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Pathophysiology of preeclampsia
The cause and pathophysiology of preeclampsia remains unclear but is likely to involve abnormal placentation changes during the late first and second trimester and/or an abnormal maternal immune response to the pregnancy.
In normal pregnancy the maternal spiral arteries undergo changes (remodelling) so they dilate and their walls become very thin allowing a high flow of blood (low resistance circuit) from mother to fetus so efficient gaseous and nutrient exchange can occur. As this model below shows the spiral arteries in preeclampsia do not look the same as in normal pregnancy. The spiral arteries have defective invasion into the placental space and abnormal remodelling of the spiral arteries means there is still high resistance and low flow of blood. This results placental ischaemia and reduced placental perfusion.
This placental ischaemia then results in endothelial cell dysfunction on the maternal side causing release of vasoactive substances, such as s-Flt, into the maternal circulation leading to vasoconstriction, hypertension, and capillary leakage. Release of these substances into the maternal circulation has distant effects on a number or organs including activation of the coagulation system with platelet aggregation. Reduced placental perfusion may also have effects on fetal growth and wellbeing causing intrauterine growth restriction (IUGR) also known as small for gestational age (SGA).
Activity. Maternal features of severe preeclampsia. What are the possible clinical features in the mother?
Hypertension is the most common feature of preeclampsia. Have a think about what other organs may become involved and how this would present for women as signs and symptoms of the disease? Jot these down on the notepad and then check with the slide belo
When you have done that
click here to check with this slide - SLIDE 2
Which organ system do you think is most commonly involved with preeclampsia?
It is the kidney. Renal involvement usually presents as proteinuria (≥2+, protein creatinine ration (PCR) >30 or >0.3g/24hr). The vast majority of women with preeclampsia will have significant proteinuria, however this is not an absolute requirement for diagnosis and a few cases of atypical preeclampsia may present with hypertension and features of other organ disease.
We have talked about placental ischaemia and reduced placental perfusion happening in preeclampsia - this may lead to placental abruption. But more commonly it will lead to effects on the fetus such as fetal growth restriction. This may result in the baby being delivered small for gestational (SGA), hypoxia and/or cause acute fetal distress
