An embryo, not a parasite

It even sounds really ridiculous and unworthy to compare a human embryo with a parasite. But since some ideological movements have lately called the embryo a “parasite” that lives at the expense of the woman’s body, let’s clarify the issue.

We all know that white blood cells are a special type of blood cell that protects us from infections (bacteria, viruses, and parasites). If the embryo were just a parasite, the woman’s immune system would attack and reject it as it does any parasite. But what happens instead?

The first day after implantation, a special kind of white blood cell is rapidly recruited to the uterus and activated: “Tregs.” These white blood cells are regulatory immune cells, which allow the embryo to not be rejected by the maternal immune system, despite being genetically different from her due to the paternal genes present in the embryo. This mechanism has been deeply studied in detail by multiple scientists around the globe.

Not only do these cells protect the fetus during pregnancy, but the uterus also cyclically prepares itself for pregnancy, accumulating these protective cells each month following the hormonal changes associated with the female period. Even more, these regulatory cells are temporarily recruited to the uterus after intercourse, just in case it could lead to pregnancy.

We can also consider cases when patients need an organ transplant; a medical intervention is necessary to suppress the immune system so the received organ is not rejected. This highlights that no medical intervention is needed on the woman’s immune system to produce maternal-fetal tolerance, because the embryo is not a “strange organ,” but someone whom the mother’s body is prepared to receive.

To summarize, completely different from what happens during a parasitic infection, during pregnancy the human immune system mounts a complex mechanism that prepares the uterus under hormonal control, ensures the maintenance of immune tolerance to the fetus, and allows “vascularization to guarantee a steady supply of nutrients and oxygen to the fetus for proper growth and development” (Ruocco, 2014).