As France braces this weekend for giant protests against gay marriage and adoption, neighbouring Belgium has become a haven for French lesbians, who flock there in their thousands to conceive babies they are denied at home.

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Some 2,000 babies conceived in Belgium through artificial insemination by donor are thought to be born each year to French lesbian couples, who are not eligible to undergo the procedure in France.

"We have seen a sharp increase in demand over the past three years. The word is getting around in France, our patients are passing the message along," said Professor Michel Dubois at the University Hospital of Liege, in the southeast of the country.

The children thus conceived even have a nickname – "Thalys babies" – after the high-speed train service between Brussels and Paris on which their mothers shuttle back and forth – sometimes for years – in their quest to become parents.

Plans by France's Socialist government to extend marriage and adoption rights to gay couples have proven deeply divisive, igniting fierce protests from opponents including Catholic and Muslim leaders, with a new mass rally planned in Paris for Sunday.

Reflecting the heated debate, ruling party lawmakers agreed Wednesday to drop an amendment expanding access to artificial insemination services from the same-sex marriage legislation.

By contrast Belgium, which has allowed same-sex civil marriages since 2003 and prides itself on its gay rights record,  artificial insemination is available to all "regardless of civil status or sexual orientation" under a 2007 law. 

The country has become a mecca of sort for lesbian couples, with 18 centres nationwide offering the procedure and catering to an overwhelming majority of French women. "French mothers accounted for 80 percent of the 833 artificial insemination cases we handled last year," said Dubois.

At the largest hospital in Brussels, the Erasmus University Hospital, demand is such that it allows only two days a year for patients to phone and arrange consultations.

"In just an hour and a half, all the appointments available for the next six months are taken. That causes a lot of frustration but there is nothing we can do about it," said Anne Delbaere of the hospital's fertility clinic.

‘Dozens of trips back and forth'

Those French lesbians who manage to get an appointment then embark on a long, difficult and sometimes painful journey but when things go right, it is worth the agony, they say.

"It was torture but we happily forgot all about that when Achilles was born," said Katell Thepault, a midwife from near Nantes in western France. "It took more than three years, with dozens of trips back and forth to Brussels for what turned out to be nine artificial inseminations and two in-vitro fertilisations," Thepault, 35, said.

Everything, her personal life with her partner and her working career, all turned around these trips. "It was impossible to know in advance when we would have to go to Brussels. We were given only 48 hours’ notice. We would drive at night, for eight hours," she said.

And the cost? "It was really expensive. We nearly gave up when the artificial insemination did not work and we had to try the in-vitro procedure," at a cost of about 3,000 euros, Thepault said. For a simple insemination the cost ranges from 350 to 500 euros.

For Marie, also mother to a 'Thalys Baby', "it was galling to have to spend so much money when (French) heterosexual couples get the cost reimbursed. It would be much less hypocritical if women could get this service in France because the politicians know very well that we go to Belgium or Spain for it," she said.

Even in Belgium, there are some limits to the principle of open access for lesbians. Some fertility centres have traditional links with the Catholic church – a powerful opponent of the French government's plans – and so prefer not to take on lesbian couples.

Other medical centres limit the help offered to French and other foreign mothers so as to ensure there are enough services available to local women. Brussels' Erasmus University Hospital accordingly treats only perhaps a 100 foreign women a year.

"It is a decision we had to take because of a shortage of sperm donors and a sharp increase in demand for help in cases not caused by infertility problems," said Delbaere.

Delbaere says she cannot understand the French reluctance to grant lesbians access to medically-assisted procreation, which is offered only to heterosexual couples facing fertility problems.

"It seems to me that they just do not want to accept a reality which has been there for a long time now. These children, these families are there now, whether one likes it or not. Why continue to deny it?"