When Dr. David Keefe and colleagues* compared the outcomes of implanting 2,452 'fresh' embryos and 392 frozen and thawed out embryos into the uterus, they found that using frozen embryos resulted in 17 times as many (potentially fatal) ectopic pregnancies.** Other research found genetic damage in frozen embryos. The UK's Human Fertilisation and Embryology Authority expressed serious concern.

The findings were presented to the 2003 Conference of the American Society for Reproductive Medicine.

* ..at Brown University in Providence, Rhode Island (US)
** where the embryo develops in a Fallopian tube rather than in ....the womb