Debora MacKenzie, New Scientist, February 5, 2015

The Republic Day parade in New Delhi last week was the first ever attended by a US president. The visit was hailed as recognition of India’s growing geopolitical importance.

Besides the tanks and fighter jets, what the Obamas saw were women, including the country’s first all-female marching battalions, a woman leading the honour guard and a re-enactment of Indian women conquering Everest in 1993. “Congratulations, it’s a baby girl!” proclaimed a float.

The float celebrated Prime Minister Narendra Modi’s £10 million “Save the daughter” campaign, which aims to persuade Indian couples to stop selectively aborting female fetuses, a practice that some worry is already causing social instability in the country. Abortion is legal in India, but not on the basis of fetal sex.

Two days after the parade, India’s highest court ordered the Google, Yahoo and Bing search engines to stop adverts for providers of prenatal sex determination from popping up alongside online searches for the procedure. Next week the court is expected to order them to block adverts in the search results themselves.

Girls have long had a hard time in India. Infanticide was historically common, especially in north and west India, as girls were expensive to keep and required a dowry, while it was the sons who supported ageing parents. This had waned by the 1950s, but in the 1970s parents began to switch to prenatal sex selection, thanks to the availability of tests such as amniocentesis, and abortion. This accelerated in the 1990s, says Arindam Nandi of the Public Health Foundation of India, when ultrasound became available.

Using careful statistical analysis of the country’s census data, Prabhat Jha of the University of Toronto calculates that up to 4 million girls were aborted between 1991 and 2001, and a further 6 million by 2011. Most are aborted at five months–ultrasound at four months can detect the fetus’s sex. This could become easier with the next generation of prenatal testing, which requires only a blood test.

The search providers involved in the recent court case protest that they already comply with India’s advertising restrictions. “In India, we do not allow ads for the promotion of prenatal gender determination or preconception sex selection,” a Google spokesperson told New Scientist.

Searching for “ultrasound Delhi” in India led to a slew of ads for small clinics. None mention sex determination, but many have pictures of babies and offer other kinds of ultrasound tests. A search on “ivf boy Dubai” in New Delhi turned up adverts for clinics outside India that offer fetal sex tests and IVF babies of the desired sex. Both are illegal in India, but are increasingly the choice for the country’s elite, says Sabu George of the Centre for Women’s Development Studies in New Delhi, who filed the court case.

And you don’t need access to the internet. “You can get an ultrasound in villages that don’t have clean drinking water,” says Nandi. Technicians use code to tell parents what they want to know: buy pink clothes, say. “Everyone knows which clinics will tell you,” says George.

A look at the data from the 2001 and 2011 Indian censuses shows what has happened (see maps). Normally, human societies have 950 girls for every 1000 boys aged 6 and under. For India, the number of girls per 1000 boys was 927 in 2001, and 914 in 2011. This seems a small effect but Jha says that in such a populous country it equates to millions of aborted girls.

The practice is spreading. Skewed sex ratios are starting to show up in states such as Kerala, where female infanticide was not historically an issue but where ultrasound clinics are now common. “I fear it will be worse in 2021,” says George, when the next census is due.

Like all modernising societies, India went from some six children per woman in the 1960s to 2.4 now. “In the past, people just had children until they had the desired number of boys,” says Nandi. Now families planning only two children feel they cannot leave boys to chance.

Sex-linked IVF

Jha has found that in families where the firstborn was a girl, the second child was unnaturally likely to be a boy, with survey data from 1990 showing 906 firstborn girls per 1000 boys getting a little sister, and just 836 in 2005. If the firstborn was a boy, sex ratios among subsequent children were normal. “People say they just want balance in their families,” he says. “But they don’t abort second boys. Only second girls.”

The effect was greater the more wealthy and educated the family was. Now, says George, affluent couples are having IVF in Dubai or Singapore and choosing male embryos. Advances in prenatal testing will also make things easier and earlier. The Beijing Genomics Institute in China, as well as several US-based firms, have tests that sequence fetal genes from the mother’s blood in the first trimester.

The real issue, say George and other researchers, is one of human rights. But does a male-female imbalance also do social damage? An influential analysis in 2005 argued that societies with fewer girls and large numbers of unmarried men see more violence and instability. But some argue there is little evidence for this.

In India, recent research has suggested increased violence against women goes along with excess men, though this might be explained by increased crime reporting (see “Looking for a wife“). Either way, we need more studies of the impact of gender imbalance, says Sanjay Zodpey of the Public Health Foundation of India. “But we shouldn’t wait to measure the impact before we stop this happening.”