The SDLP will oppose changing the law on abortion which would allow a termination if a woman is raped or carrying a foetus with a lethal abnormality.
Speaking to the BBC, party leader Dr Alasdair McDonnell said:
"The SDLP is unequivocally opposed to abortion, even in those particular circumstances because basically, the predictions in those circumstances are never accurate," he said.
"Nobody can predict that a foetus is not viable, and that's the problem, and as a GP, I'm fully aware.
"I have seen situations where termination or an abortion was recommended to somebody because a foetus that had this, that or the other thing, and that foetus grew up to be a perfectly normal child."
His comments come as Justice Minister David Ford continues a public consultation on amending the criminal law on abortion in Northern Ireland.
Abortion law in Northern Ireland differs from the rest of the UK.
Unlike other parts of the UK, terminations are currently only legal in the region to protect the woman's life or where there is a risk of permanent and serious damage to her mental or physical health.