Written by Clay Smith
There is a normal drop in platelet count during pregnancy. In the first trimester, the normal count is around 250,000 and decreases to about 225,000 at delivery. Platelet counts <100,000 were rarely encountered in normal, uncomplicated pregnancies and should not generally be considered a physiologic change.
Why does this matter?
Pregnancy causes lots of physiologic changes. Heart rate increases. BP decreases. Blood volume increases. Hematocrit decreases. Prior reports note that gestational thrombocytopenia is expected. But what is the expected drop in the platelet count?
Watch for falling platelets
This was a study of about 4500 women with uncomplicated pregnancies. During the first trimester, the platelet count was 251,000, compared to 273,000 in non-pregnant women. At delivery, the platelet count was down to about 225,000. See figure. Only 9.9% had platelet counts below 150,000 and just 1% were below 100,000. In most cases with a platelet count <100,000, this was an indication of another cause and was not simply a physiologic change of pregnancy.