The Prenatal Genetic Testing Timeline: A Week-by-Week Look at Screening Options

Gestation

Prenatal tests are common and frequent during pregnancy to help assess your and your baby’s well-being as well as the healthy progression of your pregnancy. Your doctor will guide you through the process and may offer additional tests, depending on factors like your health and medical history.

Common Tests You’ll Undergo During Pregnancy

During the first few visits with your OBGYN, you’ll undergo a number of tests and exams – including blood pressure checks, a weight assessment, and a general physical exam. Throughout your pregnancy, your doctor is likely to order urine tests to check for gestational diabetes and preeclampsia, as well as monitor your weight and blood pressure.

Additional Testing Options for Genetic Defects

Though ultrasounds to assess your baby’s development are a regular part of any pregnancy, additional screening options may be available to you if you and your partner are found to be at a high risk of having a baby with a genetic condition. Undergoing these tests will help your medical team assess the likelihood that your baby could develop certain genetic disorders.

A common genetic condition that can be screened for during pregnancy is Down syndrome, which is more likely to occur if the mother is of advanced maternal age 35 or older at the time of birth, as well as if the couple has had another child with Down syndrome.  There are three to four principal tests to assess risk for Down syndrome (or another genetic condition) during pregnancy:

  1. Week 9 onward: DNA screening.  Noninvasive prenatal testing (NIPT), available from week 9 of gestation, use a blood sample from the mother to assess the baby’s risk of developing a number of genetic disorders (including Edwards syndrome and Patau syndrome, also called trisomy 13).  This test will not provide a definitive answer, but is a very low-risk and easy way to learn your baby’s risk, and to decide whether the risk of amniocentesis is worth it.
  2. Weeks 10-13: Chorionic villus sampling.  A more invasive, but definitive, diagnostic test is chorionic villus sampling.  In this procedure, a sample of chorionic villi is taken from the placenta for analysis.  There are risks involved in this kind of testing, and your doctor will discuss them with you in detail prior to the procedure.
  3. Weeks 11-14: Nuchal Translucency.  A common test administered between weeks 11 and 14 is a non-invasive test for Down syndrome called the “nuchal translucency test.”  During this test, your healthcare provider will use an abdominal ultrasound to measure the nuchal fold, an area of tissue at the back of an unborn baby’s neck.  Doctors use the measurements to determine whether this area of the neck is larger than normal, a common indicator of Down syndrome.  It is important to note that this test only assesses the risk for Down syndrome, and not any other disorder.
  4. Week 15 onward: Amniocentesis.  This is another test that your doctor will recommend if initial screenings show a potential for a genetic disorder, or if the parents are at an elevated risk (the mother is of advanced maternal age, or a genetic condition runs in the family). During an amniocentesis, a sample of amniotic fluid is extracted from the uterus and tested.  This procedure carries some risk, which your doctor will explain before the procedure is performed.

At each stage of your pregnancy, a number of different tests will be offered to you that will provide valuable information about your and your baby’s health. Your doctor or genetic counselor can help you understand your testing options and explain the outcome of any tests, along with possible treatment options, either during pregnancy or after birth.

Resources:

https://medlineplus.gov/ency/article/007561.htm

https://www.sequenom.com/edwards-syndrome-testing

http://www.webmd.com/baby/chorionic-villus-sampling#1 

https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=85&ContentID=P01241 

https://www.nichd.nih.gov/health/topics/preeclampsia/conditioninfo/Pages/risk.aspx 

http://www.mayoclinic.org/diseases-conditions/down-syndrome/