MONOZYGOTIC (IDENTICAL) TWINS

MONOZYGOTIC (IDENTICAL) TWINS Occasionally  a single fertilized egg forms a zygote that divides to form two separate embryos during the first 2 weeks after conception. These twins are referred to as monozygoticor "identical" twins. Depending on the timing of the division each zygote may develop its own membranes and placenta or the embryos may share the membrane and placenta. If the division occurs very late the twins will be conjoined.
PLACENTAL TYPES Dichorionic (two placentas), Diamniotic (two amnions) ( 18 to 36 % of monozygotic twins )  If a single zygote divides into two separate embryos within 72 hours after fertilization then the twins will develop in two separate amniotic sacs (bag of water) and will have their own, separate, placentas. However, the placentas may at times appear to be fused [25]..
LifeART image copyright 2005 Lippincott Williams & Wilkins. All rights reserved.
Monochorionic (one placenta), Diamniotic (two amnions) ( 60 to 70 % of monozygotic twins ) If division occurs 3 to 8 days after fertilization then the twins will develop in two separate amniotic sacs (bag of water) and will share one placenta [25].	LifeART image copyright 2005 Lippincott Williams & Wilkins. All rights reserved.
Monochorionic (one placenta), Monoamniotic (one amnion) ( 1 to 2 % of monozygotic twins ) If division occurs 8 to 12 days after fertilization then the twins will share one amniotic sac (bag of water) and will share one placenta [25].	LifeART image copyright 2005 Lippincott Williams & Wilkins. All rights reserved.
Monochorionic (one placenta), Monoamniotic (one amnion) ( 0.5 % of monozygotic twins ) If division occurs 12 to 13 days after fertilization then thetwins will share one amniotic sac (bag of water) and will share one placenta. They will also share body parts [25]. Conjoined twins occur 1 in 40,000 total births.	LifeART image copyright 2005 Lippincott Williams & Wilkins. All rights reserved.
ULTRASOUND FINDINGS It is not uncommon to "miss" a monochorionic twin on  ultrasound examination and diagnose these pregnancies as a singleton early [26]. Ultrasound findings which support the diagnosis of monozygotic  twins include [11,12]: Single placental site Same-sex fetuses Thin dividing membrane (two layers or <2 mm) A "T" sign [27] or "empty" lambda sign No chorion extending between the membranes .
FACTORS INFLUENCING THE OCCURRENCE OF MONOZYGOTIC TWINS The birth rate of monozygotic twins worldwide appears to be  relatively constant at 3 to 5 per 1000 births [1]. Infertility therapy Monozygotic twinning has been reported to increase after ovulation induction techniques and in proportion to the number of blastocysts transferred during in vitro fertilisation [28-30]   Maternal or paternal history of monozygotic twinning   Monozygotic twinning transmitted either through the father or mother has been reported [31].

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<--Pregnancy Term Keywords --> Pregnancy Abdomen,The Belly,Abdominal circumference (AC),Abortion,Abruptio placenta (Placental abruption),Acceleration,Acromelia,Active Labor,Acute Cervical Insufficiency,Afterbirth,Agenesis of the corpus callosum (ACC),Akinesia,Alloimmunization (Isoimmunization),Alpha-fetoprotein (AFP),Amniocentesis,Amnioinfusion,Amniotic fluid,Amniotic Fluid Index (AFI),Amniotic fluid ‘sludge’,Amniotic sac,Amniotic sheet,Amniotomy (artificial rupture of membranes , AROM),pregnancy terms,

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