December 6, 2013. Marta Wegorzewska, PhD candidate.

We learned in a prior post that fetal DNA can be found in the mother’s blood. Companies are using this finding to create new prenatal screening tests. This finding also raises some interesting questions we will examine in a two-part series.

How does fetal DNA get into the mother’s blood?

I spent a lot of time during my PhD thinking about how this could happen! Let’s tap into the mind of a scientist….

Maybe the answer lies in the placenta.

The placenta is a unique organ. Like the stomach, it is a sac. It doesn’t hold food, however, but blood. Only women can have a placenta, but they are not born with one. A placenta is made with each new pregnancy and is discarded after nine months. The placenta supports the growing fetus’ nutritional needs. It provides the fetus with oxygen and disposes of waste.

Maternal and fetal blood fills up compartments of the placenta. These compartments come into close contact at the maternal-fetal interface.1

Three layers separate the maternal blood from the fetal blood at the interface. Nutrients (iron), gases (O2 and CO2) and waste can freely pass between the mother and the fetus through the three layers.

Scientists thought the placenta was a perfect physical barrier preventing blood from the mother and the fetus from mixing. The discovery that fetal DNA floats in the mother’s blood raises the question: can fetal cells cross the three layers of the placenta?

Or maybe fetal cells fall off the placenta and into the mother’s blood. The three layers are fetal in origin. They come into direct contact with the mother’s blood. If cells shed from layer one, they will fall directly into the mother’s blood.2

And there are more possibilities! Only time will tell as scientists work to figure out the answer.

This work is funded in part by the Graduate Student Internships for Career Exploration (GSICE) program at UCSF

This post is checked by the following science articles:

1. Maltepe, E., Bakardjiev, A.I., and Fisher, S.J. 2010. The placenta: transcriptional, epigenetic, and physiological integration during development. J Clin Invest 120: 1016-25.

2. Bianchi DW. 2004. Circulating fetal DNA: its origin and diagnostic potential-a review. Placenta Suppl A:S93-S101.


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