Anti-abortion group Both Lives Matter, which is a coalition of groups including CARE and the Evangelical Alliance, faced a challenge when 14 complaints said the claim could not be backed up - despite a robust report.
However, Dawn McAvoy from the pro-life group told Premier that recent research did back up their claims.
Speaking during News Hour she said: "We did face criticism. We knew that pro-abortion groups would not be happy about that claim because the commonly used language that law doesn't stop abortions.
"And we have now shown that law does stop abortions."
Northern Ireland is the only part of the UK where terminations remained banned after the 1967 Abortion Act was introduced in Great Britain.
Explaining the decision, an ASA statement read: "On balance, we concluded that the evidence indicated that there was a reasonable probability that around 100,000 people were alive in Northern Ireland today who would have otherwise been aborted had it been legal to do so.
"Because we considered that readers would understand the figure to represent an estimate, we concluded that the claim was unlikely to materially mislead readers."
Both Lives Matter said the calculation which was based on a comparison with Scotland's abortion ratio, represented a credible and conservative estimate.
McAvoy added: "This independent verification is a real endorsement of our campaign.
"We wanted people to realise that this had changed the lives of everyone."
Listen to Dawn McAvoy speaking with Premier's Tola Mbakwe:
