Pregnancy Stages / Development


Prenatal Testing

Find out what to expect during prenatal testing including Screening Tests, Targeted Ultrasound, Maternal Serum Marker Screening Test, Nuchal Translucency Screening (NTS), and Diagnostic Tests like Amniocentesis and Chorionic Villus Sampling (CVS).

Prenatal Testing

Prenatal testing is one of the most important parts of a healthy pregnancy. These tests will help determine if your fetus is viable, as well as whether it is developing as it should. It's very important that you keep all of your appointments for these tests! In this article, we'll be discussing the different types of prenatal tests you can expect.

Key Points

  • Screening tests can help give you an idea of the odds of your baby being born with certain genetic defects.
  • A targeted ultrasound will generally be prescribed between 18 and 20 weeks. A lot of developmental defects can be seen at this stage, but not all of them.
  • There are tests that can be performed to determine if there are any issues with your baby's chromosomes. These tests carry a small risk of miscarriage, but are still highly recommended.

An Introduction to Prenatal Testing

Your doctor will give you a schedule for your prenatal visits. A typical schedule includes visiting your doctor about once each month during your first six months of pregnancy, every two weeks during the seventh and eighth month of pregnancy, and then weekly in the ninth month of pregnancy.

If you are over 35 years old or your pregnancy is high risk because you have certain health problems (like diabetes or high blood pressure), your doctor will probably want to see you more often. The first time you see your doctor you'll probably have a pelvic exam to check your uterus. You'll also likely receive a pap test. After the first visit, most prenatal visits will include:

  • Checking the baby's heart rate.
  • Checking your blood pressure.
  • Checking your urine for signs of diabetes.
  • Measuring your weight gain.

Prenatal Tests and Procedures

While you are pregnant your doctor may suggest a number of laboratory tests, ultrasound exams, or other screening tests. Read on to find out the basics of the most common tests done during pregnancy.

Screening Tests

Screening tests measure the risk of having a baby with some genetic birth defects. Birth defects are caused by problems with a baby's genes, inherited factors passed down from the mother and the father. Birth defects can also occur randomly in people with no family history of that disorder. Women over the age of 35 have the greatest risk of having babies with birth defects.

The benefit of screening tests is that they do not pose any risk to the fetus or mother. But screening tests cannot tell for sure if the baby has a birth defect. So, they do not give a definitive yes or no. Instead, screening tests give the odds of your baby having a birth defect based on your age. Women under the age of 35 will find out if their risk is as high as that of a 35 year old woman. For women over age 35, screening tests will help them find out if their risk for their age is higher or lower than average.

Targeted Ultrasound

The best time to receive this test is between 18 and 20 weeks of pregnancy. Most major problems with the way your baby might be formed can be seen at this time. But some problems like clubbed feet and heart defects can be missed on ultrasound. Your doctor also will be able to see if your baby has any neural tube defects, such as spina bifida. This test is not the most accurate for finding out whether your baby has Down syndrome. Only 1 in 3 babies with Down syndrome have an abnormal 2nd trimester ultrasound. In most cases, your doctor can find out the sex of your baby by using an ultrasound. If you want to find out the sex of your baby at birth, make sure you inform your doctor so they know to keep this bit of info from you.

Maternal Serum Marker Screening Test

This blood test can be called by many different names including multiple marker screening test, triple test, quad screen, and others. This test is usually given between 15 and 20 weeks of pregnancy. It checks for birth defects such as Down syndrome, trisomy 18, or open neural tube defects. Doctors take a sample of your blood. They then check the blood for three chemicals: alpha-fetoprotein (AFP) (made by the liver of the fetus) and two pregnancy hormones: estriol and human chorionic gonadotropin (hCG). Sometimes, doctors test for a fourth substance in the blood called inhibin-A. Testing for inhibin-A may improve the ability to detect fetuses with a high risk of Down syndrome.

Higher levels of AFP are linked with open neural tube defects. In women age 35 and over, this test finds about 80% of fetuses with Down syndrome, trisomy 18, or an open neural tube defect. In this age group, there is a false positive rate (having a positive result without actually having a fetus with one of these health problems) of 22%. In women under age 35, this test finds about 65% of fetuses with Down syndrome, and there is a false positive rate of about 5%.

Nuchal Translucency Screening (NTS)

This new type of screening can be done between 11 and 14 weeks of pregnancy. It uses an ultrasound and blood test to calculate the risk of some birth defects. Doctors use the ultrasound exam to check the thickness of the back of the fetus' neck. They also test your blood for levels of a protein called pregnancy-associated plasma protein and a hormone called human chorionic gonadotropin (hCG). Doctors use this information to tell if the fetus has a normal or greater than normal chance of having some birth defects.

In an important recent study, NTS found 87% of cases of Down syndrome when done at 11 weeks of pregnancy. When NTS was followed by another blood test done in the second trimester ( maternal serum screening test), 95% of fetuses with Down syndrome were identified. Like all screening tests, the results are sometimes misleading. In 5% of women who have NTS, results show that their babies have a high risk of having a birth defect when they are actually healthy. This is called a false positive. To find out for sure if the fetus has a birth defect, NTS must be followed by a diagnostic test like chorionic villus sampling or amniocentesis.

NTS is not yet widely used. If you are interested in NTS, talk to your doctor. If they are unable to do the test, they can refer you to someone who can. You should also call your insurance company to find out if they cover the cost of this procedure. NTS allows women to find out early if there are potential health problems with the fetus. This may help them decide whether to have follow-up tests.

Diagnostic Tests

Diagnostic tests can give definite “yes” or “no” answers about whether your baby has a birth defect. But, unlike screening tests, they are invasive or come with a risk of miscarriage. Amniocentesis and chorionic villus sampling (CVS) are the two most commonly used. Both tests are more than 99% accurate for finding these problems. These tests also can tell you your baby's sex. In most cases, results take about two weeks.


This test is performed in pregnancies of at least 16 weeks. It involves your doctor inserting a thin needle through your abdomen, into your uterus, and into the amniotic sac to take out a small amount of amniotic fluid for testing. The cells from the fluid are grown in a lab to look for problems with chromosomes. The fluid also can be tested for AFP. About 1 in 200 women have a miscarriage as a result of this test.

Chorionic Villus Sampling (CVS)

This test is performed between 10 and 12 weeks of pregnancy. The doctor inserts a needle through your abdomen or inserts a catheter through your cervix in order to reach the placenta. Your doctor then takes a sample of cells from the placenta. These cells are used in a lab to look for problems with chromosomes. This test cannot find out whether your baby has open neural tube defects. About 1 in 200 women have a miscarriage as a result of this test.

What Happens if an Issue is Detected?

If your doctor detects an issue with your pregnancy, they'll recommend a treatment plan to address it. For example, if they feel you're gaining too much weight, they will recommend an alternative nutrition plan.

In some cases, a doctor may recommend that you terminate your pregnancy. While this can be an incredibly difficult thing to hear, if there's something catastrophically wrong with the fetus it's often the best idea. It may also be necessary for your own safety in certain instances. Keep in mind that abortion is not legal in all states; you may need to travel to a “safe haven” state if you choose to terminate your pregnancy due to issues with the fetus.

What you choose to do about an issue with your fetus is your decision. It is a complicated decision that takes time to think over, but in the end you must do what you feel is right.

None of the information provided in this article should be taken as medical advice. If you are experiencing issues with your pregnancy, or have any concerns or questions about your health, please seek the advice of a qualified medical professional.

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