multiples. Monochorionic twins occur in 0.3% of all pregnancies.[1] 75% of monozygotic twin pregnancies are monochorionic; the remaining 25% are dichorionic diamniotic.[2] If the placenta divides, this takes place after the third day after fertilization.[2]
Contents
- 1 Amniocity and zygosity
- 2 Diagnosis
- 3 Complications
- 4 See also
- 5 References
Amniocity and zygosity
Abdominal ultrasonography of monoamniotic twins at a gestational age of 15 weeks. There is no sign of any membrane between the fetuses. A coronal plane is shown of the twin at left, and a sagittal plane of parts of the upper thorax and head is shown of the twin at right.
Monochorionic twins generally have two amniotic sacs (called Monochorionic-Diamniotic "MoDi"), but sometimes, in the case of monoamniotic twins (Monochorionic-Monoamniotic "MoMo"), they also share the same amniotic sac. Monoamniotic twins occur when the split takes place after the ninth day after fertilization.[2] Monoamniotic twins are always monozygotic (identical twins).[3] Monochorionic-Diamniotic twins are almost always monozygotic, with a few exceptions where the blastocysts have fused.[2]
Diagnosis
λ Sign in 8 week pregnancy
By performing an obstetric ultrasound at a gestational age of 10-14 weeks, monochorionic-diamniotic twins are discerned from dichorionic twins. The presence of a "T-sign" at the inter-twin membrane-placental junction is indicative of monochorionic-diamniotic twins (that is, the junction between the inter-twin membrane and the external rim forms a right angle), whereas dichorionic twins present with a "lambda (λ) sign" (that is, the chorion forms a wedge-shaped protrusion into the inter-twin space, creating a rather curved junction).[4] The "lambda sign" is also called the "twin peak sign". At ultrasound at a gestational age of 16-20 weeks, the "lambda sign" is indicative of dichorionicity but its absence does not exclude it.[5]
In contrast, the placentas may be overlapping for dichorionic twins, making it hard to distinguish them, making it difficult to discern mono- or dichorionic twins on solely the appearance of the placentas on ultrasound.
Complications
In addition to a shared placenta, monochorionic twins also have their circulatory systems intermingled in random and unpredictable circulatory anastomoses. This can cause disproportionate blood supply, resulting in twin-to-twin transfusion syndrome (TTTS) in 20%[1] of MoDi pregnancies. This is the main complication of monochorionic twins.
The 80% of MoDi pregnancies without TTTS still have high rates of birth weight discordance, fetal growth restriction, prematurity and resultant cesarean section deliveries.[1] One twin may also fail to develop a proper heart and become dependent on the pumping activity of the other twin's heart, resulting in twin reversed arterial perfusion.[2] If one twin dies in utero, blood accumulates in that twin's body, causing exsanguination of the remaining twin.[2]
In the case of monoamniotic twins the risk of complications is substantially higher because of additional potential umbilical cord entanglement and compression.[3] However, the perinatal mortality of monochorionic twins is fairly low.[1]
See also
- Twin reversed arterial perfusion
References
- ^ a b c d Cordero L, Franco A, Joy SD, O'shaughnessy RW (December 2005). "Monochorionic diamniotic infants without twin-to-twin transfusion syndrome". J Perinatol 25 (12): 753–8. doi:10.1038/sj.jp.7211405. PMID 16281049.
- ^ a b c d e f Shulman, Lee S.; Vugt, John M. G. van (2006). Prenatal medicine. Washington, DC: Taylor & Francis. pp. Page 447. ISBN 0-8247-2844-0.
- ^ a b Pregnancy-Info -- > Monoamniotic Twins Retrieved on July 9, 2009
- ^ Sepulveda, W.; Sebire, N. J.; Hughes, K.; Odibo, A.; Nicolaides, K. H. (1996). "The lambda sign at 10-14 weeks of gestation as a predictor of chorionicity in twin pregnancies". Ultrasound in Obstetrics and Gynecology 7 (6): 421–423. doi:10.1046/j.1469-0705.1996.07060421.x. PMID 8807758. edit
- ^ Sepulveda, W.; Sebire, N.; Hughes, K.; Kalogeropoulos, A.; Nicolaides, K. (1997). "Evolution of the lambda or twin-chorionic peak sign in dichorionic twin pregnancies". Obstetrics & Gynecology 89 (3): 439–441. doi:10.1016/S0029-7844(97)85858-9. PMID 9052601. edit
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Twin conditions (Q89.3–Q89.4, 759.3–759.4)
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| Zygosity |
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| Monochorionic twins |
- Twin-to-twin transfusion syndrome
- Twin reversed arterial perfusion
- Monoamniotic twins
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| Conjoined twins |
- Parasitic twin (Craniopagus parasiticus, Fetus in fetu)
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| Other |
- Vanishing twin
- Chimerism
- Mixed twins
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Pathology of pregnancy, childbirth and the puerperium (O, 630–679)
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| Pregnancy |
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Pregnancy with
abortive outcome
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- Ectopic pregnancy
- Abdominal pregnancy
- Cervical pregnancy
- Interstitial pregnancy
- Ovarian pregnancy
- Molar pregnancy
- Miscarriage
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Oedema, proteinuria and
hypertensive disorders
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- Gestational diabetes
- Gestational hypertension
- Pre-eclampsia
- Eclampsia
- HELLP syndrome
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Other, predominantly
related to pregnancy
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Digestive system
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- Acute fatty liver of pregnancy
- Hepatitis E
- Hyperemesis gravidarum
- Intrahepatic cholestasis of pregnancy
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Integumentary system /
dermatoses of pregnancy
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- Gestational pemphigoid
- Impetigo herpetiformis
- Intrahepatic cholestasis of pregnancy
- Linea nigra
- Prurigo gestationis
- Pruritic folliculitis of pregnancy
- Pruritic urticarial papules and plaques of pregnancy (PUPPP)
- Striae gravidarum
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Nervous system
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Blood
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- Gestational thrombocytopenia
- Pregnancy-induced hypercoagulability
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Maternal care related to the
fetus and amniotic cavity
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- amniotic fluid
- Oligohydramnios
- Polyhydramnios
- Braxton Hicks contractions
- chorion / amnion
- Amniotic band syndrome
- Chorioamnionitis
- Chorionic hematoma
- Monoamniotic twins
- Premature rupture of membranes
- Obstetrical hemorrhage
- placenta
- Circumvallate placenta
- Monochorionic twins
- Placenta praevia
- Placental abruption
- Twin-to-twin transfusion syndrome
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| Labor |
- Amniotic fluid embolism
- Cephalopelvic disproportion
- Dystocia
- Fetal distress
- Locked twins
- Obstetrical hemorrhage
- placenta
- Preterm birth
- Postmature birth
- Umbilical cord prolapse
- Uterine rupture
- Vasa praevia
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| Puerperal |
- Breastfeeding difficulties
- Agalactia
- Fissure of the nipple
- Galactorrhea
- Breast engorgement
- Diastasis symphysis pubis
- Peripartum cardiomyopathy
- Postpartum depression
- Postpartum thyroiditis
- Puerperal fever
- Puerperal mastitis
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| Other |
- Concomitant conditions
- Diabetes mellitus
- Systemic lupus erythematosus
- Thyroid disorders
- Maternal death
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