Suggested Reading

Amselem S, et al.: Laron dwarfism and mutations in the growth hormone receptor gene. N Engl J Med 321:989, 1989.

Barnea ER, Hustin J, Jauniaux E (eds): The First Twelve Weeks of Gestation. Berlin, Springer-Verlag, 1992.

Bassett JM: Current perspectives on placental development and its integration with fetal growth.

ProcNutrSoc 50:311, 1991. Benirschke K, Kaufman P: The Pathology of the Human Placenta. Berlin, Springer-Verlag, 1990. Cunningham FG, Gant NF, Leveno KJ, Gilstrap LC, Hauth JC, Wenstrom KD: Fetal growth and development. In Williams Obstetrics. New York, McGraw Hill, 2001. Cunningham FG, Gant NF, Leveno KJ, Gilstrap LC, Hauth JC, Wenstrom KD: Parturition. In Williams

Obstetrics. New York, McGraw Hill, 2001. Levi S: Ultrasonic assessment of the high rate of human multiple pregnancy in the first trimester.

J Clin Ultrasound 4:3, 1976. Naeye RL: Disorders of the Placenta, Fetus, and Neonate. St Louis, Mosby-Year Book, 1992.

Nyberg DA, Callan PW: Ultrasound evaluation of the placenta. In Callen PW (ed): Ultrasonography in Obstetrics and Gynecology. 2nd ed. Philadelphia, WB Saunders, 1988. PeipertJF, Donnenfeld AE: Oligohydramnios: a review. Obstet Gynecol 46:325, 1991. Petraglia F, et al.: Neuroendocrine mechanisms regulating placental hormone production. Contrib

Gynecol Obstet 18:147, 1991. Schnaufer L: Conjoined twins. In Raffensperger JG (ed): Swenson's Pediatric Surgery. 5th ed.

Norwalk, CT, Appleton & Lange, 1990. Spencer R: Conjoined twins: theoretical embryologic basis. Teratology 45:591, 1992. Wallace I, Wallace A: The Two. New York, Simon and Schuster, 1978.

Wilcox AJ, Weinberg CR, Baird DD: Timing of sexual intercourse in relation to ovulation. N Engl J Med 333:1517, 1995.

Congenital Anomalies Infants

Birth Defects chapter 7

Birth Defects and Prenatal Diagnosis

Birth Defects

Birth defect, congenital malformation, and congenital anomaly are synonymous terms used to describe structural, behavioral, functional, and metabolic disorders present at birth. The science that studies these disorders is teratology (Gr. teratos, monster). Major structural anomalies occur in 2 to 3% of liveborn infants, and an additional 2 to 3% are recognized in children by age 5 years, for a total of 4 to 6%. Birth defects are the leading cause of infant mortality, accounting for approximately 21% of infant deaths. They are the fifth leading cause of years of potential life lost prior to age 65 and a major contributor to disabilities. They are also nondiscrimina-tory; mortality rates produced by birth defects are the same for Asians, African Americans, Latin Americans, whites, and Native Americans.

In 40 to 60% of persons with birth defects, the cause is unknown. Genetic factors, such as chromosome abnormalities and mutant genes, account for approximately 15%; environmental factors produce approximately 10%; a combination of genetic and environmental influences (multifactorial inheritance) produces 20 to 25%; and twinning causes 0.5 to 1%.

Minor anomalies occur in approximately 15% of newborns. These structural abnormalities, such as microtia (small ears), pigmented spots, and short palpebral fissures, are not themselves detrimental to health but, in some cases, are associated with major defects. For example, infants with one minor anomaly have a 3% chance of having a major malformation; those with two minor anomalies have a 10% chance; and those with three or more minor anomalies have a 20% chance. Therefore, minor anomalies serve as clues for diagnosing more serious underlying defects. In particular, ear anomalies are easily recognizable indicators of other defects and are observed in virtually all children with syndromic malformations.

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