Thank you for downloading this edition of The Witness History Podcast from the BBC World Service, with me, Josephine McDermott.

Today I'm taking you back to 1994, when India passed a key law to stop couples expecting a baby from being able to find out the sex of that child.

To understand the problem, you have to understand the centuries-old desire for boys in India. They're considered assets, future breadwinners for the household.

Manisha Gupta was born in a society where she says people saw girls as unintended errors in the pursuit of sons.

But in the 1980s techniques were developed which made it possible to know the sex of your baby before birth and actually avoid those so-called errors.

In 1990, the BBC filmed a doctor performing an ultrasound examination on a pregnant woman in Delhi using high-frequency sound waves and images created on a screen of the child the woman is carrying.

This patient already has three daughters.

Do the legs and that's the sex organ. You can quite clearly see that it's a girl.

As with other women who discovered they are carrying daughters, she is in no doubt about her response.

She says she will have an abortion.

Its consultations like this, which have meant that over the last 50 years, an estimated 46 million girls have not been given the chance to live.

The amount of cases that we do in our two clinics where we do perform sex determination is roughly 100 a month.

And I see only an increasing trend to my dismay that people are still wanting more and more of this test.

This is what Manisha has dedicated her career to challenging.

My family had a history of being part of the Socialist Party and so automatically while we were fighting for people's right to housing and people's right to health, gender discrimination and patriarchy were also very, very major concerns.

It was 1980 when Manisha was in her early 20s that she and others in the feminist movement realized how popular the new sex determination tests were becoming and what couples were doing with the information.

In Bombay women's group was called by a multinational company.

They came and said that people are putting up bills for a test that has never been performed before and some of these then are also followed with abortionists as part of the family health insurance.

Couples were finding out the sex of their unborn babies and having abortions if they were having a girl.

As feminists we knew that technology isn't the cause of discrimination but in this case technology was being used to further gender discrimination.

Some wantedness and not unwantedness always existed but this technology actually made it possible.

At the same time we were also seeing hoardings in the north of India saying better 5,000 now than 500,000 later meaning that you know pay for the test now and save upon dowry a few years later.

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