Abstract The term monochorionic refers to a multiple gestation with one placental disk (or chorion), whereas monoamniotic describes the presence of only one amniotic cavity. By definition, monoamniotic twin pregnancies…
Abstract Chorionicity refers to the number of placentas in a multiple gestation; amnionicity refers to the number of amniotic cavities. Prenatal determination of chorionicity and amnionicity is essential in the…
Abstract Miller-Dieker syndrome, or 17p13.3 deletion syndrome, is a rare, contiguous gene deletion syndrome characterized by type 1 lissencephaly, facial dysmorphism, seizures, and severe mental retardation. Impaired neuronal migration between…
Abstract The 22q11.2 deletion syndrome is the most common human chromosomal microdeletion syndrome and one of the most common genetic syndromes associated with prenatally detected congenital heart defects (CHDs). It…
Abstract Turner syndrome (monosomy X) is characterized by the complete or partial loss of the second X chromosome in the female, with or without cell line mosaicism. There are three…
Abstract The most severe trisomies usually result in early pregnancy loss. However, some of these severe trisomies may survive to birth if they are mosaics, in which the condition only…
Abstract Sirenomelia is characterized by a single lower limb, bilateral renal agenesis, and single umbilical artery contiguous with the aorta. Internal and/or external genitalia anomalies as well as oligo/anhydramnios may…
Abstract Trisomy 21 (Down syndrome) is the most common autosomal trisomy in newborns, and is strongly associated with increasing maternal age. Trisomy 21 results most commonly from maternal meiotic nondisjunction….
Abstract Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder caused by mutations in the gene encoding the 7-dehydrocholesterol reductase (7-DHC) resulting in decreased or absent function of this enzyme responsible…
Abstract Trisomy 18 (Edwards syndrome) is the second most common autosomal trisomy in newborns. More than 90% of cases are the result of maternal nondisjunction of chromosome 18. Fetuses with…
