Large study of maternal alloimmunization yields a surprise

September 21, 2016

Relative risk of stillbirth and preterm birth associated with less well-known antibodies was of similar magnitude to that found for anti-D.

Maternal anti-Lea antibodies, red cell antibodies not usually thought to be a risk factor for adverse pregnancy outcomes, were found to increase the risk of stillbirth in a large study performed in Sweden and published in 2014. Rh and K-red blood cell antibodies also were found to increase the risk of both preterm birth and stillbirth. The study was published in the International Journal of Epidemiology.

In a study sample consisting of 1,022,569 singleton pregnancies from 668,952 mothers in Sweden during 1987–2002, 1.3% were alloimmunized. The researchers ran adjusted logistic regression models and, compared with having no antibodies, alloimmunization with anti-D, anti-E, anti-C and anti-c was associated with increased risk of both stillbirth and preterm birth. In addition, anti-Kell was associated with increased risk of preterm birth and anti-Lea with increased risk of stillbirth. Compared with firstborns, children of subsequent births had a higher risk of preterm birth.

The researchers claimed that this study was the largest as of 2014 to look at both Rhesus and non-Rhesus maternal alloimmunization and called for further investigation of the consequences of non-anti-D alloimmunization. They noted, “In our study sample, anti-D antibody occurred at a frequency comparable to other antibodies (e.g. anti-Lea, anti-E) that are not as well studied and which do not have prophylactic treatments. However, the relative risk of stillbirth and preterm birth associated with these less well-known antibodies was of similar magnitude to that found for anti-D.”