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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 ...
Monochorionic twins are twins that share the same placenta. This occurs in 0.3% of all pregnancies, [3] and in 75% of monozygotic (identical) twins, when the split takes place on or after the third day after fertilization. [4] The remaining 25% of monozygous twins become dichorionic diamniotic. [4]
Identical twins have identical genomes in the immediate aftermath of twinning. About two-thirds of monozygotic twins share the same placenta, arising by cleavage before the fourth day of development; the other third have separate placentas because cleavage has taken place after the fourth day after choriogenesis has begun.
Monoamniotic twins are always monochorionic and are usually termed Monoamniotic-Monochorionic ("MoMo" or "Mono Mono") twins. [1] [2] They share the placenta, but have two separate umbilical cords. Monoamniotic twins develop when an embryo does not split until after formation of the amniotic sac, [1] at about 9–13 days after fertilization. [3]
In 1982, twins who were born with two different skin colors were discovered to be conceived as a result of heteropaternal superfecundation. [7] [5] In 1995, a young woman gave birth to diamniotic monochorionic twins, who were originally assumed to be monozygotic twins until a paternity suit led to a DNA test. This led to the discovery that the ...
In humans, the circulatory system is different before and after birth. The fetal circulation is composed of the placenta, umbilical blood vessels encapsulated by the umbilical cord, heart and systemic blood vessels. A major difference between the fetal circulation and postnatal circulation is that the lungs are not used during the fetal stage ...
Presentation of twins in Der Rosengarten ("The Rose Garden"), a German standard medical text for midwives published in 1513. In obstetrics, the presentation of a fetus about to be born specifies which anatomical part of the fetus is leading, that is, is closest to the pelvic inlet of the birth canal.
The human reproductive system includes the male reproductive system, which functions to produce and deposit sperm, and the female reproductive system, which functions to produce egg cells and to protect and nourish the fetus until birth. Humans have a high level of sexual differentiation.