Does maternal platelet-associated or platelet-bindable IgG correlate with levels in umbilical cord blood or colostrum during normal pregnancy?
Existing data regarding the ability to predict neonatal thrombocytopenia during maternal immune thrombocytopenia are confusing. We studied normal pregnancies (n = 20) to define normal values and the correlation between maternal and umbilical cord platelet counts, platelet-associated immunoglobulin G (IgG), and platelet-bindable IgG. The postpartum serum platelet-bindable IgG level was measured to evaluate peripartum changes and the correlation with colostrum platelet-bindable IgG (n = 6). The mean maternal platelet count was 181,500 cells/cm3 mm and the mean umbilical cord platelet count was 293,500 cells/mm3. The median maternal platelet-associated IgG was 803 molecules per platelet, umbilical cord platelet-associated IgG was 791 molecules per platelet, maternal platelet-bindable IgG was 92 molecules per platelet, and umbilical cord platelet-bindable IgG was 256 molecules per platelet. The postpartum median maternal platelet-bindable IgG was 333 molecules per platelet and for colostrum it was 297 molecules per platelet. No clinically useful correlations for predicting the neonatal platelet count during normal pregnancy were found. Normal pregnancies may have high levels of maternal- or umbilical cord platelet-associated IgG, perhaps due to nonspecific binding.