Labour is calling for a ban on parents-to-be being told the sex of their baby after early blood tests, amid fears it may lead to abortions of girls.
The Non-Invasive Prenatal Test (NIPT) is used by the NHS to test for genetic conditions, but people can pay for it privately to discover a baby's sex.
Labour MP Naz Shah said it was morally wrong for people to use the test to abort pregnancies based on the outcome.
The Department of Health said it would continue to review the evidence.
An investigation by the Victoria Derbyshire programme has found thousands of British women discussing using NIPT to determine sex on an online forum.
Ms Shah, who is shadow women and equalities minister, said cultural practices in some communities like the South Asian community, have a preference for boys.
She said this put great strain on women "forcing them to adopt methods such as NIPT to live up to expectations of family members".
NIPT involves taking a sample from the woman to look for DNA from the baby circulating in her blood, to gauge the risk of possible genetic conditions such as Down's syndrome. It can also be used to determine sex, information which NHS doctors will not be sharing with parents when the test is rolled out across England next month.
Private clinics offer the same test for around £150-£200 and do share this information. Some require only that a drop of blood be sent in the post with results sent back in a few days.
Ms Shah said: "NIPT screenings should be used for their intended purpose, to screen for serious conditions and Down's syndrome.
"The government needs to look into this exploitative practice and enforce appropriate restrictions."
'I had a panic attack when they said it was a girl'
Zara, not her real name, is Sikh and lives in Greater London.
"I had straightaway made that decision that I didn't want to have this baby.
"We were a family of five girls and every time my Mum had another daughter everyone would come to the house as if they were coming to mourn.
"For them it's like a burden. My fear was I didn't want to go through what my mother went through."
Zara discovered the sex of her baby five months into her pregnancy and opted to have a surgical abortion.
She now regrets the decision. "You see friends and family that have daughters and they have such a lovely relationship. I'm someone's daughter and someone's sister," she said.
Zara says she believes abortion on the grounds of sex is a "very common" practice.
Rani Bilkhu from the Jeena International organisation says many women say they have suffered violence or been coerced into abortions because they were pregnant with a second or third girl.
It wants sex-selective abortion to be viewed as a form of honour-based violence.
"No wonder they're resorting to sex-selection abortion because they've got no choice," she says. "They don't want to be homeless, they don't want their marriage to fail - all because they couldn't give birth to a boy."
'Only if it's a boy'
The online forums where British women discussed using NIPT include thousands of posts where women express their anxiety about having a girl.
One said: "I need a son to heal me... my only bet is NIPT followed by continuation, only if it's a boy."
The programme also found one area, Slough, where women's clinics offering these tests were being promoted on roadside adverts.
"This poster is really telling the community, 'Come here, come to us and we'll let you know whether you're having a boy or a girl,'" says Ms Bilkhu.
Labour MP for Slough, Tan Dhesi, said marketing tests offering sex determination should be stamped out.
"Communities in South Asia have made huge strides in tackling this social evil," he said. "That's been primarily through legislation, banning gender determination clinics. In the UK I think we need to be doing likewise, with regards to the private sector as well."
Choosing an abortion due to sex is illegal in the UK, apart from some rare exemptions, but it is difficult to detect as women often cite other reasons for having the procedure.
In 2015, the government acknowledged it did not know how widespread testing for sex was. It said if NIPT became more popular, it would need to analyse the impact it was having on the gender ratio in ethnic minority communities.
Ms Bilkhu said it was extremely hard to measure.
"Not only do the government not understand there's an issue around sex-selection abortion, but also charities and statutory sectors aren't asking the questions," she said.
The Nuffield Council, which advises on ethical issues, recently held a consultation on NIPT testing. It believes the ability to determine sex reinforces pressure on women to have boys.
"The desire for sex-selection is a major driver of private-sector testing," said Tom Shakespeare from the council. "I don't think the government want to regulate, they just don't like it in any sector.
"But countries like China and India have recognised the problem of sex-selective abortion and so it's very difficult to get this information - in India it is illegal. So if we allow it, people will come here as tourists."
A Department of Health and Social Care spokesman said: "The pre-natal test is never meant to be used for determining the sex of a child. We will continue to review the evidence."
Watch the BBC's Victoria Derbyshire programme on weekdays between 09:00 and 11:00 on BBC Two and the BBC News channel in the UK.