MPs proposed the amendment to a 2004 bill, which makes it compulsory for couples to have premarital check-ups so they are aware of the chances of their children being born with a disease.
Parliament wanted a judge to determine whether or not couples could wed if they had conditions such as sickle cell anaemia, thalassaemia, HIV, hepatitis and syphilis.
The amendment had already been approved by the Cabinet, but it was voted down by the Shura Council yesterday on the grounds that it should be up to each couple to decide whether or not they want to take the risk of passing on a condition to their children.
"It is up to the couple if they want to continue with their marriage knowing the consequences," said Shura Council services committee chairman Abdulrahman Abdulsalam.
"They have to sign a document accepting responsibility before a certificate is issued so they can get married.
"Going to court for permission to get married is unnecessary because judges are not concerned with medical affairs that are top secret and have no right to stop anyone getting married.
"It would also mean that many people would be waiting for their turn in court.
"We urge the Health Ministry to focus on studies that could help cure those diseases in future."
Committee secretary Abduljalil Al Oainiti said there would be massive waiting lists if people with hereditary diseases or sickle cell carriers gene had to go to court before getting married.
"Most of the Shi'ite community - we are speaking about thousands of carriers and sufferers of hereditary illnesses - will be forced to wait in court before getting to a judge, who will just inform them about the consequences and then be forced to give permission anyway," he said.
Council public utilities and environment affairs committee vice-chairman Faoud Al Haji said barring people from getting married in such circumstances was inhumane.
"Sick people have every right to get married as anyone else," he said.
"Illness is not a barrier. God knows, tomorrow's parliament could come up with an amendment that bars people with a certain IQ from getting married."
Health Ministry acting woman and child care head Dr Hala Al Asoomi explained couples were properly educated on the risks.
She said some agree to cancel their weddings if it is likely that their children could suffer from conditions such as sickle cell anaemia, as a result of both parents being carriers.
However, she added there were others who could not be deterred.
The ministry's acting hereditary diseases head Dr Amani Al Hejari added that couples are briefed on the dangers if they are carriers of such genes and are given a period to rethink.
"Most are determined and have come with a fixed mind, so we can't influence them on either proceeding or having the marriage cancelled," she said.
"But we urge legislators to stop clergymen issuing fatwas (religious rulings) allowing mothers to abort if they have hereditary diseases." firstname.lastname@example.org