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Defects originate from two primary sources: genetic inheritance and environmental exposure. Both can manifest at birth, with the fetal period being particularly vulnerable to environmental insults. During gestation, a child’s genome, shaped by parental DNA, may reveal inherited anomalies, while exposure to harmful agents can also trigger defects.
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Genes—encoded in deoxyribonucleic acid (DNA) and organized on chromosomes—constitute the units of heredity. Each child inherits one copy of every gene from each parent, requiring two functional copies for normal development. Inherited defects can stem from gene mutations, chromosomal number or structure abnormalities, and complex gene‑gene or gene‑environment interactions, such as those influenced by nutrition.
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Pregnancy carries a developing child from fertilization to birth. During this window, infections by bacteria, viruses, fungi, and protozoans can cause birth defects. Maternal rubella infection, for example, can result in ocular, auditory, and cardiac anomalies in the newborn. Toxoplasmosis, transmitted via undercooked meat or contaminated soil, may lead to severe malformations.
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Environmental toxins are frequent culprits of birth defects. The sedative thalidomide, used in the 1950s and 60s to alleviate morning sickness, is now linked to phocomelia—a limb‑shortening disorder. Fetal alcohol syndrome, caused by excessive maternal alcohol consumption, results in cognitive deficits and growth restriction. Maternal smoking exposes the fetus to harmful chemicals, often leading to low birth weight and increased defect risk.
Radiation can damage DNA, and the developing fetus is especially susceptible. Heat exposure has been associated with a rare form of fetal blindness. Adequate maternal nutrition is crucial; deficiencies in B‑vitamins may cause spinal, brain, and cardiac anomalies.
