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PRENATAL TESTING

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Prenatal testing can be a multi-edged sword. Usually, test results are reassuring, which puts expectant parents’ minds at ease. But some people argue that because birth defects are rare, these tests in most cases cause undue stress; others argue that they allow people to create “designer” children. Then there are the parents who discover very real, sometimes dire, problems with their babies and face the decision of whether to keep or terminate a pregnancy. Testing is a difficult and confusing issue, and what’s right for one family may be entirely wrong for another.

Some women opt out altogether, claiming that even if a problem were detected, they would never terminate a pregnancy. Others choose to undergo blood screening tests but nothing invasive, such as amniocentesis. Still others say yes to every procedure offered to them, wanting to gather as much information as possible about the fetus’s health—and, hopefully, reduce their anxiety along the way.

“Testing is a very sensitive issue, and a very personal one,” says Barbara M. O’Brien, M.D., a geneticist and maternal-fetal medicine specialist at Women & Infants Hospital in Providence, R.I. “Patients can feel pressured to opt into screening, but they shouldn’t be. It’s a personal decision.”

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The topic can be so delicate that prospective parents should start considering it very early, even when they begin planning a pregnancy. “The clock is ticking once you conceive,” explains certified nurse-midwife Barbara L. McFarlin, Ph.D., C.N.M., of the department of women, children and family health science at the University of Illinois at Chicago College of Nursing. “There are certain windows when tests have to be completed.” Following are the most common screening and diagnostic tests currently being given, along with a few other types most moms-to-be have. But which you are offered, and which you choose to undergo, may vary according to your age, where you live, your personal or family history, and many other factors.

TESTS TO CONFIRM PREGNANCY

A missed menstrual period is usually the first sign of pregnancy. Tests to confirm pregnancy detect a pregnancy hormone called human chorionic gonadotropin (βhCG).

The various tests include:

  • Home test kit – these are available from pharmacies. A typical kit includes special paper that is sensitive to the presence of βhCG in urine. It is important to use a home test kit according to the manufacturer’s instructions, or false results can occur. Always confirm your results with your doctor. Pregnancy tests taken by your doctor are rarely inaccurate.
  • Urine test at the doctor’s office – the doctor can test your urine for βhCG.
  • Blood test – a test of the βhCG levels in your blood can be accurate within one week or so of conception.

The new test scans a mother's blood for bits of a fetus's DNA.

TYPES OF PRENATAL TESTING

Prenatal testing includes both screening tests and diagnostic tests:

  • Screening tests. Prenatal screening tests can identify whether your baby is more or less likely to have certain birth defects, many of which are inherited disorders. These tests include blood tests, a specific type of ultrasound and prenatal cell-free DNA screening. Prenatal screening tests are usually offered during the first or second trimester. Screening tests can’t make a definitive diagnosis. If you get a positive result your health care provider will discuss your options for a diagnostic test to confirm the diagnosis.
  • First trimester screening tests. During your first trimester, your health care provider will offer a blood test and an ultrasound to measure the size of the clear space in the tissue at the back of a baby’s neck (nuchal translucency). In Down syndrome and in certain other conditions, the nuchal translucency measurement is abnormally large.
  • Second trimester screening tests. During the second trimester, your health care provider will offer an additional blood test called the quad screen. This test measures levels of four substances in your blood. Results indicate your risk of carrying a baby who has certain chromosomal conditions, such as Down syndrome. The test can also help detect neural tube defects — serious abnormalities of the brain or spinal cord.
  • Prenatal cell-free DNA screening. This sophisticated blood test examines fetal DNA in the maternal bloodstream to screen for the increased chance for specific chromosome problems, such as Down syndrome. This screening might be considered if your age, family history or medical history suggests an increased chance for having a baby with certain chromosomal abnormalities. It also might be considered if another screening test, such as the nuchal translucency or quad screen, indicates a possible problem. This screening can also provide information about a baby’s sex and rhesus (Rh) blood type.
  • Diagnostic tests. If a screening test or prenatal cell-free DNA screening indicates a possible problem — or your age, family history or medical history puts you at increased risk of having a baby with a genetic problem — you might consider an invasive prenatal diagnostic test. A diagnostic test is the only way to be sure of a diagnosis. Some diagnostic tests, such as chorionic villus sampling — in which a sample is taken from the placenta — or amniocentesis — in which a sample of amniotic fluid is removed from the uterus — carry a slight risk of miscarriage.

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TESTS TO MONITOR THE HEALTH OF THE MOTHER AND THE BABY

Pregnancy care involves regular appointments with your doctor or midwife to monitor your pregnancy and the baby’s growth. Care includes tests that check on the health of both you and your baby, and help to identify any problems with the pregnancy.

Routine prenatal tests may include:

  • blood tests at different stages of the pregnancy, such as blood group, iron levels, checks for maternal diabetes and infections
  • ultrasound (first trimester) – a painless, non-invasive scan done within the first three months of pregnancy. This can be used to confirm the number of babies and helps to calculate the date you are due to give birth. This is known as your estimated due date.
  • ultrasound (second trimester) – this is usually performed between 18 and 20 weeks. It is used to check the baby’s development, and monitor the size and location of the placenta. The baby’s sex can often be determined (if you wish to know), although this may not be 100 per cent accurate.
  • ultrasound (third trimester) – in the last three months of pregnancy, an ultrasound may be offered to check the baby’s growth, fluid levels around the baby and the positioning of the placenta.

SUMMARY

Prenatal testing provides information about your baby’s health before he or she is born. Some routine tests during pregnancy also check on your health. At your first prenatal visit, your healthcare provider will test for a number of things, including problems with your blood, signs of infections, and whether you are immune to rubella (German measles) and chickenpox.

Throughout your pregnancy, your healthcare provider may suggest a number of other tests, too. Some tests are suggested for all women, such as screenings for gestational diabetes, Down syndrome, and HIV. Other tests might be offered based on your:

  • Age
  • Personal or family health history
  • Ethnic background
  • Results of routine tests

Some tests are screening tests. They detect risks for or signs of possible health problems in you or your baby. Based on screening test results, your doctor might suggest diagnostic tests. Diagnostic tests confirm or rule out health problems in you or your baby.

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