Does anti-HPA-1a affect birthweight in fetal and neonatal alloimmune thrombocytopenia?

BACKGROUND: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) ensues from parental incompatibility for platelet alloantigens with maternal sensitization. HPA-1a/1b incompatibility is the most common cause of FNAIT in Caucasians. Placental villitis and lower birthweight in FNAIT suggest anti-HPA-1a may have effects beyond inducing thrombocytopenia. OBJECTIVES: Does FNAIT secondary to anti-HPA-1a result in smaller newborns and, the corollary, does antenatal management of FNAIT increase birthweight? STUDY DESIGN: Birthweights of 270 FNAIT-affected newborns from a randomized clinical trial and a NAITbabies.org survey (135 paired siblings) were compared with those of published controls and treated to untreated FNAIT-affected siblings. Birthweights were converted to percentiles to account for gestational age, sex, and role of birth order in birth weight. Body weights of FNAIT-affected and -unaffected pups in a mouse FNAIT model were analyzed. RESULTS: Untreated siblings in both the clinical trial and NAITbabies.org cohorts were not small, compared with normal controls. However, treated siblings in both cohorts had significantly higher birthweight percentiles compared with their previous untreated affected sibling. After accounting for gestational age, sex, and birth order, increased birthweight percentile in treated compared with the untreated siblings remained significant in both cohorts. FNAIT-affected neonatal mice had lower bodyweights than FNAIT-unaffected pups. CONCLUSIONS: Untreated FNAIT-affected newborns were not small; however, treatment of FNAIT-affected pregnancies increased newborn birthweights despite corrections to account for other factors that might have influenced the results. High dose IVIG is believed to "block" FcRn and lower maternal anti-HPA-1a levels, and thus increase birthweights by reducing levels of maternal anti-HPA-1a and reducing placental villitis.

Naitbabies - A patient organisation for families affected by foetal and neonatal alloimmune thrombocytopenia - FNAIT.

Naitbabies is a small Charitable Incorporated Organisation (CIO) (Foundation) registered in England, United Kingdom and run by families who have been diagnosed with foetal and neonatal alloimmune thrombocytopenia (FNAIT). FNAIT is a rare, life threatening bleeding disorder caused by the maternal immune response against fetal platelet antigens. Clinical research shows that approximately 1:1000 babies are affected by this disorder; of those 5-10 % will suffer internal bleeding, most particularly intracranial haemorrhage. As the only patient organisation for FNAIT, we advocate for parents worldwide; as of July 8th 2019 our Parents Support Group numbered 1250 members. We support research into FNAIT, its causes, treatment and prevention. Since 2012 we have been collaborating with scientists who have been engaged on a programme to develop a prophylactic treatment to prevent FNAIT in HPA-1a negative women. Our aim is to see routine prenatal screening for FNAIT for all pregnant women.