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Windows on the Womb

Select any one of the techniques listed below to find out more about it. The weeks during which doctors commonly use such techniques are listed with each technique.

Enhanced Alpha Fetoprotein | Amniocentesis | Chorionic Villus Sampling | Doppler device | Fetal Echocardiography | Ultrafast fetal MRI | Nuchal Translucency Test | Ultrasound scanning

Enhanced Alpha Fetoprotein or the Quad (AFP)
15 to 18 weeks

A protein produced by the baby's liver, alpha fetoprotein (AFP) normally enters the mother's bloodstream. In this test, blood drawn from the mother is examined for AFP; the amount of AFP in her blood determines the level of risk for disorders such as Down syndrome, neural-tube defects, abdominal-wall defects, and Edwards syndrome. High levels may mean a neural-tube defect or that some or all of the baby's brain material is missing. A low level can be an indication of Down syndrome. Because this is a screening test, showing only the baby's level of risk, follow-up testing for an abnormal level is recommended. There is no risk to the baby, but because as many as 5 percent of all women test positive, further testing often results. The vast majority of these women turn out to carry healthy fetuses.

Amniocentesis
16 to 18 weeks

Obstetricians typically recommend the use of amniocentesis for women more likely to be carrying a baby with abnormalities, such as older women (35 and above) or women with a family history of genetic diseases. An ultrasound prior to the test determines the baby's location, and then a specialist uses a small needle to withdraw about a tablespoon of the amniotic fluid surrounding the baby. Cells from the baby found floating in the fluid are cultured and examined to look for chromosomal disorders. Doctors use the test primarily to detect spina bifida or Down syndrome, but also Rh disease, fetal anemia, sickle-cell anemia, and to determine the baby's sex. Late in pregnancy, doctors use amniocentesis to find out if the baby's lungs are sufficiently developed and thus able to withstand, if necessary, a medically required premature birth. The U.S. Centers for Disease Control and Prevention estimates that the rate of miscarriage following amniocentesis is between one in 200 to 400 procedures.

Chorionic Villus Sampling (CVS)
10.5 to 13 weeks

As with amniocentesis, obstetricians may suggest using CVS, short for chorionic villus sampling, to detect genetic disorders such as Down Syndrome. In CVS, specialists perform an ultrasound to determine the position of the fetus and then remove fetal tissue by placing an instrument through the cervix or abdomen. Unlike amniocentesis, which can also detect Down syndrome, this test can be carried out much earlier in pregnancy, and test results are also available sooner. That means that if parents decide to terminate a pregnancy based on the results, they can do so as much as nine weeks earlier than in the case of amniocentesis, creating fewer risks to the mother's health. There is a 1 to 2 percent risk of miscarriage following the procedure.

Doppler device
6 weeks to term

A Doppler device is a small, portable machine that uses ultrasound waves to detect and magnify the baby's heartbeat. Doctors use this test during most office visits to verify that the baby is alive. After about the tenth week, a baby's heart rate can vary between 120 and 170 beats per minute. In the third trimester, obstetricians may use a variation of this test, known as umbilical cord Doppler, to examine the flow of nutrients between heartbeats, to ensure that the baby is receiving adequate nourishment. There is no known risk to the baby or the mother with this test.

Fetal Echocardiography
14 weeks to term

This test is essentially a very detailed ultrasound focussing on the structure and function of the heart. Doctors use it only when either siblings or parents have a history of heart defects, when other tests such as amniocentesis have produced abnormal results, when the mother has diseases that can affect the heart (such as diabetes or phenylketonuria), or when the fetus has been exposed to certain drugs. Most experts conduct the test between the 20^th and 22^nd week to ensure that they can see the heart clearly. There is no known risk to the baby or mother with this test.

Ultrafast fetal MRI
second or third trimester

MRI (magnetic resonance imaging) relies on a magnetic field and radio waves to "eavesdrop" on the body's electromagnetic transmissions. An MRI image can clarify the diagnosis of a fetal abnormality observed in an ultrasound and better prepare parents and their doctors for any interventions that may be needed to help the baby before or immediately after birth. It is especially helpful for examining certain tissues, such as the brain, that are encased in bone and would be difficult or impossible to see using ultrasound. MRI is not as widely available as ultrasound. It poses no known risk to the baby or mother.

Nuchal Translucency Test (NT Scan)
11 to 14 weeks

This test uses ultrasound to examine the fold of skin on the back of the baby's neck. At this early stage of development, the skin is so thin that fluid accumulates between it and the underlying structures. More fluid, which produces a thicker fold, can be a sign that the baby has a chromosomal abnormality, such as Down syndrome. This test is available at a number of university medical centers around the U.S. As with ultrasound, there is no known risk to the baby or mother.

Ultrasound scanning
5 weeks to term

Many women will have at least one ultrasound during their pregnancy. High frequency sound waves are directed at the fetus and the returning "echoes" form a live-action picture of the baby. Typically performed between 16 and 18 weeks, an ultrasound provides a general check of the baby's anatomy and can also help to date the pregnancy. Later on in pregnancy, ultrasound can gauge the baby's growth and development, determine the location of the placenta, and measure the amount of amniotic fluid. Three-dimensional ultrasounds, which are now becoming available at some health centers, provide a much clearer, more photographic image and make it possible to observe the baby from any angle, regardless of what position the baby is in during the procedure. There is no known risk to the baby or mother.

Windows on the Womb—Glossary

Down syndrome—In most cases caused by a third chromosome 21, Down syndrome results in mental retardation and other abnormalities. Children with Down syndrome have a widely recognized characteristic appearance.

Neural-tube defects—An NTD occurs in the neural tube, the part of the fetus that becomes the brain or spinal cord. NTDs result in the partial or complete absence of the brain, or in an opening of the spine. They are among the most common of all serious birth defects.

Abdominal-wall defects—Abdominal-wall defects feature a soft bulge of tissue or a small, localized swelling on the abdomen, most often caused by a hernia. A hernia is an area where muscles are weak enough to allow internal organs to protrude.

Edwards syndrome—Also known as trisomy 18, Edwards syndrome is associated with a third chromosome 18, which causes multiple physical abnormalities and severe mental retardation. Few infants survive beyond their first year.

Rh disease—When the baby is Rh-positive and the mother is Rh-negative, the mother's antibodies can cross the placenta and attack the baby's red blood cells, resulting in jaundice, anemia, brain damage, heart failure and death. Rh disease occurs only when the mother has previously been sensitized to Rh-positive red blood cells and has developed antibodies to them.

Fetal anemia—Fetal anemia occurs primarily when the mother's blood type is incompatible with the baby's, leading to the destruction of red blood cells in the baby's blood. This in turn results in an oxygen deficiency for the baby.

Sickle-cell anemia—In this chronic inherited disease, the normally round red blood cells become sickle- or crescent-shaped. When these abnormally shaped cells move through small blood vessels they can clog blood flow or break apart, causing sudden severe pain in many areas of the body, damage, or anemia.

Diabetes—Diabetes is a life-long disease in which the body produces too little insulin or is unable to use the insulin properly. The result can be dangerously high blood-sugar levels, which, when untreated, starve cells of energy and over time can damage the eyes, kidneys, nerves or heart.

Phenylketonuria—Phenylketonuria is a rare genetic disorder in which the body is unable to properly metabolize the amino acid phenylalanine, one of the eight essential amino acids found in protein-containing foods. The accumulation of phenylalanine in the blood and body tissues can cause severe mental retardation and developmental delays if not treated.

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