About 1 in 33 babies in the United States is born with a birth defect. That translates to roughly 120,000 affected newborns each year, making birth defects far more common than most people realize. They range from mild conditions that need no treatment to serious structural or genetic differences that require lifelong care.
The Most Common Types
Birth defects fall into a few broad categories: structural problems (where a body part forms incorrectly), chromosomal conditions (where there’s an extra or missing piece of genetic material), and functional issues (where a body system doesn’t work properly). Some are visible at birth, while others aren’t discovered until later in childhood or even adulthood.
Heart defects are by far the most common structural birth defect, affecting nearly 1% of all births, or about 40,000 babies per year in the U.S. alone. The most frequent type is a ventricular septal defect, a hole in the wall between the heart’s two lower chambers. Many small holes close on their own during infancy. Larger ones may require surgery, but outcomes have improved dramatically over the past few decades.
Down syndrome is the most common chromosomal condition, occurring in about 1 in every 640 births. That works out to roughly 5,700 babies per year in the U.S. Neural tube defects, which include spina bifida and anencephaly, are less common but among the most serious structural defects. Spina bifida occurs at a rate of about 2.7 to 3.8 per 10,000 live births depending on racial and ethnic background, with Hispanic populations having the highest rates.
Fetal alcohol spectrum disorders are a significant but often overlooked category. An estimated 1 to 5 percent of U.S. first graders are affected, a range that reflects how difficult these conditions are to diagnose and how widely alcohol use during pregnancy varies across populations.
What Raises the Risk
Most birth defects result from a combination of genetic and environmental factors, and for many, no single cause can be identified. That said, several well-established risk factors shift the odds.
Maternal age is one of the strongest predictors for chromosomal conditions. A woman who conceives at age 25 has roughly a 1 in 1,250 chance of having a baby with Down syndrome. By age 40, that risk jumps to about 1 in 100. Age 35 is generally considered the threshold for “advanced maternal age,” but the risk increases on a continuum rather than at a single cutoff.
Exposures during pregnancy also matter. Alcohol use can cause fetal alcohol spectrum disorders. Poorly controlled diabetes, certain medications, and infections like rubella or Zika virus during pregnancy are all linked to higher rates of specific defects. Folic acid deficiency before and during early pregnancy is strongly connected to neural tube defects, which is why fortified foods and prenatal vitamins emphasize this nutrient.
How Many Are Caught Before Birth
Prenatal screening catches many, but not all, birth defects. The standard anatomy ultrasound performed around 20 weeks of pregnancy is designed to look for major structural problems. Research on its accuracy shows an overall detection rate of about 75% for major anomalies. That means roughly one in four significant defects is missed on ultrasound, sometimes not identified until later in pregnancy or after delivery.
Timing also plays a role. Among defects that are eventually spotted on ultrasound, only about 28% are detected by 22 weeks of pregnancy, the point at which many clinical decisions are made. Blood tests and genetic screening can identify chromosomal conditions like Down syndrome with high accuracy, but these are separate from the ultrasound and are typically offered based on age, family history, or initial screening results.
Global Differences in Prevalence
Birth defects are not evenly distributed around the world. A 2021 global analysis found that prevalence was highest in low-income regions, at about 1,693 per 100,000 children, compared to roughly 1,521 per 100,000 in high-income regions. The correlation between a country’s development level and its birth defect rate is strong: as socioeconomic development increases, prevalence drops. This gap reflects differences in nutrition (particularly folic acid intake), access to prenatal care, environmental exposures, and rates of consanguinity in some populations.
The Toll on Families and the Healthcare System
Birth defects accounted for 20.6% of all infant deaths in the United States in 2017, making them the leading cause of infant mortality. Many children who survive require repeated hospitalizations, surgeries, therapies, and specialized care throughout childhood and beyond.
The financial burden is substantial. In 2019, hospitalizations associated with birth defects cost an estimated $22.2 billion in the U.S. for patients under 65. That represented just 4.1% of all hospitalizations in that age group but accounted for 7.7% of total hospitalization costs, reflecting how complex and resource-intensive these conditions are to treat. These figures capture only inpatient hospital costs and don’t include outpatient visits, therapies, medications, or the economic impact on families who reduce work hours to provide care.