Researchers developed a novel, noninvasive fetal human platelet antigens (HPA) genotyping tool, that may be a safe and reliable method for the early identification of pregnancies at high risk for fetal and neonatal alloimmune thrombocytopenia (FNAIT), according to a study published in the British Journal of Haematology.

The investigators used cell-free DNA from plasma samples from 47 pregnant women with suspected or history of FNAIT to conduct droplet digital polymerase chain reaction (ddPCR) within 4 HPA systems (HPA-1, -3, -5 and-15). Negative control samples were from a nonpregnant woman and a healthy pregnant woman with no HPA incompatibility with her partner.

Following HPA genotyping, 26% of pregnant women were compatible with their fetus and 74% were incompatible; 47%, 17%, and 10% of women were incompatible in 1, 2, or 3 combined HPA systems, respectively.

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HPA-1 incompatibility, which has previously been estimated to account for 80% of FNAIT events, was identified in 51% of the cases. HPA-3, HPA-5, and HPA-15 incompatibility were identified in 37%, 34%, and 29% of cases, respectively. Exclusive incompatibility in HPA-3, HPA-5, or HPA-15, was identified in 2, 7, and 4 women, respectively.

Intracranial hemorrhage occurred in 1 case with HPA-15 incompatibility. The authors emphasized that these findings confirm the need for noninvasive prenatal genotyping in systems other than the HPA-1 system.

After amniocentesis or delivery, the investigators confirmed the fetal HPA genotypes for all FNAIT cases.

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“Fetal HPA genotyping on maternal plasma based on ddPCR is a fast, safe and reliable [noninvasive method],” wrote the authors. “This technique will be useful for the early identification of pregnancies at high risk of FNAIT requiring antenatal management to minimize the risk of fetal/neonatal haemorrhage.”

Reference Ouzegdouh Mammasse Y, Chenet C, Drubay D, et al. A new efficient tool for non-invasive diagnosis of fetomaternal platelet antigen incompatibility [published online April 7, 2020]. Br J Haematol. doi: 10.1111/bjh.16593