Yes. In over 95% of cases of Down syndrome there is no family history of this condition. The same can be said for trisomy 13, trisomy 18, Turner syndrome, and Klinefelter syndrome. Therefore, not having a family history of one of these conditions does not decrease your risk for these conditions below your age related risk in pregnancy.
Similarly, having just one affected relative with one of these conditions does not significantly increase your risk, since that condition was likely new to that person in your family and not inherited. However, having two or more relatives with same chromosome condition may imply an increased risk for that condition.
No. The sensitivity and specificity refer to the ability of the test to accurately call a negative result negative, or a positive result positive. If you’re screening result is “positive” (remember, this is not a diagnosis), the risk is based on your age and the specific condition. This is because the risk for many of the conditions screened for by NIPS increases each year as a woman ages. So as a woman ages, it is more likely for a positive to be a true positive.
For example, a 21-year-old woman who has a “positive” NIPS for trisomy 13 actually has just a 6% risk that the pregnancy is actually affected. This is because trisomy 13 is a rare condition, NIPS is not as accurate for trisomy 13 as other conditions, and because of her age, her starting risk was very low.
A 35-year-old woman who has a “positive” NIPS for Down syndrome however, has a 79% chance that the condition is actually present, because her starting risk based on her age was higher, NIPS is most accurate at screening for Down syndrome, and Down syndrome is more common in the general population.
Expanded NIPS refers to NIPS screening tests that look for abnormalities in chromosomes other than 21, 18, 13, X and Y.
The accuracy of looking for conditions beyond the standard panel drops significantly. However, it may be useful in a situation where there are differences on an ultrasound that are suggestive of a genetic condition and the mother declines diagnostic testing such as an amniocentesis.
One of the things an expanded NIPS test may look for are microdeletions or small missing pieces of chromosomes. Most of these conditions have a positive predictive value of less than 1%. This means that even if you tested “positive” for a microdeletion on NIPS, your risk may be less than 1% to actually have a child with that condition.
NIPS is a rapidly growing field. However, the accuracy of these new platforms is not yet well understood. Therefore, it is currently recommended that women interested in pursuing NIPS for screening early in pregnancy have the traditional NIPS panel.
NIPS is a screening test to determine if a pregnancy may be at an increased risk for a particular condition, so the family may decide if they would like
to pursue further testing during their pregnancy.
It looks at small pieces of chromosome material released by the placenta into the mother’s blood stream. This test screens chromosomes 21, 18, 13, X and
Y for extra or missing copies. The most common conditions screened for are trisomy 21 (Down syndrome), trisomy 18, trisomy 13, Turner syndrome (monosomy
X), Klinefelter syndrome (XXY), and triple X syndrome.
This test will either come back with an increased risk for one of these conditions, or will come back with a decreased risk for all conditions screened
for, which is a risk of 1 in 10,000. This screening test can detect approximately 99.2% of cases of Down syndrome, and over 95% of cases of trisomy
18 and 13. However, it is just a screening test and cannot diagnose or rule out any of these conditions in a pregnancy.
A screening test (NIPS, first trimester screening, maternal serum screening) adjusts a woman’s risk to have a pregnancy affected with a specific condition based on certain factors. The result will either increase or decrease the risk for those specific conditions.
A diagnostic test looks directly at the baby’s genetic information to give a yes or no answer as to whether or not a baby is affected by a specific condition. A diagnostic test is the only way to know for sure whether or not a baby is affected during a pregnancy. However, starting with a screening test may help a woman decide if a diagnostic test during a pregnancy is necessary.