A congenital anomaly is any structural or functional abnormality that develops before birth. These conditions, also called birth defects or congenital disorders, affect roughly 3% to 6% of infants born worldwide each year. Some are visible immediately, like a cleft lip. Others, such as a heart defect or a metabolic disorder, may not be discovered until weeks, months, or even years later.
Types of Congenital Anomalies
Congenital anomalies fall into three broad categories. External structural defects are those you can see on the body’s surface, such as cleft lip, clubfoot, or an abdominal wall that didn’t fully close during development. Internal structural defects involve organs that formed incorrectly, with heart defects being the most common example. Functional defects affect how the body processes substances or carries out normal biological tasks, even though the organs may look normal. Inherited metabolic conditions where the body can’t break down certain sugars or fats are examples of functional anomalies.
A baby can have a single isolated defect or multiple anomalies that occur together. Some clusters of defects form recognizable patterns linked to a specific genetic cause, like the set of heart, facial, and developmental features seen in Down syndrome.
What Causes Congenital Anomalies
The causes break down into three groups: genetic, environmental, and a combination of both. In many cases, no single cause can be identified.
On the genetic side, chromosomal abnormalities (having extra, missing, or rearranged chromosomes) account for a significant share. Single gene mutations also play a role. Researchers have identified specific genes linked to heart defects, cleft palate, and other conditions.
Environmental factors that can disrupt fetal development are called teratogens. The list is long and well documented:
- Alcohol can cause a range of physical and cognitive effects grouped under fetal alcohol spectrum disorders.
- Certain medications carry serious risks. Valproate, used for epilepsy and mood disorders, is linked to spinal cord defects, heart anomalies, and developmental delays. The blood thinner warfarin can cause skeletal abnormalities. The antibiotic streptomycin has been shown to cause irreversible bilateral deafness when used in the first trimester.
- Maternal infections during pregnancy, including rubella, Zika virus, and cytomegalovirus, can interfere with organ development.
- Maternal health conditions like pre-existing or gestational diabetes and obesity increase risk.
- Environmental exposures such as air pollution, toxic chemicals, and parental smoking are also associated with higher rates of birth defects.
Global Impact
In 2021, there were an estimated 7.2 million cases of congenital birth defects and 530,000 associated deaths worldwide. Congenital disorders now rank as the third leading cause of death among people under 20. An estimated 240,000 newborns die within their first 28 days of life due to these conditions each year, with another 170,000 children dying between one month and five years of age.
The burden is not evenly distributed. About 94% of severe congenital disorders occur in low- and middle-income countries, where access to surgical care, diagnostic tools, and specialized treatment is limited. As infectious disease prevention has improved globally, reducing overall childhood mortality by 52% since 1990, congenital anomalies have grown as a proportion of the deaths that remain.
How They’re Detected Before Birth
Prenatal screening can identify many congenital anomalies well before delivery. The timeline typically follows a two-stage process across pregnancy.
First-trimester screening happens between 10 and 14 weeks. It combines an ultrasound measurement of fluid at the back of the baby’s neck (a marker for chromosomal conditions like Down syndrome) with a blood test measuring specific proteins. Cell-free DNA testing, which analyzes tiny fragments of fetal DNA circulating in the mother’s blood, can also be performed from 10 weeks onward and screens for several chromosomal conditions with high accuracy.
Second-trimester screening, done between 15 and 22 weeks, involves blood tests that measure a panel of hormones and proteins. These are sometimes called the triple or quadruple screen depending on how many markers are tested. All patients are also offered a detailed anatomy ultrasound between 18 and 22 weeks, which examines the baby’s organs, limbs, spine, and brain for structural abnormalities.
These are screening tests, meaning they estimate risk rather than give a definitive answer. If screening results suggest a higher chance of an anomaly, diagnostic procedures like amniocentesis can confirm or rule out the condition.
Treatment and Long-Term Outlook
Treatment depends entirely on the type and severity of the anomaly. Many structural defects can be surgically corrected, sometimes in a single procedure and sometimes through staged repairs over months or years. Heart defects, abdominal wall defects, and intestinal abnormalities often require surgery in the first days or weeks of life.
Not all treatment is surgical. Clubfoot, for example, is treated with a series of casts that gradually reposition the foot, a technique successful in up to 98% of patients. After casting, a small procedure to release the Achilles tendon is common, followed by corrective braces worn for several years to prevent relapse.
For abdominal wall defects like gastroschisis, where the intestines develop outside the body, babies need careful management of heat loss and fluid balance after birth. Once these infants survive the newborn period, they typically have little to no long-term disability. Functional anomalies like metabolic disorders generally require lifelong management through diet, enzyme replacement, or other medical therapies rather than surgery.
Access to care is a critical factor in outcomes. In higher-income countries, many congenital anomalies that once were fatal are now treatable with good long-term results. In lower-income settings, even straightforward surgical conditions can become life-threatening when specialist care isn’t available.
Prevention
Some congenital anomalies can’t be prevented, particularly those caused by random genetic changes. But a meaningful number can be reduced through specific measures before and during pregnancy.
Folic acid is the most well-established preventive tool. Taking 400 micrograms daily before conception and during early pregnancy significantly reduces the risk of neural tube defects like spina bifida. The key detail: folic acid needs to be on board before pregnancy begins, because the neural tube forms in the first few weeks, often before a person knows they’re pregnant. Women who have previously had a pregnancy affected by a neural tube defect are advised to take a much higher dose of 4,000 micrograms daily, starting at least one month before conception.
Vaccination against rubella before pregnancy eliminates one of the known infectious causes. Managing diabetes before conception, avoiding alcohol, and reviewing all medications with a healthcare provider to identify potential teratogens are all practical steps that lower risk. Reducing exposure to environmental toxins and secondhand smoke adds another layer of protection.