The Center for Disease Control recommended that all expectant mothers receive the H1N1 vaccine.  Data from a UK study released by The Lancet suggests that the spontaneous abortion rate within 1 day of vaccination with the H1N1 vaccine will be 397 per 1 million.  That means of the approximately 4.7 million births in the US (data projected from the National Vital Statsitics System from 2007) this year,  1707 expectant mothers will lose their babies as a direct result of the vaccine.

Steven Black, Juhani Eskola,  Claire-Anne Siegrist  ,Neal Halsey , Noni MacDonald , Barbara Law,  Elizabeth Miller, Nick Andrews, Julia Stowe, Daniel Salmon, Kirsten Vannice , Hector S Izurieta , Aysha Akhtar , Mike Gold , Gabriel Oselka , Patrick Zuber,  Dina Pfeifer, Claudia Vellozzi (2009).  "Importance of background rates of disease in assessment of vaccine safety during mass immunisation with pandemic H1N1 influenza vaccines."  The Lancet 374 (9707) Pages 2115 - 2122.