Ann Keen voted to maintain the upper time limit for abortion at 24 weeks on Tuesday night.
In one of the most highly charged Commons debates for years, the Brentford & Isleworth MP rejected several attempts to cut the deadline by up to half.
MPs were allowed a free vote on the emotive issue and the closest bid, for a 22-week cut-off, was defeated by just 71 votes.
It was the first major challenge to Britain's abortion laws since 1990, when the time limit was reduced from 28 weeks.
Gordon Brown voted against cutting the limit to 22 weeks but Tory leader David Cameron backed the change. Alan Keen, MP for Feltham & Heston, did not vote.
The debate centred around whether medical advances had improved the survival rates of babies born before 24 weeks.
Research published earlier this month by the British Medical Journal suggested they had made little difference.