What Are the Most Common Birth Defects?

As much as you’d like a pregnancy to go as smoothly as possible, the reality is conceiving a child is a complex process. One small error, such as a single gene mutation, an extra chromosome or a structure forming abnormally, can lead to a complicated – at least initially – and expensive life for you and your child. 

These malformations, known as birth defects, affect more than 100,000 babies each year. Finding out about a birth defect can be devastating news, but knowledge is power, so we put together a list of the most common birth defects to be familiar with and what causes them.

What is a birth defect?

Birth defects, also called congenital disorders or congenital malformations, are abnormal changes that occur during a pregnancy and are present at birth. Birth defects affect one in every 33 babies (3 percent of all babies) born in the United States each year, according to the CDC.

In general, birth defects can be categorized as structural, genetic or chromosomal. Birth defects that stem from genetic or chromosomal changes are typically thought of as developmental since they may not affect children until their infant years. Developmental birth defects can impact how your child walks, talks, learns, thinks or how the body functions.

Most birth defects occur during the first trimester, typically during the second and third months (weeks 5 through 12) as this is when most of a baby’s structural development occurs. 

In the second month of a pregnancy, arms, legs, fingers, eyes and ears form. Any limb-related birth defects happen at this point. Likewise, the brain and spinal cord finish forming earlier in the second month (week 6), which is when a neural tube defect such as spina bifida would occur. A baby’s heart begins to develop at conception, but it should be fully formed at the eight-week mark. This is when congenital heart defects develop.

As the first trimester comes to a close, reproductive organs begin to develop. This is when a birth defect to the penis, such as hypospadias, would occur.

10 most common birth defects

There are thousands of different birth defects. The most common defects include heart defects, cleft lip and palate and Down syndrome. Here is a list of the top 10 most common birth defects, according to CDC statistics.

Congenital heart defects (CHD) 

Occurrence rate: 1 in every 110 births

Overview: A heart defect is an umbrella term to describe any structural heart issue that affects how the organ works. Some defects impact how blood flows due to holes in the heart while others are more specific to parts of the heart, such as the aorta. 

Hypospadias 

Occurrence rate: 1 in every 200 births

Overview: This male defect occurs when the opening of the urethra is located on the underside of the penis instead of at the tip. This causes difficulty urinating, and surgery is often required.

Ventricular septal defect 

Occurrence rate: 1 in every 240 births

Overview: Known as a hole in the heart, ventricular septal defects are the most common heart defect. The defect occurs when the wall between the left and right ventricle (lower chambers) doesn’t form properly and leaves an opening between the two. Some VSDs get smaller or close on their own while larger holes require surgery.

Clubfoot 

Occurrence rate: 1 in every 593 births

Overview: Clubfoot is a foot abnormality in which the foot turns inward. It is the most common musculoskeletal birth defect. In utero, tendons that connect muscle to bone are shorter, causing the foot to turn inward instead of facing flat. Clubfoot can generally be treated conservatively through gentle stretching and physical therapy. In some cases, clubfoot requires bracing and eventual surgery to adjust the tendons, ligaments and joints of the foot and ankle.

Down syndrome 

Occurrence rate: 1 in every 700 births

Overview: The most common type of chromosomal abnormality, Down syndrome, also called Trisomy 21, occurs when there is an extra copy of chromosome 21. The extra chromosome can cause physical deformities and developmental challenges.

Pulmonary valve atresia and stenosis 

Occurrence rate: 1 in every 1,052 births

Overview: When the heart develops, the pulmonary value either doesn’t exist (pulmonary valve atresia) or the value becomes too thick or is fused and can’t open properly (pulmonary stenosis). As a result, blood doesn’t flow to the lungs correctly. This condition can be treated with medicines, heart catheterization or heart surgery.

Cleft lip with cleft palate 

Occurrence rate: 1 in every 1,563 births

Overview: A type of orofacial cleft, this birth defect occurs when both the lip doesn’t join completely (cleft lip) and the roof of the mouth doesn’t join completely (cleft palate). Surgery during the first 12 to 18 months of your child’s life can correct the issues.

Cleft palate 

Occurrence rate: 1 in every 1,687 births

Overview: This type of birth defect occurs when just the lip doesn’t join completely in utero. Depending on the severity, the opening can be small or large enough to extend into the nose.

Atrioventricular septal defect 

Occurrence rate: 1 in every 1,859 births

Overview: This common type of heart defect occurs when there is both a hole in the heart and a problem with heart valves. A partial defect involves a hole between the atria (upper heart  chambers) and an abnormal mitral valve. A complete defect involves a large hole where the atria and ventricles meet and an abnormal valve between the atria and ventricles instead of having separate valves. Newborns with a partial or complete defect require heart surgery.

Limb defects

Occurrence rate: 1 in every 1,943 births

Overview: The second most common type of musculoskeletal defect behind a clubfoot, this defect describes any abnormality to the arms or legs. Treatment for limb deformities range from physical therapy and bracing to surgery and prosthetics.

What causes birth defects?

Between hundreds of possible gene abnormalities mixed with behavioral and environmental factors, it’s often hard to understand why certain birth defects occur.

Sometimes, a birth defect can be as straightforward as an abnormal gene or chromosome passed down from parent to child. For example, if both parents have a defective copy of the gene that leads to cystic fibrosis, there is a 25 percent chance their child will develop cystic fibrosis.

For other birth defects, the causes are more complex and some are even unknown. In some cases, birth defects are a combination of many factors, such as genetic and behavioral. 

Medical researchers do have a better understanding of some controllable factors that increase your risk of birth defects. Examples include smoking or drinking during pregnancy, exposure to chemicals during pregnancy, taking certain types of medications during pregnancy and certain viral infections (such as Zika virus). A folate deficiency increases your risk of spina bifida and other neural tube defects, which reinforces the importance of taking prenatal vitamins with folic acid.

Age and pre-existing medical conditions also play a role. People with diabetes or obesity and older women are more likely to have children with birth defects.

How are birth defects diagnosed?

Structural birth defects are present at birth and can be diagnosed prenatally with imaging. Genetic and chromosomal birth defects may not be diagnosed until later on in childhood when development milestones aren’t met.

Prenatal ultrasounds

The first chance to screen for birth defects comes around the three-month mark of a pregnancy (11 to 14 weeks) via a nuchal translucency scan. This scan uses ultrasound technology to look for any abnormalities with the nuchal fold thickness, an area of tissue at the back of the fetus’ neck. 

If excess fluid is found, your child is at a higher risk of chromosomal birth defects such as Down syndrome. A nuchal translucency scan isn’t diagnostic, meaning it won’t determine if your child has Down syndrome or another defect. Instead, it means there’s a greater chance of a chromosomal abnormality. 

Once a pregnancy reaches the 20-week stage, your OBGYN will conduct an anatomy scan, sometimes called a Level 2 ultrasound. This comprehensive scan checks for growth, limb and organ development, breathing and movement. Based on the findings, your doctor can then diagnose some birth defects such as spinal abnormalities, renal disorders, heart defects and limb deformities. 

If your scan is flagged for possible heart-related abnormalities, your doctor will order a fetal echocardiography to examine the heart in more detail.

Genetic screenings

During the first trimester, your doctor can test your blood for pregnancy-associated plasma protein A and human chorionic gonadotropin. Any abnormal result means you’re at a higher risk for chromosomal birth defects.

Cell-free fetal DNA testing is one of the more common options to screen for Down syndrome, Trisomy 18 and Trisomy 13 during a pregnancy. The key word here is a screening test. By using your blood, the test can estimate if your child is at a higher risk of developing a condition such as Down syndrome. The screening can be performed after 10 weeks gestation.

If at any point a screening shows an increased risk of a birth defect, an amniocentesis or a chorionic villus sampling (CVS), can be used to diagnose chromosomal and neural tube defects. 

An amniocentesis is a procedure that uses a needle to extract amniotic fluid that surrounds the fetus. The fluid is then tested for various genetic and chromosomal conditions. A CVS takes sample tissue from the placenta to detect Down syndrome, cystic fibrosis, sickle cell disease, TaySachs disease, Trisomy 18 and Trisomy 13. The difference between the two tests is an amniocentesis can detect neural defects, while a CVS can’t.

Some birth defects take advanced testing to detect. A whole-exome sequencing (WES) test after birth can be conducted to look for genetic conditions that previous tests didn’t diagnose. 

Newborn exam

Your baby will undergo a comprehensive exam once they are born. During this exam, your doctor will confirm any suspected or new birth defects. Some birth defects, such as anorectal malformations, may not show up on an ultrasound but can be visualized during the exam.

Prenatal/postnatal MRI

While ultrasounds can diagnose common birth defects, this type of imaging has its limitations. For more comprehensive imaging, your doctor may order an MRI to examine specific parts of the fetus while still in the womb or after delivery to follow up on a possible defect. 

Developmental milestones

Attending prenatal checkups and staying on top of your child’s health can help with an early diagnosis, which can help put in a plan in place to meet their needs. For example, a prenatal diagnosis of pulmonary hypoplasia (small, underdeveloped lungs) can alert your doctors to have a plan in place for birth. This may include relocating to a neonatal intensive care unit that can care for newborns in respiratory distress.

If your child has been diagnosed with a birth defect, it’s beneficial to have a plan in place for their care. Whether it’s prenatal care for a high-risk pregnancy, neonatal care or pediatrics, our team of medical professionals at INTEGRIS Health can help guide you through your child’s development.