Congenital disorders and the fetus
- Congenital anomalies refer to structural defects present at birth. Major congenital anomalies (those incompatible with life or requiring major surgery) occur in 2–3% of live births, and 5% have minor malformations.
- Of congenital anomalies 30–40% have a known cause, including chromosomal abnormalities (0.5% of live births), single gene defects (1% of births), multifactorial disorders, and teratogenic exposures; 60–70% have no known cause.
Classification of chromosomal abnormalities
Autosomal disorders
- Trisomy 21 (Down syndrome). The most common autosomal disorder. Overall incidence is 1/800 live births, but it is strongly associated with maternal age (Figure 39.1). Long-term prognosis depends largely on the presence of cardiac anomalies.
- Trisomy 18 (Edward syndrome). One in 3,500 births. It is characterized by intrauterine growth restriction (IUGR), single umbilical artery, overlapping clenched fingers, and “rocker-bottom” feet. Fewer than 10% of infants survive to age 1.
- Trisomy 13 (Patau syndrome). One in 5,000 births. IUGR with facial clefts, ocular anomalies, and polydactyly. Fewer than 3% survive to age 3.
- 5p- (cri-du-chat syndrome). One in 20,000 births. Round facies, epicanthal folds, learning disability, and a high-pitched, monotonous cry. Variable survival.
Sex chromosomal disorders
- 47,XXY (Klinefelter syndrome). The most common sex chromosome disorder; 1/500 births. Male phenotype, but with female adipose distribution and breast development. Normal pubic and axillary hair, scant facial hair. Twentyfold increase in breast cancer. Usually infertile.
- 45,X (Turner syndrome). One in 2,500 live births (but accounts for around 25% of early miscarriage). Short female with a webbed neck, primary amenorrhea, renal anomalies, cardiac defect (aortic coarctation). Affected individuals are infertile.
- 47,XYY. One in 800 births. Tall male with normal genitalia and testosterone levels, but intellectually limited. Usually fertile.
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