Amniocentesis is an accurate but invasive prenatal procedure to diagnose genetic, chromosomal or immune-related disorders in the fetus.
Initially used as a standard tool in the diagnosis of fetal and neonatal alloimmune thrombocytopenia (FNAITFetal and neonatal alloimmune thrombocytopenia A rare condition in which a mother’s immune system attacks fetal platelets, leading to dangerously low platelet levels before and/or after birth.) during pregnancy, the use of amniocentesis has reduced significantly in recent years, replaced by non-invasive medical options of less risk to the fetus.
What is FNAIT?
Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare but serious condition that affects 0.1% of pregnancies in which a pregnant mother’s immune system produces antibodies against the platelets of her fetus. This occurs when a fetus inherits platelet antigens from the father that are not compatible with the mother, typically involving a protein called human platelet antigen (HPA). The mother’s immune system recognizes the fetal platelets as foreign, attacking and destroying them, leading to low platelet levels (thrombocytopenia) in the fetus or newborn.
What is amniocentesis?
Amniocentesis is an invasive medical procedure performed on the fetus during pregnancy to diagnose a variety of conditions, including genetic disorders, congenital abnormalities and infections. It can also be performed to reduce the volume of amniotic fluid in rare cases where there is an excess amount.
A long needle is inserted into the amniotic sac with the guidance of ultrasound imaging and extracts amniotic fluid rich in fetal cells, transudates, fetal urine and lung secretions. The timing of the test is important, with the safest window considered between 15 and 20 weeks’ gestation.
How is amniocentesis used in FNAIT?
Amniocentesis was traditionally used to diagnose FNAIT by performing fetal genotypingGenotyping A laboratory test that identifies which platelet antigens a person carries. Often used to confirm HPA incompatibility and assess recurrence risk. on the discarded fetal cells found in amniotic fluid. However, in recent years, the focus has shifted to safer, less invasive alternatives such as cell-free fetal DNA testing (cffDNA). In pregnancies suspected of FNAIT, amniocentesis is therefore rarely used.
Risks of amniocentesis in FNAIT
As an invasive procedure, amniocentesis can lead to complications that cause discomfort for the pregnant mother, fetal distress and potentially fetal death. The most common complications include leaking amniotic fluid, bleeding, severe cramps, infection, preterm labor and miscarriage.
In FNAIT, amniocentesis increases the risk of the intervention, upping the risk of fetal loss and complications by 11%.
Alternatives to amniocentesis
Fetal genotyping by cffDNA, testing for maternal antibodies and maternal and paternal HPAHuman platelet antigen Proteins found on the surface of platelets. Incompatibility between maternal and fetal human platelet antigens can trigger FNAIT. genotyping to assess the risk of FNAIT are all used in diagnosing FNAIT in pregnancy.
If FNAIT is suspected, the current standard of care is to administer IVIGIntravenous immunoglobulin A treatment given to pregnant women with a history of FNAIT or known alloantibodies. IVIG reduces the immune reaction against fetal platelets. with or without steroids as soon as possible to delay the onset of severe thrombocytopeniaSevere thrombocytopenia A dangerously low platelet count, typically below 50,000 platelets per microliter and sometimes far lower in FNAIT.. Following delivery, the newborn will receive platelet transfusions to boost blood platelet levels and, in most cases, symptoms will be resolved.
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