British couples are travelling to America to enable them to select the sex of their children.
The process, known as PGD (pre-implantation genetic diagnosis), involves screening embryos created through IVF before implanting one of the desired sex.
The UK bans the use of PGD to test for sex, although it is permitted to detect genetic diseases.
However, half the embryos currently awaiting the test in a New York laboratory are reportedly from British couples.
Many countries restrict the use of PGD because of concerns it could be exploited in cultures with a preference for male heirs.
There is also opposition to the destruction of the unwanted embryos left at the end of the process.
Dr Jeffrey Steinberg, who opened the Manhattan clinic in January, provoked anger earlier this year when he said it could allow parents to produce “designer babies” – choosing eye, hair, skin colour and sex.
A spokesman from the UK’s Human Fertilisation and Embryology Authority pointed to the failings of the US system.
The spokesman said: “In the US there is no official regulator to monitor clinics and no legal obligation to offer the counselling that is an important part of treatment.”
Earlier this month, a Chinese study conducted on mice revealed memory decline in adulthood, sparking fears that PGD testing could increase the risk of offspring developing neurodegenerative disorders.
The study, published in the journal Molecular and Cellular Proteomics, found that successful births from tested mouse embryos were significantly lower than from those which had not been tested.
Once fully grown, the mice tested as embryos had, on average, higher body weight and poorer memory in maze tests.
Study co-author Yang Yu said: “This study indicated an increased relative risk of neurodegenerative disorders in the offspring generated.
“More studies should be performed to address the possible adverse effects.”