The effect of the Rh negative disease on perinatal mortality Evidence from Skellefte̊a 1840-1900

Background The Rh-negative gene is a well known cause of perinatal mortality especially before there were any effective treatment. The Rh disease, that is caused by a Rh positive foetus carried by a Rh negative mother, leads to typical patterns of perinatal mortality with an increase of mortality with parity and mortality clustered in families. This effect has been largely neglected in earlier papers trying to explain mortality patterns in historic data. Objectives This paper highlights the role of this gene in causing these patterns and tries to quantify the effect in a society with a large group of Rh-negative persons and no access to treatment. Methods The risks of the Rh disease is approximately known from the medical literature. Knowing family sizes and the approximate share of Rh negative genes the ”theoretical” patterns of perinatal mortality can be calculated and simulated. Comparing these figures with observed patterns of perinatal deaths the relative importance of Rh factor can be estimated. We have used data from 1840-1900 in the Swedish parish of Skellefte̊a where we have data on all births and their outcomes as well as good estimates of the Rh negative gene frequency. Results The results show that the Rh gene is likely to have had an important role in perinatal mortality and the patterns with more dead at high parities and clustering explaining a relatively large part of these phenomenon in high Rh negative gene societies. Conclusions The paper shows that the Rh-disease is an important factor in understanding mortality patterns. Its great effect on the patterns makes it necessary to take it into account when analysing other factors that can affect perinatal mortality patterns.