University of Nebraska Medical Center

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Prenatal Diagnosis

Most prospective parents look forward to pregnancy with excitement and some degree of anxiety. These feelings are part of every pregnancy. Ultimately, the health of the baby is the major focus.

Although most babies are born healthy, 3-4 out of every 100 children have an abnormality of development (birth defect) that is recognizable at the time of birth. Birth defects are disorders or malformations that may affect an infant's appearance, health, or ability to learn. Some birth defects are inherited and may be passed on in families. Others are the result of accidents that occur when the egg or sperm are formed. A few are due to exposure to hazardous agents during pregnancy. In some cases, the cause of the defect is unknown.

Currently, most birth defects cannot be treated until after a baby is born. After delivery, there may be special medical and surgical treatments needed for physical birth defects. Infant stimulation and special education services allow the developmentally delayed child to develop to the maximum potential. Even with the most careful treatment, some children with serious birth defects or genetic disorders may have lifelong limitations or will not survive.

Prenatal diagnosis refers to a collection of techniques or tests used to gather information about the developmental status of the fetus (unborn baby) before delivery. Many birth defects and genetic disorders can be detected through prenatal diagnosis. However, these tests cannot guarantee that a baby will be free of all birth defects. Prenatal diagnosis and genetic counseling may help to reassure parents that their child will be free of some of the more common birth defects.

Every couple has a 3-4% chance of having a child with a birth defect regardless of family history. There are factors, however, which can increase this "background risk" for a particular couple. When a woman's chance for having a child with a birth defect is greater than this background risk, she should be offered prenatal diagnosis and counseling. The most common reasons recognized for an increased risk include:

A mother who will be age 35 or older by her due date.
A couple with a chromosome abnormality in a previous pregnancy.
A known chromosome rearrangement in the mother or father.
A family history of neural tube defect [open skull (anencephaly), or open spine (spina bifida)].
A family history or known carrier status of a genetic disorder for which a prenatal test is available.
Exposure to a medicine or environmental/occupational agent previously reported or suspected to cause problems in the fetus.
Concerns raised by ultrasound exam, prenatal screening procedures, or pregnancy complications.

Several tests can be used to gather important information about the developing fetus. These include:

Maternal serum alpha-fetoprotein (MSAFP) - blood test on mother
Quad Fetal Risk Assessment - blood test on mother
Ultrasound (sonogram) - harmless sound waves which produce a picture on a viewing screen
Amniocentesis (amnio) - obtaining a small amount of fluid surrounding the fetus
Chorionic villus sampling (CVS) - obtaining a small piece of the placental tissue
Percutaneous umbilical blood sampling (PUBS or cordocentesis) - obtaining a small blood sample from the fetus

Options

Most individuals having prenatal diagnosis receive normal test results and are reassured about the health of the baby. In many cases, waiting for test results is the most difficult. For some people, however, testing shows an abnormality. Professionals are available to provide the families with the information and options needed to make the best decision for each situation. Depending on the results, families may face some difficult decisions.

In some cases the problems may be so severe that if the fetus survives until term, the baby will die shortly after birth. While some families may choose to interrupt the pregnancy, others may use the information to prepare for the pregnancy and delivery. Many of these babies may experience problems late in the pregnancy. Knowing in advance that these may occur can allow the family and doctors to avoid increased risks to the mother such as emergency cesarean section. Plans to make the baby comfortable rather than pursue heroic measures can be discussed in advance.

When survival is likely, knowing about a particular problem may allow health care workers to improve the outcome. Fetal assessment during delivery and the type and timing of delivery may be altered. Arrangements may be made for planned delivery at a time and place when specialists are available to treat the baby. Parents and other family members can prepare to deal with the situation in advance, rather than at a time when they are physically and emotionally drained.

Prenatal diagnosis can obviously raise some difficult questions. Deciding whether or not to have prenatal diagnosis depends on specific risks and concerns, family situations, and personal beliefs. It is important that all questions are answered before making any decision about testing and possible outcome. Again, in most cases, prenatal diagnosis will provide reassurance about the health of the baby allowing couples to enjoy the remainder of the pregnancy and make plans for years to come.

Other Prenatal Diagnostic Options

Human Genetics Laboratory