Early detection of complications in pregnancy
February marks pregnancy awareness week.
First trimester biomarker testing reduces unnecessary invasive tests
What is prenatal screening?
Prenatal screening tests are methods to obtain more information about the risks of certain birth defects, e.g., chromosomal abnormalities (aneuploidies) for instance Down syndrome, in pregnancies and to identify pregnancies at risk of other complications, e.g., stillbirth and pre-eclampsia (a condition in pregnancy characterized by high blood pressure).
What is the difference between invasive and non-invasive prenatal tests?
Non-invasive prenatal tests are screening tests. These blood and ultrasound tests performed on the mother and completely safe for the pregnancy and unborn baby. These tests determine the risk or chances of complications and abnormalities:
- Biomarker or blood tests check the levels of certain chemicals in the mother’s blood to see if they are higher or lower than expected.
- Prenatal cell-free DNA (cfDNA) screening, also known as non-invasive prenatal screening (NIPT) uses a blood sample from the mother to analyze bits of fetal DNA that have leaked into her bloodstream to screen for the increased chance for specific chromosome problems.
Prenatal screening tests don’t test the developing baby directly. Prenatal screening tests accurately predict if the risk for having a baby with a specific condition is higher or lower than average. They accurately measure risk factors that are used to predict risk. Everyone has a risk of having a pregnancy with birth defects and these screening tests move that risk up or down. Screening tests can’t tell for sure if there is a birth defect in a pregnancy, it can however take a large group of people and narrow it down to a smaller group of people whose risk is high enough to justify more testing. Screening tests also pick out those pregnancies at higher risk that requires more closely monitoring e.g., pre-eclampsia to prevent an adverse outcome.
Invasive prenatal tests like amniocentesis or chorionic villus sampling are diagnostic tests. They require the doctor to put a needle into the womb to collect an amnio fluid sample that can increase the risk of miscarriage.
When is prenatal screening tests performed?
Pregnancy disorders and complications are poorly predicted by traditional risk factors, e.g., maternal history and previous pregnancies, alone. Ideally all pregnant women of all ages should be offered the opportunity for prenatal screening in the first trimester.
By combining maternal age with biomarker testing and ultrasound information using risk calculation software, complications in pregnancy can be detected early and it also reduces unnecessary invasive tests.
For people with a high chance of chromosol abnormalities, screening is complete and the parents are offered prenatal diagnosis (invasive testing). When the chance of chromosol abnormalities is very low, screening is also complete; the results don’t suggest prenatal diagnosis is needed. However, if the risk is intermediate, extra blood tests are done in the second trimester to better predict the chance of chromosol abnormalities or the parents can opt to perform prenatal cell-free DNA (cfDNA) screening (NIPT).
If I decide to do a cell-free DNA (cfDNA) screening or NIPTin the first trimester, should I still ask my doctor to perform biomarker blood testing or not?
During prenatal cell-free DNA screening, DNA from the mother and fetus is extracted from a maternal blood sample to determine the chance of chromosomal abnormalities such as Down syndrome, trisomy 13 and trisomy 18. This screening can also provide information about fetal sex and rhesus (Rh) blood type.
In addition to determine the risk of chromosomal abnormalities, Biomarkers can be used to screen for other conditions, such as pre-eclampsia, fetal growth restriction and preterm birth. By performing biomarker testing in the first trimester the following information can be obtained:
- Gestational diabetes
- Preterm delivery
- Open spina bifida
- Major cardiac defects
- Small for gestational age
- Trisomy 21, 18 and 13