There are certain phases of a woman’s life in which having a reduction in circulating platelets, even a slight one, is normal, such as before the menstrual cycle or during pregnancy.
Platelets – or thrombocytes – are disc-shaped fragments of cytoplasm produced by the marrow, which play a key role in blood clotting and are distributed in our body to prevent excessive bleeding and hemorrhage.
When the amount of platelets in the blood is lower than normal, we talk about plateletopenia (or thrombocytopenia), which causes an increased risk of bleeding.
A CBC, an important blood test in pregnancy, is required to measure and monitor normal platelet levels.
What does this test consist of, and what are the optimal parameters?
Platelets: why do they decrease during pregnancy?
Thrombocytopenia manifests itself with insufficient circulating platelets in the bloodstream – between 150,000 and 450,000/microliter.
In most uncomplicated pregnancies, the platelet count is reduced by 15-20%, and even more in twin pregnancies. Thrombocytopenia in pregnancy, called gestational thrombocytopenia, is usually a condition that does not endanger the health of the woman or the fetus.
It usually occurs as gestation progresses, particularly after the second trimester, and then resolves spontaneously after delivery, within 7 weeks tops. It is, however, very rare in the first trimester.
The platelet count generally accounts for around 80,000\microliter. The mechanism(s) of gestational thrombocytopenia is not known. Still, we can assume it is related to increased plasma volume during pregnancy, increased platelet clearance, or platelet sequestration in the placenta or spleen.
Gestational thrombocytopenia does not increase the risk of bleeding, which is why no specific treatment is needed during delivery, and it does not increase the risk of platelet clearance at birth in the newborn.
Plateletopenia: Monitoring before and during pregnancy
Before conception, but not always available, platelet counts in pregnancy are performed by a CBC from venous blood sampling. All pregnant women should have a blood test to monitor hemoglobin levels and platelet counts. In women who have had mild thrombocytopenia during a previous pregnancy, monitoring should be more frequent because this increases the risk of plateletopenia in a subsequent pregnancy 14-fold.
Gestational thrombocytopenia is a para-physiological condition that does not require treatment. In fact, platelet counts usually exceed 75000/MCL. However, this can cause minor but repeated bleeding, such as episodes of epistaxis, which can contribute to iron deficiency anemia.
Before and during pregnancy, monitoring makes it possible to assess possible risks, arrange treatment only in rare cases when necessary, and keep the patient under control to avoid complications.
In cases where the thrombocytopenia is particularly severe, with platelet counts below 75,000/microL, it is most likely not gestational thrombocytopenia but thrombocytopenia associated with other diseases.
Plateletopenia in pregnancy: Causes
There can be several causes behind reduced blood platelet levels. If plateletopenia occurs in the first trimester, it could be an autoimmune form, immune thrombocytopenia (ITP). In this case, autoantibodies cause platelet destruction. ITP may be present before pregnancy or at any stage of pregnancy or postpartum and may be associated with plateletopenia in the newborn.
More rarely, plateletopenia arising in the first trimester may be related to other conditions such as hemolytic uremic syndrome or thrombotic purpura, thrombocytopenia, or other hematologic diseases.
When severe thrombocytopenia occurs in the third trimester of pregnancy, the most common cause is preeclampsia, which in the most severe forms is called HELLP syndrome. Preeclampsia is a condition that causes hypertension, proteinuria, and severe plateletopenia, and it usually resolves after delivery.
However, other types of plateletopenia may be present even before pregnancy or develop during gestation.
