A birth defect can be found before birth, at birth, or any time after birth. Most birth defects are found within the first year of life. The mother’s blood can be tested during the first three months of pregnancy to look for proteins in the blood that suggest certain chromosomal disorders, such as Down syndrome. An 11 to 13 week ultrasound, which creates a picture of the baby, will look for extra fluid which may suggest a birth defect of the heart or chromosomal disorder. A second trimester ultrasound taken in the fourth through sixth month of pregnancy is used to check the size of the baby and look for birth defects or other problems. If the result of a screening test is abnormal, doctors do additional tests to see if the unborn baby has birth defects.