Birth Defects and Congenital Anomalies Symptoms & Causes

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How common are birth defects?

About 3 percent to 4 percent of babies are born with some type of birth defect.

What causes birth defects?

Most birth defects are caused by genetic or environmental factors or a combination of the two (multifactorial birth defects). In most cases, however, the cause is unknown.

Genetic or inherited causes include:

  • Chromosomal defects – caused by too few or too many chromosomes, or problems in the structure of the chromosomes. Example includes Down syndrome (and extra copy of chromosome 21 and sex chromosome abnormalities (missing or extra copies of the sex chromosomes X or Y).

  • Single gene defects – a mutation in one gene causes the defect.

  • Dominant inheritance – A person can inherit a genetic disease when one parent (who may or may not have the disease) passes along a single faulty gene. Examples include achondroplasia and Marfan syndrome

  • Recessive inheritance – occurs when both parents who do not have the disease pass along the gene for the disease to the child. Examples are cystic fibrosis and Tay Sachs.

An environmental cause can include a drug, alcohol or a disease the mother has that can increase the chance for the baby to be born with a birth defect. An agent that can cause a birth defect is known as a teratogen.

Multifactorial birth defects are caused by a combination of genes and environmental exposures. In other words, a person can inherit a gene that increases sensitivity to an environmental trigger. Examples include cleft lip or palate, certain heart defects, and neural tube defects.

What are the most common birth defects?

How can I lower my chances of having a child with a birth defect?

There are many steps a woman can take to lower her chances of having a child with a birth defect, including staying healthy before deciding to become pregnant. That's because a woman often does not know she is pregnant in the first few weeks, which can be crucial for the health and development of the baby.

Other steps you can take throughout your pregnancy include:

  • Stop smoking – Babies born to mothers who smoke tend to be lower birthweight; in addition exposure to secondhand smoke can harm the fetus

  • Eat a healthy diet – Eating a balanced diet before and during pregnancy is not only good for the mother's overall health, but essential for providing the developing fetus with essential nutrients for proper growth and development.

  • Maintain a healthy weight – Women who are overweight may experience medical problems such as high blood pressure and diabetes, and women who are underweight may have babies with low birthweight.

  • Medical management of preexisting conditions – Take control of any current or preexisting medical problems, such as diabetes or high blood pressure.

  • Folic acid – Taking 400 micrograms of folic acid each day can help lower the risk of neural tube defects, or birth defects of the brain and spinal cord. The vitamin is also found in some green leafy vegetables, nuts, beans, citrus fruits and fortified breakfast cereals.

  • Avoid exposure to alcohol and drugs during pregnancy – Be sure to inform your physician of any medications and herbal supplements you are taking, since they can all have adverse effects on the developing fetus.

  • Avoid exposure to harmful substances – These include lead, pesticides and radiation (i.e., X-rays), which may harm the developing fetus.

  • Lower your risk for infection. Pregnant women should avoid eating undercooked meat and raw eggs and avoid all contact and exposure to cat feces and cat litter, which may contain a parasite, toxoplasma gondii, that causes toxoplasmosis. Other sources of infection include insects that have been in contact with cat feces.

  • Take a daily vitamin – Begin taking a prenatal vitamin daily, prescribed by your doctor, to make sure your body gets all the necessary nutrients and vitamins needed to nourish a healthy baby.

  • Dealing with domestic violence – Women who are abused before pregnancy may be at risk for increased abuse during pregnancy. Your doctor can help you find community, social and legal resources to help you deal with domestic violence.

What is a preconception examination?

A preconception examination, also known as a preconception visit, is one of the best ways to ensure a healthy pregnancy. The goals are to assess your overall health and identify any risk factors that can complicate a pregnancy. A preconception examination can include any of the following:

  •  Family Medical History – a doctor will assess the medical history of both of your biological parents to see if any family member has had medical problems such as high blood pressure, diabetes or mental retardation.

  • Genetic Testing – a doctor will assess any possible genetic disorders that can be passed down to your child; some genetic disorders can be detected by blood tests before pregnancy.

  • Personal Medical History – to determine if you have any medical conditions that may require special care during pregnancy (anemia, epilepsy, diabetes, high blood pressure); to gather information about previous surgeries; and to obtain information about past pregnancies such as complications, losses and length of gestation.

  • Vaccination Status – to assess immunity to diseases such as rubella (German measles) that can cause miscarriage or birth defects. A vaccine can be given at least three months prior to conception to provide immunity.

  • Infection screening – to determine if a woman has a sexually transmitted infection, a urinary tract infection or another type of infection that can be harmful to her or to the fetus.

We are grateful to have been ranked #1 on U.S. News & World Report's list of the best children's hospitals in the nation for the third year in a row, an honor we could not have achieved without the patients and families who inspire us to do our very best for them. Thanks to you, Boston Children's is a place where we can write the greatest children's stories ever told.”
- Sandra L. Fenwick, President and CEO

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