Why is reproductive cloning with somatic cell nuclear transfer associated with embryo loss and birth defects?

Reproductive cloning via somatic cell nuclear transfer (SCNT) is associated with high rates of embryo loss and birth defects because the process of reprogramming a differentiated adult cell nucleus to an embryonic state is complex and often incomplete.123

As Ian Wilmut observed through his pioneering work with Dolly, the biological challenges are significant: many embryos fail to survive after implantation, and those that do survive to term may die shortly after birth or suffer from developmental abnormalities. Because the donor nucleus must be "reset" by the egg's cytoplasmic factors to guide development, any failure in this reprogramming can lead to lethal errors or severe health issues in the resulting offspring.4215

Ethically, these high failure rates and the associated suffering of the animals involved are primary reasons why reproductive cloning is widely considered dangerous and impractical. Wilmut himself maintained that human cloning was both scientifically and ethically unjustifiable, emphasizing the profound risks inherent in the technology.42