Most people carry a minor birth anomaly without ever knowing it
A curved little finger, a tiny pit near the ear, a dimple at the base of the spine: careful examination finds at least one minor anomaly in many, perhaps most, people. Birth defects in the serious sense affect about 3% of US newborns, and their global death toll has fallen since 1990.
A birth defect is any abnormal condition present at birth, whatever its cause. Doctors split them into structural problems, where a body part is shaped differently, and functional ones, where it works differently, a group that includes metabolic and degenerative disorders. Some involve both. Terminology also distinguishes how things go wrong: malformations arise from faulty tissue development, often in the first trimester, while deformations come from mechanical pressure on normal tissue later in pregnancy, sometimes linked to low amniotic fluid.
Around 96 million people were living with a birth defect in 2015. Deaths attributed to them fell from 751,000 in 1990 to about 628,000 in 2015, with congenital heart disease the largest killer at 303,000 and neural tube defects, such as spina bifida, next. Cleft palate offers a clear example of timing: it forms between the fourth and seventh weeks of gestation, when tissue growing in from each side of the head fails to join.
Causes range from genetic and chromosomal disorders to infections, drugs and chemicals, and the CDC notes that many defects have no known cause. Recognised risk factors include low folate, alcohol or smoking in pregnancy, poorly controlled diabetes and a mother over 35. Substances that cause such harm are called teratogens, and an estimated 10% of birth defects stem from them, making those cases potentially preventable. No safe level of alcohol in pregnancy is known.
The most notorious teratogen is thalidomide, developed by Chemie Grünenthal in the late 1950s as a sleeping aid and anti-nausea drug and given to pregnant women in almost 50 countries. Before William McBride's study prompted its withdrawal in 1961, roughly 8,000 to 10,000 severely affected children were born. Animal research has also linked fathers' alcohol use to lower birth weight in offspring.
Source: Birth defect
