baby holding a finger tightly
11 March 2015

How Common Are Birth Defects?

Over 4 million babies are born to American mothers every year. We wanted to know how many of these children are born with birth defects, so we dove into a wealth of resources to find the answer.

Birth Defects: Facts & Statistics baby holding a finger tightly

According to the US Centers for Disease Control & Prevention (CDC), about 3% of all babies (or one out of 33) are born with some type of birth defect.

Assuming 4 million total births, 3% represents 120,000 babies.

The CDC also provides estimates for specific types of birth defect, although their numbers are only current as of 2006. Here are the most common:

  1. Congenital heart defects (40,000 babies every year)
  2. Orofacial defects, like cleft lip and cleft palate (6,776 babies every year)
  3. Down syndrome (6,037 babies every year)
  4. Musculoskeletal defects (5,799 babies every year)
  5. Gastrointestinal defects (2,883 babies every year)
  6. Spina bifida (1,460 babies every year)

Birth defects are a leading cause of death, and contribute to around 20% of all infant deaths. Unfortunately, many states do a poor job of tracking congenital abnormalities, so the CDC’s estimates are only based on birth records from 11 states.

Cleft Lip & Palate

Orofacial defects, like cleft palate and cleft lip, are relatively common. But these conditions come in several forms:

  • Around 1 in every 1,574 babies are born with cleft palate, without cleft lip
  • Around 1 in every 940 babies are born with cleft lip, with or without cleft palate

While orofacial clefts can be associated with several genetic disorders, anywhere from 50% to 80% of all babies born with cleft palate and / or cleft lip have no other syndrome.

The CDC reports that women with diabetes, along with those who take certain medications (especially drugs for epilepsy) or smoke during pregnancy, are at an increased risk of having a baby with an orofacial cleft.

Congenital Heart Defects

Ventricular septal defects, in which a barrier between chambers of the heart fails to close completely, are the most common form of congenital heart defect (CHD).

Like orofacial clefts, some CHDs are accompanied by a genetic condition. But about 85% of the babies born with a CHD have no genetic syndrome.

In about 1 out of 4 babies born with a congenital heart defect, the condition is critical and requires surgery within the first year of life.

What Causes Birth Defects?

In most cases, the specific cause of a birth defect will never be discovered. With that being said, researchers agree that congenital anomalies can be explained through reference to two factors:

Genetic material

Genes are the very stuff of life. Inherited from both parents, genetic material dictates all the “action” going on during fetal development.

Genes tell cells to make proteins that will eventually combine to form organs, direct cells to move and control almost every process essential to the creation of an organism.

When some of this genetic information is missing or duplicated erroneously, cells are instructed to do things they normally wouldn’t, including form what we call “birth defects.”

Environmental factors

When ingested by an expectant mother, certain medications, along with voluntary habits like smoking and drinking alcohol, can disrupt the normal development of a baby.

Many chemicals pass through the “placental barrier,” flowing through a mother’s blood stream and into her growing baby. Some seem to inhibit the activities of genes, although researchers are still in the dark as to exactly why.

How Many Women Take Prescription Drugs During Pregnancy?

Around half.

In a study performed by Boston University’s Slone Epidemiology Center, researchers found that:

  • out of more than 30,000 women, around 50% reported taking at least one prescription drug during the first trimester of pregnancy.
  • Since 1976, “first-trimester use of prescription medication [has] increased by more than 60%.”

That’s not necessarily cause for concern. Many medications are perfectly safe, even for developing babies. But in the next section, we’ll discuss prescriptions that may be dangerous, and try to discover how often those drugs are taken by pregnant women.

Do We Know How Many Women Take Dangerous Drugs During Pregnancy?

In a study led by researchers at the University of Ottawa, a total of 18,575 women who gave birth between 1997 and 2000 were studied.

Out of nearly 20,000 pregnant women, almost 20% had been prescribed drugs categorized as either Pregnancy Category C, D or X:

  • 15.8% took drugs in Category C
  • 5.2% took drugs in Category D
  • 3.9% took drugs in Category X

Researchers at Harvard and the University of Massachusetts performed a similar review, this time using health records in America. They identified a total of 152,531 pregnancies that occurred between 1996 and 2000:

  • 64% of the women took a prescription drug during pregnancy
  • 37.8% received a drug in Category C
  • 4.8% received a drug in Category D
  • 4.6% received a drug in Category X

That’s 47.2% out of 152,531 women who took drugs in Categories C, D or X. The proportion of US women prescribed medications that may be unsafe was more than twice that in Canada.

In the next section, we’ll discuss what the FDA’s pregnancy categories mean, and how difficult it is to know whether or not a drug is dangerous for pregnant women and their developing babies.

What Do Pregnancy Categories Mean?

Although the FDA has recently changed the way in which pregnancy risks are listed on warning labels, the alphabetical “Pregnancy Category” system ranked medications in one of 5 categories based on clinical evidence:

  • Drugs were listed in Category C because “animal reproduction studies ha[d] shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.”
  • Drugs were listed in Category D because “there is positive evidence of human fetal risk based on adverse reaction data[,] but potential benefits may warrant use of the drug in pregnant women despite potential risks.”
  • Drugs were listed in Category X because “studies in animals or humans have demonstrated fetal abnormalities and / or there is positive evidence of human fetal risk[,] and the risks involved in use of the drug in pregnant women clearly outweigh potential benefits.”

In simplified terms:

  • Category C means: “this drug harms fetuses in pregnant animals, but we don’t know what it does in humans.”
  • Category D means: “after pregnant women started taking this drug, we received reports of fetal harm. There may be an association, but we’re not sure.”
  • Category X means: “We know that this drug is dangerous for pregnant humans, and women should not take it.”

Are All Those Drugs Dangerous?

Not necessarily.

Testing the effects of a drug on pregnant women is generally seen as unethical. For that reason, it’s rare that the health community becomes aware of a medication’s potential to cause fetal harm before actual harm is done. We just don’t have the research that would allow us to know whether or not a drug is safe until pregnant women take it.

In most cases, we only have studies in pregnant animals. But the results of animal studies are never assumed to imply similar results in humans. In other words, even though we may know that a drug has damaging effects on fetal development in animals, doctors can still prescribe it to pregnant women. But only if they believe that the drug’s potential benefits outweigh its potential risks.

In medicine, this is the law of the land. Everything is a benefit to risk evaluation. Only drugs in Category X are universally seen as a bad idea during pregnancy.

Even so, the Canadian researchers found that 3.9% of the pregnant women in their study had been prescribed drugs in Category X. That’s 724 women prescribed medications with risks that the FDA believes “clearly outweigh the potential benefits.”

The researchers from Harvard found an even higher proportion: 4.6% of 98,182 women had received a medication in Category X. That’s about 4,516 women over the course of four years.

Again, not all of those developing babies were being harmed by the drugs their mothers took. And we’re sure their doctors acted ethically, weighing benefits against potential risks and coming to a reasoned decision. But the point is that we don’t know.