Women's  Healthcare Topics is a website about pregnancy and your newborn baby.

Prenatal Testing

Reviewed by James Brann, M.D.

Routine Prenatal Testing

What testing will be done at my first OB visit?

Routine prenatal testing is suggested for all women early in their pregnancy. Your first doctor's appointment is when most of your testing will be performed. You will also find out how far along you are, your due date and discuss any medical problems you may have.

These prenatal tests will provide the doctor with information regarding your health and detect any possible problems regarding your pregnancy. Multiple tests, including many different types of blood tests, will be ordered at your first prenatal visit. Rest assured that each ordered blood test does not need to be drawn separately.

What tests will be done at my first prenatal visit?

Blood type and Rh factor - First your doctor will want to know your blood type and Rh factor. Blood types are A, B, AB or O. The Rh factor is either positive or negative.

Knowing your Rh factor is very important because it can affect your baby's health and development. For example, if you have Rh negative blood and your baby has Rh positive blood, you could create antibodies that may cause harm to your baby. These antibodies will destroy the baby's red blood cells.

Blood count - You will also have a test to check your blood count. If you have a low blood count (anemia), you will receive supplemental iron pills in addition to your prenatal vitamins.

Rubella immunity - Another blood test will identify if you have had the German measles, also known as “Rubella”. If you have not, you will need to avoid anyone who has the measles, as the Rubella virus can cause birth defects early in pregnancy. After you deliver your baby, you can receive a vaccine to guard against getting the measles.

Hepatitis B - A blood test will be done to check if you have Hepatitis B. If you test positive for having the infection, it is possible that you can pass it to your baby before birth. As a safety precaution, all babies are now vaccinated against Hepatitis B when they are born.

Sexually Transmitted Diseases (STD) -A test for sexually transmitted diseases (STD) will be done. If you are pregnant and have Syphilis and the disease is unrecognized and/or not treated, you can pass it on to your baby, causing serious health concerns for you both. Fortunately, if your blood test is positive for Syphilis, it can be treated during pregnancy.

HIV - Finally, a blood test will be given to check you for HIV (Human Immunodeficiency Virus). The HIV virus causes AIDS (Acquired Immune Deficiency Syndrome). If needed, you can be treated during pregnancy to reduce the risk of passing the AIDS’ virus to your baby.

Pap Test - At your first prenatal visit, a pelvic exam will be performed and a Pap test will be taken. The Pap test screens for pre cancer and cancerous cells of the cervix (opening to the uterus in the vagina). The cervical cells obtained by the Pap test will be sent to the lab and also checked for sexually transmitted diseases such as Gonorrhea and Chlamydia.

What tests will be done at each prenatal visit?

Urine tests - At all of your prenatal visits, your urine will be tested. These tests will check for sugar and protein in your urine. Small amounts of sugar in your urine can be normal during pregnancy, whereas high levels can mean you have diabetes.

Protein in your urine is not normal and can mean you have a bladder infection or kidney disease. One of the major signs of pre-eclampsia (high blood pressure in pregnancy) is protein in your urine.

Your weight -Your weight gain or loss will be monitored. It is normal for a woman to gain one third of your weight in the first 28 weeks of your pregnancy and gain two thirds of your weight in the last part of your pregnancy.

Blood pressure - Your blood pressure will be checked at each visit. A rising blood pressure may be a warning sign of pre-eclampsia.

Fundal height - The growth of your baby is watched by measuring the size of your uterus at each visit. A tape measure is used to measure the distance between your pubic bone and the top of the uterus. Generally this measurement (fundal height) gives your physician a handle on if the baby is growing at a normal rate or not.

Fetal movements - Your physician will want to know how active your baby was since the last visit. Your baby's movements are a great way to make sure everything is progressing on track. Note, usually you will not feel movements until about 17 – 20 weeks of pregnancy.

You should do fetal counts every day, especially during the last trimester. Most healthy babies have over 10 kicks or movements in two hours. If you perceive a significant change in fetal movement never wait longer than two hours to contact your physician.

Fetal heart rate - You will listen to your baby’s heart and count the beats at each visit. The normal baby’s heart rate is between 120 to 160 beats per minute.

What routine tests are performed later in my pregnancy?

Three major routine tests are performed in the third trimester of pregnancy. You will have your blood count rechecked, be screened for diabetes and tested for Group B Strep infection.

Blood count - Your blood count will be repeated when you are 28 weeks pregnant to make sure you have not developed anemia during your pregnancy.

Gestational diabetes -You will also have a diabetes test performed between 24 to 28 weeks. You will be required to drink a sugar solution called “glucola” before having your blood drawn. If you develop gestational diabetes, this is the time it is usually first recognized.

Group B Strep -Later in pregnancy, around 36 weeks pregnant, you will be checked for GBS (Group B Streptococcus or "Strep"). The test is performed using a swab to obtain cells from the vagina and the area around the anus. This is a very important test, and if positive, you will be treated with antibiotics during labor to prevent the baby from becoming infected.

What are genetic screening tests?

Depending on your medical history, you may have additional tests performed beyond routine prenatal testing. These tests are called genetic screening tests. The screening tests check for suspicion or an increase risk of having a baby with a birth defect. The tests will be offered to you during various stages of your pregnancy. Recommended genetic screening tests depend upon your medical history and your doctor's findings from you prenatal visits. It is the responsibility of your physician to explain to you the available genetic tests, why they would be needed, and their risks and benefits.

Is there an early genetic screening test?

Yes, there is a very simple first trimester screening test for genetic problems. If you have a family history of Down syndrome or other genetic disorder and you are over the age of 35, you will be offered a screening test at 11 to 14 weeks to determine your risk for a problem.

This test consists of blood testing along with an ultrasound examination of your baby's skin thickness on the back of its neck. This test will identify 80% of the cases of Down syndrome in pregnancy.

What are the later genetic screening tests?

Your baby can also be tested for Down syndrome later in pregnancy, usually at 15 and 20 weeks. The "multiple markers" blood test is offered during your second trimester and is used to assess your baby's risk, not only for Down syndrome, but neural tube defects (Spina Bifida) as well.

Two different multiple marker blood tests are available. One is called the "triple screen" and the other is the quadruple or "quad screen".

If your screening tests show an increased risk of Down syndrome or other genetic disorders, your doctor will discuss with you the suspected problem and will recommend further testing for a definite diagnosis. Diagnostic genetic testing will be offered.

What are the diagnostic genetic tests?

Diagnostic testing will give you a definite answer as to whether your baby has a problem and exactly what the problem is. The two main diagnostic tests are "amniocentesis" and "chorionic villus sampling."

1. Amniocentesis testing can be done both in the first and second trimester and is performed under a local anesthetic. To perform an amniocentesis your physician will place a needle through your skin into the bag of water surrounding the baby. A small amount of amniotic fluid and cells are sampled. Genetic testing is then performed from this fluid sample.

2. Chorionic Villus Sampling (CVS) can only be performed early in pregnancy. It requires obtaining a small tissue sample from the placenta, or afterbirth.

A screening test and follow up diagnostic test will allow your physician to properly plan and guide you in regards to the care that both you and your baby will need if a problem is found.

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