Every mom-to-be hopes to give birth to a healthy baby. However some women, due to age or genetic makeup, are at greater risk of having a baby with a birth defect. Amniocentesis -- or amnio for short -- is a prenatal diagnostic test that uses a sample of the amniotic fluid that surrounds your baby in the womb to test for specific abnormalities. Amnio can rule out many potential problems, including inherited conditions like hemophilia and cystic fibrosis, chromosomal disorders like Down syndrome, and open neural tube defects (a malformation of the brain or spinal cord). The good news is that more than 95 percent of the amnios performed on high-risk moms reveal their babies to be free of the disorder for which they're being tested.

Amnio is not offered routinely to all pregnant women. It is considered an invasive procedure and carries a slight risk of miscarriage: According to the US Centers for Disease Control and Prevention, you have a one in 400 to one in 200 chance of having a miscarriage after the procedure -- that is, the highest risk is one-half of 1 percent. Outcomes are best when a highly experienced practitioner performs the test at a major medical center. Your doctor will probably recommend amnio if you fit one of the following categories:

•You will be 35 years old or older when your baby is born. The risk of carrying a baby with a birth defect increases as you age. For example, if you're in your 20s, you have about a one in 1,250 chance of carrying a child with a birth defect. That figure rises to one in 400 when you reach age 35 and jumps to one in 100 once you hit age 40.

•A previous screening procedure, such as a multiple marker test or a nuchal fold scan, suggests your baby may have a disorder. In such cases, an ultrasound is usually done first to look for indications of birth defects like Down’s syndrome. If the scan spots a likely problem, an amnio can confirm the diagnosis.

•You've already had (or been pregnant with) a baby with a birth defect.

•You or your partner have an inherited genetic disorder in your family history.

This test is typically done in your second trimester, between the 15th and 18th weeks of pregnancy. Amnio may also be performed during the third trimester to detect specific problems. If your baby has a blood type that is incompatible with yours, a condition called Rh disease, an amnio can determine whether your baby is anemic and needs a transfusion. If you need to deliver early (before 37 weeks) or you go into premature labor, an amnio can tell if the baby's lungs are mature enough to function properly. The test may also be used to confirm or rule out a uterine infection, particularly if the fluid-filled amniotic sac around your baby breaks prematurely.

Many hospitals make sure that women getting amnios make an appointment with a genetic counselor before the procedure. This is advisable because there are now first-trimester tests that may help women of any age define their risk of birth defects before getting amniocentesis.The counselor will go over any family history of genetic disease as well as advise women over 35 of their risk of having a baby with birth defects. Since amniocentesis also reveals the sex of the baby, the counselor will probably ask you if you'd like to know your baby's gender along with your test results. It's a matter of personal preference whether you and your partner want to know before your baby is born.

In most cases, you can bring someone with you for moral support during the procedure. To begin, you'll lie on an examination table and a technician will swab your belly with antiseptic. Then the technician or a doctor will use ultrasound to find a pocket of amniotic fluid a safe distance from both your baby and the placenta, the tissue that nourishes your baby. You'll need to have a full bladder for the ultrasound, so find out beforehand how much water you need to drink and when. This part of the procedure may take as long as 45 minutes.

Once the practitioner has pinpointed a safe spot, she will insert a long, fine, hollow needle through your abdomen and uterus and into the amniotic sac of fluid, all under continual ultrasound guidance. Don't worry -- your baby is extremely unlikely to get pricked by the needle. If by some odd chance the needle does come in contact with your baby, he'll move away quickly, just as you would if you touched something sharp. The technician will withdraw a small amount of fluid, less than an ounce, or about one to two tablespoons, and then slowly remove the needle. The sample will contain live fetal cells that normally float in the amniotic fluid. Your body makes more fluid to replace what's taken.

You may experience cramping, pinching, or pressure during the procedure. You can opt to have your belly numbed first with a local or topical anesthetic, but some women who have experienced it both ways say the pain from the anesthetic injection is worse than the amnio itself. The choice is yours. The amount of pain or discomfort you may feel is an individual thing that can even vary from one pregnancy to the next.

When the procedure is completed, your practitioner may use an external fetal monitor to listen to the baby's heartbeat in order to make sure that all is well. You'll want to take it easy for a few hours and avoid heavy lifting, prolonged standing, or strenuous exercise for the remainder of the day.

You may have some light cramping for a day or two. Some women -- around 1 to 2 percent -- experience significant cramping, light vaginal bleeding known as spotting, or leaking amniotic fluid . If you experience these symptoms, or develop a fever, call your doctor immediately.

A small amount of fluid leakage is nothing to worry about, but it's safer to report it anyway. For most women it's perfectly safe to resume normal activities the day after the amniocentesis. The clinic where you have the amnio should give you clear instructions. If you have any questions when you get home, be sure to call.

Your amniotic fluid is sent to a laboratory for analysis. First, the technicians will measure the amount of a chemical called alpha-fetoprotein, or AFP, in the fluid. High levels may indicate the potential for an open neural tube defect such as spina bifida. Low levels of AFP, in combination with other indicators, may suggest a chromosomal abnormality. If early screening tests or family history suggest a problem is possible, the technicians will also take some of your baby's cells from the fluid and allow them to multiply for a week or two in a cell culture. Then they'll test the cells for abnormalities. Complete results can take as long as three weeks, although some labs may be able to get them out in a little over a week.

What happens next depends on what disorder is diagnosed and what you decide to do about the new information you have. Unfortunately, today's healthcare professionals are able to confirm many more birth defects than they're able to treat after birth or even remedy prenatally. If your baby has a condition for which prenatal treatment is available, you'll want to discuss your options with your partner, healthcare team, and/or experts in this area.

If the baby has an ailment for which prenatal treatment is not yet available, you'll also want to discuss your situation with your partner, healthcare providers, genetic counselors, spiritual advisors, or any other support people. In some cases you'll want to prepare emotionally, practically, and financially for the arrival of a baby with a birth defect. In other circumstances you may decide to discontinue the pregnancy. The choice is a personal one and yours to make, once you've had a chance to consider all the factors involved.

-- Sarah Henry is a freelance writer whose health and parenting stories have appeared in The Washington Post, Los Angeles Times Magazine, Health, Hippocrates, Parenting and other publications.

References

First published June 14, 2005
Last updated April 1, 2008
Copyright © 2005 Consumer Health Interactive

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