Preeclampsia is a serious blood pressure disorder that can affect all organs in a pregnant person's body. It typically starts after the 20-week mark of pregnancy, but in most cases it happens much later, and closer to term. It usually presents with high blood pressure (above 140/90) and one or more other symptoms that signal that your organs are being affected, like protein in your urine, low platelets, high liver enzymes, or others.
Why does preeclampsia happen?
When a baby implants into the mother's uterus and starts to grow the placenta, the placenta has to implant into the mother's body and work with her immune system. Her immune system needs to accept the placenta and allow it to dig in and develop its blood supply that will nourish the baby. When the placenta conflicts with the mother's immune system, it implants shallowly. So then, later on in the pregnancy, it cannot draw nutrients across the baby properly, and so it sends out signal proteins into the mother's body, which raise her blood pressure and which mess with her organs and cause the other symptoms of preeclampsia, such as protein in the urine.
Now, the question becomes: what caused that immune conflict? Sometimes it is due to underlying conditions, like pre-existing chronic hypertension. Sometimes it is due to the mother's genes just not playing well with the father's genes and her body not recognizing his DNA well in order to build a good placenta together. Sometimes it is due to a problem with the baby. Sometimes it is a roll of the genetic dice that means the placenta just doesn't work as well as it should. It can be kind of tricky to determine what things might be a factor in any particular case, so if you have questions about what happened to you or your likelihood of recurrence, your OB or MFM would be a good person to talk to.
Are there different kinds of preeclampsia?
Below you will find some definitions for different types of hypertensive disorders of pregnancy. The term "preeclampsia" can be an umbrella term for all of these. It's important to know that the "pre" in "preeclampsia" means "before delivery", but what it really means is "before a seizure".
New onset of high blood pressure and, at least, one other diagnostic symptom from 20 weeks gestation up through delivery of the baby.
Postpartum HELLP Syndrome
Each of these onsets is the same umbrella disorder with different types of presentation. Researchers are looking at this disorder from a molecular level, and no doubt, we will start to learn more about early vs. term onset.
If you want to know more, you can visit this page from the American College of Obstetricians and Gynecologists (ACOG) on preeclampsia high blood pressure during pregnancy.