CYTOGENETIC DISORDERS
At least 50% of first-trimester abortuses have abnormal chromosomes. The
2 most common aneuploidies in miscarriage are trisomy 16 and monosomy X
(50% of these abnormalities are autosomal trisomies, with trisomy 16 the most
common).
Turner syndrome (45,X) (also known as gonadal dysgenesis or monosomy
X) (1 in 2,000 births) is most often the result of loss of the paternal X
chromosome; 98% of these conceptions abort spontaneously. Obstetric
ultrasound shows the characteristic nuchal skin-fold thickening and cystic
hygroma. Those fetuses that do survive to term have the following:
Absence of secondary sexual development
Short stature
Streak gonads
Primary amenorrhea/primary infertility
Broad chest
Neck webbing
Urinary tract anomalies
Bicuspid aortic valve and aortic coarctation
Normal intelligence
Possible mosaic patterns, with ovarian follicles present
Klinefelter syndrome (47,XXY) (1 in 1,000 births) is seldom diagnosed
before puberty. Physical findings include tall stature, testicular atrophy,
azoospermia, gynecomastia, and truncal obesity. Learning disorders,
autoimmune diseases, and low IQ are common.
Down syndrome (trisomy 21) (1 in 800 births) accounts for 50% of all
cytogenetic diseases at term. IUGR and polyhydramnios are common. T21
incidence increases with advancing maternal age. The syndrome is
characterized by intellectual disability, short stature, muscular hypotonia,
brachycephaly, and short neck. Typical facial appearance is oblique orbital
fissures, flat nasal bridge, small ears, nystagmus, and protruding tongue.
Congenital heart disease (endocardial cushion defects) is more common
along with duodenal atresia