The highest sensitivity detection rate (DR) of the current first trimester prenatal screening (biophysical and biochemical parameters) is claimed to be between 75%and9090% with a false positive rate (FPR) of 3-5% [ 1, 2].
The rationale behind such a proposed paradigm shift is the observation that it may be possible to extend the scope of the current first trimester integrated or combined test, conducted at 11 13 weeks of gestation, to detect not only fetal chromosomal anomalies, but also pregnancies at risk for an array of complications including PE, IUGR and PTL [1,2].
Study Design: A decision tree was designed that compared four possible screens for Down syndrome: (1) current second-trimester expanded maternal serum α-fetoprotein test (AFP), (2) first-trimester nuchal translucency screen, (3) first-trimester serum screen, and (4) combined first-trimester screen with both nuchal translucency screen and a serum screen.
However, there is growing evidence that comparably good results can also be achieved in general obstetrical populations, making NIPT an alternative to current first-trimester screening protocols.
It now remains to explore how useful these potential biomarkers will be in increasing the detection rate of the current first-trimester screen.
Although 10 times better than the PPV of current first-trimester screening in a similar population (as reported in the same study), this is still far below the near 100% required for a diagnosis of trisomy 21.
In the current setting, third-trimester pregnant women were enrolled since pregnancy specific changes, such as GDM, had become manifested and were being diagnosed by that time.
Regarding maternal behavior, 32% smoked in the last trimester of current pregnancy.
A questionnaire was administered during the 28th gestational week, asking about lifetime, pre-pregnancy, first trimester and current smoking quantity.
