If you’ve been told that you’re at risk of fetal and neonatal alloimmune thrombocytopenia (FNAIT) after one or more previous pregnancies weren’t affected by the disease, you may be wondering how this is possible.
To understand why FNAIT can occur even after a non-affected pregnancy, it is important to grasp how the mother’s immune system can be triggered to develop antibodies that attack the platelets of the fetus and cause harm.
Understanding sensitizing events
Let’s explore how the condition known as FNAIT arises in the first place. FNAIT is always caused when the mother’s blood lacks a specific human platelet antigen (HPA) that the father has. The fetus then inherits this from the father. When the fetal platelets with the father’s HPA come into contact with the maternal circulation, the maternal immune system mounts a response and produces anti-HPA antibodies.
This encounter is known as a sensitizing event. This may happen in a pregnancy in which the fetal platelets come into contact with the maternal circulation. Typically, the fetal and maternal blood do not mix. However, any breakdown in the placental barrier can create an opportunity for the two to come into contact, triggering a sensitizing event.
Read more about FNAIT testing and diagnosis
Sometimes, tiny leaks of the fetal blood can cross the placenta into the maternal circulation. Certain medical procedures, such as the extraction of fetal cells for testing, can result in injury that causes the blood to mix. Certain pregnancy complications, such as vaginal bleeding or a miscarriage, can also create an opportunity for fetal platelets to come into contact with the maternal circulation.
The point is that this event can occur after a previously healthy pregnancy, causing FNAIT to arise in subsequent pregnancies despite a clean medical history.
Important next steps
It is difficult to predict when a sensitizing event will take place. Platelet antigen genotyping, which can identify if HPA incompatibility is a possibility, is not routinely carried out—keep in mind that FNAIT is a rare disorder. Typically, the risk of FNAIT is only identified if there is evidence that a child from a previous pregnancy had explained signs of bleeding from birth that could point to a lack of platelets.
Nevertheless, once the risk of FNAIT has been identified, your OB-GYN will keep a close eye on your health and that of your baby throughout pregnancy. This will allow them to initiate therapies that can alleviate the risk of complications to your child.
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