The unnamed teacher and her husband are said to be ecstatic about the pregnancy, which was achieved with fertility treatment after they suffered two miscarriages. They are expecting six boys and six girls and the woman is thought to be as much as nine months' pregnant.
But fertility experts have condemned the news, alleging the doctors who treated the couple are "irresponsible" and risking the health and lives of the mother and her babies.
It is not known what fertility treatment the woman had, but her husband was quoted by local papers as saying they had been expecting twins.
She is said to now be looking forward to hugging her babies and, according to her husband, has been told she can give birth naturally although experts say this is impossible.
The man, who was named only as Marwan and is a teacher of Arabic at a high school in their home town of Gafsa, southwest of the capital Tunis, told a local journalist the news was an "amazing and wonderful miracle".
"In the beginning, we thought that my wife would give birth to twins, but more foetuses were discovered," he was quoted as saying.
"Our joy increased with the growing number."
But Simon Fisher, a fertility expert from the University of Oxford, said the news of the duodecaplets was "horrendous" and said the doctors involved were "irresponsible" to allow it.
He said the pregnancy could have been achieved either because the couple ignored the advice of doctors and had intercourse during their treatment, conceiving naturally as well as through IVF, or religious reasons required all the embryos to have been used rather than some being destroyed.
"Whatever the reasons behind this, the chances of there being a happy ending are pretty remote," he said.
"The chances of all of them surviving are extremely remote and the chance of some of them surviving without any problems is unlikely - they are likely to have significant problems.
"Her chances of surviving depend on how well she is monitored. It will be a tremendous strain on her even if she is young and fit. IVF is practised responsibly all over the world and no one should ever get into this situation."
Dr Mark Hamilton, of the British Fertility Society, said the woman probably had ovulation induction treatment, which sees the woman have either tablets or injections to cause her to release an egg to be fertilised.
"Twelve babies seems extraordinary," said Dr Hamilton. "The woman could have been receiving ovulation induction treatment, which stimulates egg production. You don't have the same control as with IVF."
No one is thought to have ever given birth to 12 babies before.
In January, American Nadya Suleman gave birth to the world's longest surviving octuplets, conceived through IVF.
In May, a 29-year-old British woman, Nuala Conway, gave birth to the country's first sextuplets for a quarter of a century. One girl of the four girls and two boys, died last month.
In 1996, another Briton, Mandy Allwood, became pregnant with octuplets after taking fertility drugs.
She was offered the chance to terminate some of the foetuses to give the others a chance of survival but declined. The octuplets - six boys and two girls - were born over a period of three days and all died within an hour.
