Underreporting of mortality from RhD haemolytic disease in Scotland and its implications: retrospective review

Introduction

Clarke et al surveyed the decline in RhD haemolytic disease in England and Wales from 1977–92 by reviewing the statistics of the Office of Population Censuses and Surveys; during that time deaths attributable to RhD haemolytic disease had fallen from 18.4 to 1.3 per 100 000 live births.1 We surveyed RhD alloimmunisation in mothers resident in Scotland between 1987 and 91 and confirmed that fetal loss from RhD haemolytic disease was greater than that listed by the General Register Office in Scotland. Underreporting has serious implications for recognising, understanding, and preventing this potentially lethal disease.

Subjects, methods, and results

Data on deaths attributable to RhD haemolytic disease during 1987–91 were obtained from: death certificates; details of pregnancies in Scottish residents who had antibody to RhD antigen and were managed at the Queen Mother's Hospital; and a retrospective study identifying women in whom RhD antibodies were detected for the first time during 1987–91 (1). The definition of mortality from RhD haemolytic disease included all abortions after fetal death, stillbirths, and neonatal deaths attributed to RhD incompatibility or its treatment and deaths after 28 days of life in which RhD haemolytic disease or its treatment was the primary cause.2

Only four deaths were listed by the General Register Office in Scotland; all were neonatal deaths occurring in women immunised against RhD before 1987. Four deaths occurred in the cohort but none were listed through the General Register Office in Scotland. Twelve other pregnancies managed at the Queen Mother's Hospital during this time (mothers alloimmunised before 1987) resulted in deaths related to RhD haemolytic disease. Ten of the pregnancies ended with abortions after fetal death, and two resulted in liveborn infants treated in utero by repeated blood transfusions. These two infants were delivered electively more than two months preterm but died from complications on the first and 95th days of life.

Thirteen of the 20 deaths resulted from alloimmunisation against RhD antigen during a first pregnancy. In four cases maternal RhD antibodies were first detected within two days of delivery, and in the remaining nine during gestation. There was also good documentation of antepartum immunisation in relation to at least two of the deaths from second pregnancies.

Comment

A review of the case notes of deaths recorded as Rh haemolytic disease in England and Wales showed that disease was often caused by antibodies other than RhD antibody or was wrongly coded. Our data show that five times as many deaths from RhD haemolytic disease were uncertified as were certified through the General Register Office in Scotland. The major cause of underreporting deaths was that certification data exclude abortions. Extrapolation of all the deaths from RhD haemolytic disease identified in Scotland to the population of the United Kingdom would suggest about 50 deaths per year (six per 100 000 live births).

Antepartum prophylaxis against RhD antigen is used widely outside the United Kingdom, and in North America alloimmunisation has been reduced to less than 0.3% of women at risk.3 The standard British dose of 500 international units of anti-D immunoglobulin administered at 28 and 34 weeks' gestation reduced alloimmunisation from 0.95% in historical controls to 0.32%,4 and we have recently shown that this approach could generate net savings to the NHS in Scotland by avoiding the costs of intervention in alloimmunised women and their babies.5

Our data support the introduction of routine antepartum prophylaxis as 65% (13/20) of deaths from RhD haemolytic disease were the eventual results of antepartum sensitisation in the mothers' first pregnancies and 65% of women seen at the Queen Mother's Hospital were alloimmunised during and not after a pregnancy.2