I remember 15 years ago, my colleagues and I in high risk obstetrics were discussing the future possibility of analyzing fetal cells in maternal blood.  Back then, the task seemed daunting since there was little knowledge regarding how to identify the fetal cells from the mother's blood, but we did know that every pregnant patient had circulating fetal cells in her system, due to the vasculature of the placenta, which allows fetal cells to penetrate into the maternal side.

We discussed this issue because we hoped, by identifying the fetal cells, we might be able to recognize chromosomal abnormalities from the maternal blood.  However, the science at that time was limited.

As time passed, alternative tests were developed such as the nuchal translucency (NT) test. This test uses an ultrasound to measure the fetal neck, as well as measuring certain chemicals in the maternal blood.