Aims: Fetal blood cells enter the maternal circulation in up to 95% of pregnancies, but usually in minute volumes. Haemodynamically significant fetomaternal haemorrhage (FMH) is a much rarer event reported in approximately 1 in 2800 pregnancies. Most of the literature on this phenomenon emphasises the clinical aspects, and there is no comprehensive description of the autopsy findings. We present a series of five fatal FMH. The aim of this series is to highlight some of the autopsy findings that may prompt consideration of a diagnosis of FMH and lead to appropriate confirmatory testing and counselling of the affected couple.
Methods: The five cases were referred to the Children's Hospital at Westmead for full autopsy. A Kleihauer-Betke test was performed on the mother's blood within one week of delivery in each case.
Results: The infants ranged in age from 27 to 40 weeks gestation (mean 36.6 weeks) with a mean birth weight of 2793 g. The estimated volumes of fetal blood lost ranged from 443 to 104 mL (mean loss 243 mL). The estimated percentage of fetal blood volume loss was an average of 107% (i.e., greater than the entire blood volume of the fetus). No other causes of hydrops were identified. Pallor was often noted, and in most cases the autopsies were markedly bloodless with large vessels collapsed. Where the brain:liver ratio could be applied, two fetuses showed a mild increase in ratio, while one infant showed moderate growth restriction with a ratio of 6.2:1 (normal ratio 2.8:1 on non-macerated fetuses over 28 weeks gestation). Placental abnormalities included thrombosis of the umbilical vein and intervillous 'haematomas' in two cases. The most striking microscopic feature was the presence of intravascular nucleated RBC within virtually all organs. Placental intervillous (i.e., within the maternal vascular compartment) nucleated red blood cells were also seen in all cases.
Conclusions: The autopsy findings of FMH can be subtle and easily overlooked unless a high index of suspicion is maintained. The most reliable autopsy features are pallor, subcutaneous oedema or serous effusions, and intravascular nucleated red blood cells (RBC) in organs or more specifically in the placental intervillous space. In all cases of unexplained fetal death a Kleihauer-Betke test should be performed.