The Human Fertilisation and Embryology (Mitochondrial Donation) Bill was passed by Parliament earlier this year in a bid to stop some inherited diseases.
Government ministers had argued letting a child have the DNA of two women and one man could prevent Mitochondrial Disease being inherited.
The mitochondrial donation is aimed at stopping serious inherited diseases that can be devastating to a person's life and cause early death.
Research suggests the technique could help almost 2,500 women in the UK have children.
But the Church had criticised the move at the time saying it had "serious ethical objections".
It was passed in a House of Commons free vote by 382 votes for and 127 against.
Despite the law now being passed Dr Trevor Stammers, a Christian and expert in bioethics, told Premier many scientists are still concerned.
He said it had "never been tried before" and that "many scientists are very concerned because they fear it may not work".
Mr Stammers added: "When scientists get an idea their enthusiasm sometimes exceeds their wisdom.
"We must be very cautious. I hope that it does work, but I am extremely sceptical."
Andrea Williams, chief executive of Christian Concern, said the new law was "playing God" and " undermining the very pattern for family and human dignity that God has given to us."
She added: "Even judged by the UK's generally cavalier approach to bioethics, this is a huge ethical and safety line to cross.
"Countless human embryos will be destroyed in the development of these techniques and once they are deployed, we will be embarking on a mass genetic experiment on future generations, without consent.
"There is no way of accurately predicting the consequences, but future generations will be forced to endure them.
"No wonder that, for so many in the international scientific community, this is a line that shouldn't be crossed."
Listen to Premier's Antony Bushfield speaking to Dr Trevor Stammers here: