According to the March of Dimes, about 1 in 33 babies born each year in the U.S. has a birth defect.

That's why experts advise that you visit your doctor before planning to become pregnant. This is especially important if you have chronic health conditions.

Cleft lip and cleft palate are birth defects of the mouth and lip. Cleft lip with or without cleft palate happens in about 1 in 1,000 births. These problems occur early in pregnancy. The sides of the lip and the roof of the mouth don’t join together as they should. A child can have cleft lip, cleft palate, or both. Most babies born with a cleft are otherwise healthy, with no other birth problems. Down syndrome is a genetic disorder that includes a combination of birth defects. These include intellectual problems and certain facial features. Often they also include heart defects, visual and hearing problems, and other health problems. These problems vary greatly in how severe they are. According to the CDC, Down syndrome affects about 1 in 700 babies. The World Health Organization lists heart defects, neural tube defects, and Down Syndrome as the most common severe congenital disorders.

Smoking raises the risk for miscarriage or damage to developing fetal organs. Alcohol and illegal drugs can raise the risk for fetal problems, miscarriage, and lifetime disabilities.

If a person is not immune to rubella, infection during pregnancy can cause a group of birth defects called the congenital rubella syndrome. Defects include decreased growth, intellectual problems, small head, congenital cataracts or cloudiness of the cornea, deafness, and heart defects.

Taking folic acid supplements may lower the risk for a group of conditions called neural tube defects by 50%.

This infection can be passed to humans through cat feces. It can seriously harm an unborn baby. Infection during pregnancy can cause premature delivery, low birth weight, intellectual problems, muscle movement problems, small head, small eyes and blindness, seizures, hydrocephalus, and damage to the liver and blood-forming organs.

Many prescription and over-the-counter medicines aren't safe during pregnancy. Check with your health care provider before taking any medicine or supplement.

Amniocentesis often is done between the 15th and 20th week of pregnancy. Down syndrome is one of the most common genetic chromosome problems tested for. The number of conditions that can be diagnosed by amniocentesis increases every year. Amniocentesis can be used to diagnose many chromosome problems, DNA-gene problems, and enzyme and amino acid problems. In late pregnancy, amniocentesis can even help find out how mature the baby's lungs are.

Being 35 or older increases the risk of having a child with chromosome problems. This is especially true for trisomy 21, also known as Down syndrome.