ABSTRACT
The timing and strength of embryonic signals probably allow the mother to evaluate the fitness of a conceptus and to terminate a pregnancy before investment is too high. Embryos that possess chromosomal abnormalities, that are developmentally stunted, or are suffering setbacks as the result of detrimental environmental and nutritional conditions in the uterus, are likely to be delayed in their development and to signal less than robustly to the mother.[1,2] Accordingly, deficient MRP signaling probably underpins much of the early embryonic loss that occurs in the first three weeks of pregnancy.
