In 1941 Levine and his colleagues postulated that the way in which Rh sensitization occurred in Rh negative mothers was by transplacental passage of Rh-positive foetal erythrocytes into the maternal circulation. At that time there were no available tech' niques for proving this hypothesis, and it was not known when the foetal cells entered the maternal circulation, nor how much foetal blood was...

A second trimester fetal demise followed influenza-like illness in early pregnancy. Influenza A virus (H1N1) was identified in maternal and fetal tissue, confirming transplacental passage. These findings suggested a causal relationship between early exposure and fetal demise. Management of future influenza outbreaks should include evaluation of products of conception associated with fetal loss.