Prenatal tests

What to expect during prenatal tests

Prenatal tests are an essential tool your healthcare provider will use to detect developmental problems or other health issues. Here’s what you can expect during each one.

Routine prenatal tests
Most pregnant women will visit their healthcare provider every four to six weeks in their first trimester, as well as most of their second. Then, 30 weeks into your pregnancy, your visits will likely increase to every two to three weeks and, after 36 weeks, you’ll be heading to the doctor’s office every one to two weeks until you deliver.

At each of these visits you can expect the following:

  • Weigh-ins Pregnancy weight gain is inevitable and your baby’s development depends on it. The amount you need to gain depends on a number of factors, including your body mass index (BMI) and pre-pregnancy weight. Work with your doctor to determine what’s appropriate for you. 
  • Blood tests These will identify your blood type, check your red blood cell, iron levels, and determine your immunity to infectious diseases (such as German measles, chicken pox, hepatitis B, syphilis and HIV). 
  • Blood pressure Your doctor will check your blood pressure at every visit—high blood pressure could be a sign of hypertension or early warning of “pre-eclampsia” (the term for high blood pressure with proteins in the urine during pregnancy). 
  • Urine tests Your urine will be monitored at each visit for signs and symptoms of gestational diabetes, kidney disease, and urinary tract infection (UTI). 
  • Doppler ultrasound By about 12 weeks, you may be able to hear your baby’s heartbeat with a handheld Doppler ultrasound (this can depend on your baby's position in your uterus, your weight and the accuracy of your due date).

Other important tests on the horizon

  • Ultrasound At around 18 to 20 weeks, you will have a detailed ultrasound that examines your baby’s development and checks for any physical abnormalities. This is also when you can discover the sex of your baby, if you desire. 
  • Glucose screening test Between 24 and 28 weeks, you’ll be given this test to determine if you have gestational diabetes, which is one of the more common health problems during pregnancy. 
  • Group B Strep At around 36 weeks, this test will determine whether you have group B streptococci, which could be passed on to your baby during a vaginal birth.

Genetic screening
In addition to routine prenatal testing, you may decide to have screening or diagnostic testing for genetic disorders, such as Down syndrome or Trisomy 18. Most doctors will recommend tests if you are over the age of 35 or if you have a family history of birth defects. If a serious condition is determined, further diagnostic tests will be scheduled. After that, women have the option of continuing the pregnancy, or choosing to terminate the pregnancy.

Integrated Prenatal Screening (IPS) is usually done in two steps. The first step, at 11–14 weeks of gestation, involves a blood test and a nuchal translucency (NT) scan which measures the nuchal fold thickness at the back of the baby’s neck. Another blood test is done between 15–20 weeks that looks for certain “markers” for Down’s syndrome in the mother’s blood. The tests are then combined to provide a risk estimation for Down’s syndrome.

The chance of having a child with Down syndrome increases with maternal age. (At 35 years, the risk of having a baby with Down syndrome is about one in 385.) Similarly, an alpha-fetoprotein (AFP) test may be done between 16 and 18 weeks of pregnancy. This test is designed to look for a protein produced by the fetus and helps rule out open Neural Tube Defect (NTD) such as open spina bifida (a birth defect where the spine and/or brain fail to develop properly in the womb), and anencephaly (when a part of the brain does not fully develop).

These early screening tests are designed to show your risks of having a baby with birth defects, which then gives you an opportunity to consider more invasive diagnostic testing, such as chorionic villus sampling (CVS) or amniocentesis, to find out for sure.