Essential thrombocythemia is a Myeloproliferative Neoplasm Syndrome (MPN) condition, characterized by an overproduction of platelets (thrombocytosis) by mature megakaryocytes in the bone marrow (hyperplasia). It's the most common type of MPN. Two to three people in every 100,000 are diagnosed with MPN every year.
Normally, values higher than 600,000 platelets/ml determine the diagnosis. Currently, this limit has been lowered to 400,000 platelets/ml, though.
Although this alteration is more common in middle-high aged people, 15-20% of patients are less than 40 years old. There's a second peak of incidence in patients aged 30, especially women. For this reason, the effect this disease may have on pregnancy is studied.
Its clinical manifestation is based on a higher tendency to develop thrombotic complications and/or bleedings, which can be dangerous to non-treated patients.
The main symptoms of essential thrombocythemia are:
- Transient and functional microcirculation disturbances (vasomotor disturbance)
- Trombotic complications
- Hemorrhagic symptoms
Generally, one of the symptoms is predominant. However, two complications can be produced at the same time or sequentially. Only a small percentage of patients suffer from serious and threatening complications. Most patients are asymptomatic or suffer from alterations without serious consequences.
There's no correlation between haemostatic complications and the thrombocytosis levels. In fact, there are patients with normal platelets levels who present, more or less serious, thrombohemorrhagic complications.
The main objective of essential thrombocythemia treatments is to keep the number of platelets inside the normal range, that is to say, under 400,000 platelets/ml. Once treatment begins, not exempt from side effects, it should be maintained for years until its goal is achieved.
The most used treatments are: alkylating agents, hydroxyurea, anagrelide, interferon or antiplatelets like aspirin.
How does it affect pregnancy?
There are cases in which the diagnosis was known before pregnancy. Other patients discover their condition after routine blood tests during pregnancy.
Pregnancy doesn't pose an added danger to essential thrombocythemia because, when the disease affects young women, its development is usually benign. Although pregnancy does not aggravate the disease, there's an adverse risk, that is to say, pregnancy negatively affects essential thrombocythemia.
Thrombocythemia during pregnancy is associated with placental vessels thrombosis and it can produce multiple infarcts and secondary placental insufficiency. This last one carries a risk of miscarriage during the first semester of gestation of 37% to 53%. The risk of miscarriage in the general population is around 15%. In addition, there may be increased risks of fetal growth retardation.
Other consequences associated with this pathology are placental detachment, preeclampsia, and intrauterine fetal death.
It is important to mention that there is no direct correlation between the consequences of the disease during pregnancy and the mother's platelets values.
Although controversial, according to several retrospective studies, the chances of carrying a baby to term are increased in women who have taken aspirin.
The most effective and recommended treatment for pregnant women with thrombocythemia, who require myelosuppression, is interferon alfa because it has no teratogenic risk. However, the experience of its use during pregnancy is reduced.
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