Three PN MPs voted against a new IVF law which otherwise enjoyed cross-party support on Wednesday.
The law passed with 66 votes in favour and three against.
It is understood that opposition MPs Adrian Delia, Alex Borg, and Ivan Bartolo voted against the reform, which had made conservative members of the Opposition uncomfortable. MPs voted electronically.
The new IVF law will allow genetic testing prior to implantation to enable doctors to look out for certain conditions such as Huntingtons' Disease.
It had been a headline pledge of the Labour Party in the March general election.
Prime Minister Robert Abela had pledged to deliver the reform within the first 100 days of his administration which drew to a close on Wednesday.
An Opposition amendment for what is known as polar body testing was taken on board.
This type of test happens on oocytes which have not been fertilised.
When the law was put for a vote on Wednesday a division was called and Opposition MP Adrian Delia asked for MPs to vote individually.
He declared he is in favour of life - from beginning to end and "this is why I will be voting against the motion”.
Delia had hinted that he would be voting against the reform in a social media post on Sunday.
On Wednesday, PN health spokesman Stephen Spiteri said he was speaking in the name of the rest of the group who would be voting in favour of the motion.
As a healthcare professional, he said, he trusted other healthcare professionals to take the right decisions.
PN MPs Carm Mifsud Bonnici, Chris Said, and Jerome Caruana Cilia were not present for the vote.
In a tweet shortly after the vote, Health Minister Chris Fearne thanked all MPs who voted in favour of the reform.
On Sunday, Grech said that, after the government took on a number of amendments put forward by the PN, the opposition decided to vote in favour of the law.
But a number of PN MPs who spoke to Times of Malta earlier this week said they felt the law still goes against their ethical principles.
Faced by reporters on their way out of parliament none of the three MPs gave any comments.
Delia said he had nothing to add to his statement in the House. Bartolo also declined to comment while Borg refused to even interact with the media, requesting an aide to tell journalists not to approach him.