Anti-HPA-1a antibodies in pregnancy and fetal growth – an analysis of registry data from a previous prospective screening study

Abstract

Background: A previous retrospective study found a strong association between increasing levels of maternal anti-HPA-1a antibodies and reduced birth weight in boys, and demonstrated increased frequency of small for gestational age (SGA) newborns among mothers with high levels of anti-HPA-1a antibodies during pregnancy. We aimed to use prospective data from a previous HPA-1a screening study to assess if the maternal anti-HPA-1a antibody level affects fetal growth and placental function using various ultrasound parameters and also to study the birth weight and frequency of SGA among HPA-1a immunized women. Methods: We studied various parameters of fetal growth and placenta function in HPA-1bb alloimmunized pregnant women identified through a previous large Norwegian prospective screening study. Pregnancies from non-immunized HPA-1bb women were not included. Repetitive fetal ultrasound data (parameters of fetal growth and placental function) were collected from the mothers’ medical journals. We also assessed birth weight and frequency of SGA among boys and girls. Results: 135 women with detectable anti-HPA-1a antibodies were identified and included in the study. These 135 women completed a total of 142 pregnancies. 31.1% of the women included were nulliparous. The mean birth weight in the study population was 2995 grams and the frequency of SGA was 11.4%. Preliminary results demonstrates a non-significantly higher frequency of SGA among boys (20%) than girls (5.0%) (chi-square test, p=0.092). Conclusion: A higher frequency of boys among alloimmunized women was demonstrated (not significant). The frequency of SGA was also higher among boys than girls (not significant). Reduced birth weight and SGA should be considered a possible complication of maternal anti-HPA-1a antibodies occurring during pregnancy.