books, history

Would this Kill Me in the 1800s: Rh Factor

You may remember an embarrassingly long time ago, I took a poll on Twitter to see what you guys wanted to be the subject of my next WtKM1800s post to be. The winner was Rh factor. I’m sorry it’s taken so long for me to get to this point, but here we are at last.

What is it?

Rh factor is short for Rhesus factor, which refers to a protein found on the red blood cells of roughly 85% of the human population. It’s a harmless protein and having (or not having) it doesn’t affect your appearance, health, behavior, or life expectancy in any way. In fact I couldn’t even figure out what exactly this protein is supposed to do in my research. I guess it just sits there, as far as we know.

There is one set of circumstances, however, when it can cause a problem.

If a pregnant woman is Rh negative (ie. missing the protein) but her baby isn’t, then the baby’s life could be at risk.

Where does the danger come from?

Usually during pregnancy, the mother’s blood doesn’t mix with that of the fetus, but sometimes this can happen–say if she has a miscarriage or some kind of trauma. It’s also possible during some tests (like amniocentesis).

When this happens, the mother’s body sees the Rhesus protein as a foreign invader, like a virus or bacteria, and sends out white blood cells to destroy it. When the immune system attacks an invader, it creates antibodies. Antibodies are special cells “programmed” to attack a specific bacteria, virus, or protein.

In this case, they attack the fetus’s red blood cells, which can lead to anemia, especially in subsequent pregnancies. This form of anemia, hemolytic anemia, can be severe and life threatening.

In most cases, the mother’s life is not at risk, unless there are other complications present.

Today, this is prevented through pre-natal blood tests. If a mother is Rh negative, her doctor will check to see if the baby is Rh positive. If it is, then the mother will receive injections of Rho(D) immunoglobulin to prevent her body from making the antibodies. She’ll also receive another injection when she gives birth, just to protect her from post-natal complications and to (hopefully) prevent her from developing antibodies if her next pregnancy is Rh positive.


The Rh factor wasn’t discovered until the 1930s. A similar protein was first discovered in the blood of Rhesus monkeys (hence the name), but it’s significance wasn’t discovered until a decade later when scientists mixed Rhesus blood with blood from rabbits.

The first experimental serums were developed shortly thereafter, but it wasn’t until the 1960s that it went into common medical use (see the Columbia article below for more information).

Lost Stories

It’s hard to even calculate how many deaths would have been caused by Rh incompatibility prior to the 1960s (if you can do that kind of math, you have my sincere admiration).

Prior to its discovery and the ability to diagnose the incompatibility, the infant deaths would have been chalked up to bad luck or bad air. The sad fact is that babies frequently died at or just after birth, and many women had miscarriages for many reasons, including malnutrition, complications from other illnesses, hard labor, and injuries. A dead baby was a dead baby, regardless of the reason. In some Victorian-era societies, murdering a baby wasn’t even considered a crime because so few of them survived anyway and it was impossible to prove.

A relatively safe theory is that when a woman had one healthy child, followed by several miscarriages or children who died shortly after birth, there would be a higher likelihood of Rh incompatibility, but we’ll never know for sure. Some of the children may have even survived, albeit sickly and disabled as treatments for anemia were limited. But that, I think, is a subject for a different blog post.


Rh factor article from the Mayo Clinic
Cleveland Clinic article on Rh factor 
Rho(D) Immuneglobulin wiki 
Pregnancy Complications: Rh Factor 
Wiki on Rh factor
RhoGAM development and history
The Invention of Murder by Judith Flanders

Like what you see? Join my Patreon to get early access to WtKM1800s posts, to vote on future tops, and more!