Earlier reports have indicated that the transfers of bovine and ovine embryos produced by in vitro procedures (IVP) or by nuclear transfer (NT) have resulted in the birth of heavy offspring. The present paper presents summary information from 30 data sets obtained worldwide (WW) on IVP and NT in different cattle breeds, plus the preliminary results from a highly controlled field study (FS) undertaken by Holland Genetics (HG) on Holstein-Friesian IVP calves. Data of artificial insemination (AI) and embryo transfer (ET) served as controls. The results from the WW and FS trials were very similar. After adjusting for such effects as season, parity of cow/recipient and sex of calf, foetal losses between pregnancy diagnosis and term were higher for IVP and NT embryos. In addition, both gestation length and birth weight were increased relative to AI and ET calves, and there were also higher incidences of Dystocia, perinatal loss and anomalies. The increased incidence of these problems has important implications for animal health and welfare, as well as affecting the commercial acceptance of these techniques. Research should focus on each step in IVP and NT procedures and on the synchrony between embryo and uterus at transfer, to understand and overcome these problems.