• Blastocyst development;
  • serum factors;
  • recurrent spontaneous abortion

Some cases of unexplained recurrent pregnancy loss may be due to embryotoxic factors present in the mother's serum. In vitro assays have been devised to study the effect of these factors on pre-implantation, peri-implantation, and somite stage rodent embryos. Embryotoxic activity has been found in a high percentage of recurrent aborters but is also present in women with endometriosis and unexplained infertility, suggesting that there may be a range of factors acting at different stages of development. Embryotoxic activity may be predictive of pregnancy outcome and has been shown to be decreased after hormone and immunotherapy. However, its true value can only be assessed when the nature of the toxic factors is understood. Preliminary characterisation studies suggest that toxic activity may due to both immunological (antibodies or cytokines) and nutritional factors.