Non-invasive prenatal screening (NIPS): What patients need to know when being counseled about NIPS
Welcome to Part 3 of our blog series on how non-invasive prenatal screening (NIPS) has changed the world of prenatal screening. This installment will focus on what patients need to know when being counseled about NIPS by their healthcare provider.
What do patients need to know when being counseled about the option of NIPS?
How many patients have gone into their doctor’s office and asked for “the gender test”, without realizing that what they were actually asking for was an NIPS screening test? In a way, it is wonderful that knowledge of the baby’s gender is their biggest concern at that stage. That said, each patient should receive education and counseling to ensure adequate informed consent for NIPS so that they are aware of the risks in their pregnancy, the possible results that can be received from NIPS, and the available follow up options should they receive an abnormal or inconclusive result.
What does NIPS test for?
Core trisomies: All NIPS tests screen for trisomy 21, trisomy 18, and trisomy 13. While the majority of healthcare providers do not have the time to go into great detail about each core trisomy, microdeletion and possible sex chromosome abnormality that could be detected, the patient must be educated about the types of conditions that may be detected and the types that will not be detected by this testing. For example, a single gene disorder like sickle cell anemia or cystic fibrosis will not be detected through NIPS. It is therefore very important to take a detailed family history from the patient (if not already completed), to rule out the need for carrier screening or possibly invasive testing.
Microdeletions: Healthcare providers must be aware of the capabilities of the laboratory to which they are sending each NIPS sample. Do they offer microdeletion testing? If so, is it part of the basic test or does the healthcare provider need to request it, or opt-out of reporting results on microdeletions? The patient needs to be aware AND may need to decide on whether to add microdeletion testing or opt-out.
Gender: While this may be a primary reason some pregnant women pursue NIPS, the screening test may result in an inconclusive, or an incorrect answer. The screening may indicate male, and a female may be noted by ultrasound later in the pregnancy, or vice-versa. The possible reasons for the discrepancy are many: from a mislabeled sample, to an early twin demise, to a biological cause that may only be diagnosed after birth.
Sex chromosome anomalies (including 45,X, 47,XXX, 47,XXY and 47,XYY, and others): The finding of an extra X chromosome may complicate an accurate call for the fetus. Maternal X chromosome abnormalities may be suspected from an NIPS result, leading to direct testing of maternal (not fetal) DNA. Genetic counseling for sex chromosome anomalies may be a challenge for many reasons, one of which being that patients often aren’t expecting them.
How accurate are the test results?
Each woman must understand that NIPS is a screening test. It has a much lower false-positive rate and a higher detection rate than traditional maternal serum screening. That said, it is a screen based upon testing cell-free DNA from the placenta. Find further details in our previous blogs regarding how NIPS is different from maternal serum screening, and unanticipated test results that may be received from NIPS. A positive or inconclusive screening result should be followed up by more invasive testing if the parents wish to confirm or rule out a diagnosis. A negative result should be reassuring, but it is possible that some trisomies, microdeletions, and other chromosomal anomalies may be missed.
What about receiving no, or partial test results?
There are many reasons why an NIPS test may fail to provide results. These include low Fetal Fraction (the percentage of cell-free DNA in the mother’s blood sample), multiple unusual results found across the genome, maternal malignancy, maternal microdeletions, and maternal sex chromosome anomalies. Sometimes these results may be explained by further testing, while at other times, the reasons remain unclear.
When is NIPS performed?
For most testing laboratories, NIPS may be submitted as early as 10 weeks gestation, with no upper limit on testing. The education of the patient should include details related to her gestational age at the time of screening. For example, a woman may have many follow up options if she gets results at 11 weeks, compared to receiving results at 22 weeks. Her decisions may also differ depending upon her gestational age.
Does your patient want to know this information about her pregnancy?
Screening for chromosomal abnormalities is not desired by everyone. It is important to explore each patient’s values and needs during her pregnancy. After education and counseling, patients should know that they have the option to decline all screening and diagnostic testing in their pregnancy.¹
What testing may be available for confirmation?
It is important to have a short discussion regarding possible follow up testing that may be considered for a positive or inconclusive NIPS result. These may include chorionic villus sampling (CVS), amniocentesis, ultrasound, maternal blood studies, fetal microarray testing, or further testing on the baby after birth.
In the end, all patients should be educated about screening and diagnostic testing during pregnancy. Each woman, or couple, then needs to determine if they want to know the information the screening test will provide to them and if the risks are worth taking. While no one can be prepared for every possible result, having a basic knowledge of NIPS testing will help patients to move forward with making the best decisions for themselves after receipt of the test results.
References:
1. Prenatal Cell-Free DNA Screening Statement, https://www.nsgc.org/p/bl/et/blogaid=805, updated April 12, 2018.
Joy Redman, MS, CGC, MBA
Joy is a Trusted Advisor for Metis Genetics. She is a board-certified genetic counselor with a long time interest in the translation of genetic information between the laboratory and healthcare providers. She has practiced clinically in both the prenatal and ophthalmology settings; educating patients about the risks and benefits of genetic testing to help them make decisions regarding their own healthcare. She has worked in a variety of laboratory settings; each one focusing on education about genetic test offerings as the field has evolved so that clinicians are able to provide the best testing options to each patient.
