Cell-free fetal DNA screening
Autoimmune disorders may be the cause of test failure
Posted By Braverman IVF & Reproductive Immunology | 17-December-2018
A recent review published in the Journal of Translational Medicine showed a strong association between maternal autoimmune diseases and the failure of cell-free fetal DNA screening (cffDNA).
While some publications suggest that patients who receive a ‘no call’ result are at increased risk for aneuploidy, this recent study suggest that non-informative results may be caused by underlying autoimmune diseases and does not place your pregnancy at higher risk for aneuploidies.
We will take this opportunity to explain you what parameters including maternal autoimmune disorders may influence non-informative results for this test.
1.What is a cell-free fetal DNA test?
A cell-free fetal DNA prenatal test, also known as a non-invasive prenatal screening (NIPS) isolates cell-free fetal DNA from the pregnant woman's blood to test for trisomies of chromosomes 21, 18 and 13 and sex chromosome aneuploidies in the fetus during the first trimester.
Cell-free fetal DNA (cffDNA) is genetic material that is released by the placenta and circulates in a woman's blood during pregnancy (1).
The fetal fraction, which is the percentage of cell free DNA of fetal origin, starts increasing at 10 weeks of pregnancy and continues to increase with advancing gestational age (1).
The fetal fraction exceeds 4% in most pregnant women which is the usual cut-off for
decision making (2).
However, for some patients, results are not reported because of low fetal fraction (4%) which is the main cause of non-informative results (3-4). The rate of test failure has recently been estimated to 4% (5).
2- What parameters can cause a cell-free fetal DNA test to fail?
The test is done too early:
In a study (6), they found that the failure rate was increased when done too early:
27.4% of failure when the test was done at 9 weeks
12.0% between 9.0 and 9.9 weeks
5.9% when done after 10 weeks
Interestingly, another study did not find an association between test failure and gestational age in 18 510 women between 10- and 14-weeks’ gestation (7).
In most cases, cffDNA tests have been validated on singleton pregnancies only.
Although some laboratories will report results on cffDNA screening tests performed on twin pregnancies, ACOG (The American College of Obstetricians and Gynecologists) and SMFM (The Society for Maternal-Fetal Medicine) do not recommend the use of cffDNA screening in multiple gestations until larger prospective studies are done to establish the test’s accuracy for multiple pregnancies.
Having a high BMI can also be a cause of test failure as reported in various studies (8-10). Indeed, higher levels of cell free DNA of maternal origin have been reported in obese patients (11) which decrease the fetal fraction (as cell free DNA levels of fetal origin remain unchanged). These increased levels of cfDNA of maternal origin may be due to a higher turn over of cells from white adipose tissue.
A study (6) found that the aneuploidy incidence was increased (23.3%) in samples that did not return a result when compared with the aneuploidy incidence in samples with a cffDNA testing result (10.9%, p=0.004: a low p value means that the results are highly significant).
Similar findings were reported, with a significantly decreased fetal fraction being found in pregnancy affected by trisomy 18, trisomy 13, monosomy X, and triploidy (12).
3- Autoimmune disorders can also be a cause for a fetal DNA test failure!
In a recent study, that included N=9867 singleton pregnancies, 0.59% of the tests were not reportable. Besides BMI, another parameter could explain these “no call” results: the presence of an autoimmune condition.
Indeed, 12.1%in the group of patients with a non-reportable cfDNA result had an autoimmune disorder prior to the pregnancy, compared with only 1.7% patients with a successful assay.
So, your risk for having a non-reportable test result is multiplied by a factor 10 if you have an autoimmune disorder!
One possible explanation, in patients affected by SLE (Systemic Lupus Erythematosus), higher levels of serum total DNA were found in maternal serum which could lead to a low fetal fraction (13-14) and result in a test failure.
Another important point to highlight is the use of immune therapies. Some immune therapies such as anti-coagulant may reduce trophoblast apoptosis (15) and enhance trophoblast survival (less cell free DNA of fetal origin), which may result in a low fetal fraction and test failure (16-18).
G-CSF therapy may also alter cell free DNA of maternal origin by promoting a natural process NETosis (19), naturally increasing during pregnancy (20).
Cell free fetal DNA screening has been developed and validated in a mostly healthy population and on singleton pregnancy. Having received a ‘no call’ result does not place you automatically at higher pregnancy risk for aneuploidy especially if you have a high BMI or if you have an autoimmune disorder.