A phenomenon of “missing girls” could be afflicting Australia, as a study of more than a million births suggests some parents could aborting unborn female babies or undergoing embryo selection overseas  to have a son.

If nature was left to take its course, it is expected that for every 100 girls born, about 105 boys will be brought into the world.

But in findings researchers say indicates “systematic discrimination against females starts in the womb”, mothers within some key migrant communities are recording sons at rates of 122 and 125 for every 100 daughters in later pregnancies.

Lead researcher Dr Kristina Edvardsson from La Trobe University said it showed gender bias persisted in Australia, despite laws banning people from choosing the sex of their child, other than for medical reasons.

“We believe that some women may be terminating pregnancies after discovering they are expecting a girl and in other cases are travelling overseas to access non-medical sex selection services through assisted reproduction,” she said.

Analysing almost 1.2 million births in Victoria between 1999 and 2015, the study found while the overall ratio of male and female babies born was as expected (at close to 105 to 100), there were notable exceptions.

During 2011 to 2015, mothers born in China had about 108 boys to every 100 girls. The bias towards boys was much higher if they already had two or more children, with boys born at a rate of almost 125 to every 100 girls.

Similarly, mothers from India had boys at a rate of about 104 to 100 for their first child. But after their second child, this blew out to almost 122 boys to every 100 girls.

The rate of males born to mothers from some South East Asian countries was also more than expected.

Melbourne GP and president of the Australia India Society of Victoria, Dr Gurdip Aurora, said he had recently encountered one likely case of gender selection involving a couple who had migrated from India.

The pair already had three daughters, and the woman was pregnant again.

“They wanted to have an ultrasound done and [then] decide whether they would have the child or not, if it happened to be a female,” Dr Aurora said.

The GP refused to help them. He said when he saw the mother about six months later she was no longer pregnant.

“I checked with her and she said unfortunately we were holidaying in India and there was a miscarriage,” Dr Aurora said.

“I was pretty sure in my mind that it was a female and they aborted it.”

There is now widespread global access to ultrasound technology to determine the sex of a baby, and Australian parents can find out their baby’s gender from within 10 weeks with a newly-available blood test.

In India, Dr Aurora blames the entrenched preference for males on the country’s illegal dowry system, where people are often compelled to hand over large amounts of cash, goods or property when their daughters marry.

The Indian government has estimated that two million girls go “missing” from its population each year due to sex-selective abortion and other forms of discrimination that lead to premature death.

Yet this bias was not felt by all migrants, Dr Aurora said, and he believes gender selection is not a major issue in the Australian-born Indian community.

Dr Edvardsson said after some migrants arrived in Australia they had smaller families, which could mean they were more likely to turn to sex selection to have a son, as simply continuing to have children until a male was born was not a feasible option.

Gender selection through IVF is banned in Australia, except in cases where a child’s gender may help avoid the transmission of a genetic abnormality or disease.

There are, however, companies that provide gender selection through IVF to Australian parents who travel overseas, while abortion providers may have no way of knowing if a woman is seeking a termination due to a preference for a son.

A strong desire to have a child of a certain gender is not necessarily confined to select ethnic groups and many fertility service providers have called for governments to allow sex selection in Australia for the purposes of family balancing.

Dr Jim Tsaltas, a clinical director of Melbourne IVF, said there was support for the use of technology in cases where parents already had two of more children of the same gender.

Researchers will now embark on a bigger project investigating the causes and prevalence of prenatal sex selection across the country.