Neonatal alloimmune thrombocytopenia (NAIT) is a disorder that affects pregnant people and their fetuses. It occurs when the birthing parent’s immune system produces antibodies that attack and destroy the fetuses’ platelets.

Platelets are responsible for blood clotting, and when their count becomes too low, it can lead to bleeding in the baby’s brain or other organs. Doctors may only detect the condition after birth when the baby shows signs of bleeding or bruising.

Health experts do not fully comprehend the exact cause of NAIT. However, some experts believe it happens when there is a mismatch of certain blood proteins between the birthing parent and the fetus.

This article explores NAIT, its symptoms, causes, diagnosis, and treatment.

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NAIT is a rare disorder that affects fetuses or newborns, and experts estimate that it only occurs in 1 out of every 1,000 births. Doctors may also refer to the condition as fetal neonatal alloimmune thrombocytopenia (FNAIT).

It is a serious condition that can lead to severe bleeding in the fetus or newborn. Medical literature from 1953 described the first case of NAIT. Its symptoms can depend on how low the platelet count drops.

Typically, NAIT occurs when the immune cells in the birth parent’s bloodstream identify the platelets from the baby as foreign and begin attacking them. Having a low platelet count can be harmful to the infant.

For the birth parent, NAIT can occur during their first pregnancy, in later pregnancies, or both.

Learn more about low platelet counts, or thrombocytopenia.

Symptoms may either occur before birth or up to 4 weeks after. The most common symptom of NAIT is bruising, or petechiae, which are small red or purple spots on the skin.

However, the spectrum of disease ranges from mild to moderate thrombocytopenia, which refers to a low platelet count, to more severe. Most with the disease will experience mild symptoms.

Bleeding in major organs — including the lungs, brain, eyes, and heart — can also occur in more severe cases. Catastrophic intracranial hemorrhage is the medical term for bleeding in the brain. Severe cases of NAIT can be fatal or lead to lifelong disability.

Platelets have proteins on their surface called human platelet antigens (HPAs). A fetus will inherit half of their antigens from each biological parent. During pregnancy, these platelets can cross into the maternal bloodstream, which generally causes no problems.

However, in NAIT, the maternal immune system does not recognize the baby’s paternal HPAs and develops antibodies. The antibodies then cross the placenta and target the fetus’s platelets. These antibodies are called anti-HPAs. Anti-HPA-1a is the most common HPA, but other types do exist.

These antibodies are responsible for platelet destruction in the fetus or newborn.

Doctors can find NAIT challenging to diagnose, especially as it may involve detecting rare antiplatelet antibodies.

There is no routine blood test to see if a birthing parent has antibodies to platelets. Therefore, many people do not know they are at risk of having a pregnancy involving this condition until they give birth to a baby with a low platelet count and petechiae. Alternatively, they could know about it if their sibling gives birth to a baby with NAIT. This is because it is the baby who has the condition, rather than the pregnant individual.

The diagnostic process may begin with the doctor ordering a complete blood count (CBC) on the newborn test. This test can help determine whether the platelet count is within typical ranges.

HPA testing

The next step is determining the platelet antigen status of the parents and the newborn. Doctors can do this by performing serological testing on maternal, paternal, and newborn blood samples. The serologic test can determine if the birthing parent has produced antibodies against any of the platelet antigens from the other parent.

If there is a history of thrombocytopenia in a previous sibling, doctors can test the fetus before it is born. They can take a fluid sample from the amniotic sac to check the baby’s platelet type. This is called amniocentesis.


Doctors can also use ultrasound to monitor the fetus for signs of bleeding, such as intracranial hemorrhage. It can also help doctors monitor fetal growth and development.

NAIT can present with symptoms similar to other neonatal bleeding disorders. Therefore, doctors must differentiate between them to ensure prompt and appropriate treatment.

Some disorders with similar symptoms to NAIT include:

Doctors base their treatment plans on the severity of the disease, the gestational age of the fetus, and whether the doctors make a diagnosis before or after birth. The treatment goals after birth are to prevent major bleeding, particularly around the brain and gastrointestinal tract, and death.

Prenatal treatment

If doctors have diagnosed NAIT before birth, or the pregnancy is at risk, then doctors may recommend either intravenous immunoglobulin (IVIG) or intrauterine platelet infusion (IUPT).

Doctors administer IVIG to the birth parent whose pregnancies may be at risk for NAIT. Doctors give this blood product during pregnancy to prevent the formation of antibodies against fetal antigens. This treatment can begin at 16 weeks of gestation.

Alternatively, doctors may give IUPT when thrombocytopenia is already present. The infusion procedure uses local anesthesia and ultrasound guidance to infuse platelets into the fetus. However, there are risks with the procedure, including premature labor and infection. Babies can also receive transfusions after birth.

Postnatal treatment

Treatment for NAIT after birth may include:

  • IVIG or platelet transfusion, to increase platelet count
  • head ultrasound, to ensure there is no cranial hemorrhage
  • parental lab evaluations

Neonatal alloimmune thrombocytopenia (NAIT) is a rare blood disorder that affects pregnant people and their babies. It occurs when the maternal immune system attacks the fetus’s platelets, causing a low platelet count and potentially life threatening bleeding in the fetus or baby.

Symptoms of NAIT may only be apparent after birth. However, doctors can perform tests for those with at-risk pregnancies to detect the condition.

Treatment for NAIT may involve blood transfusions to raise platelet levels or infusions of immunoglobulins for the birthing parent.

It is important for pregnant people to receive proper prenatal care and to inform a doctor if they have a history of NAIT or if they have had a previous pregnancy involving the condition. With early detection and proper management, the outcome for newborns with NAIT can be positive.