Cross-border travel and commerce are developing too rapidly for meaningful enforcement, while prenatal technology is moving so far upstream it is possible to choose a male baby without claiming another life - or what most people would consider as a life. One of the most recent advancements allows sperm bearing the Y-chromosome which produces male babies to be sorted out before being implanted into a womb.
Enforcement is hard because patriarchal notions are so deeply embedded that women have taken up the cudgels against baby girls themselves.
"All my friends who went through abortions thought hard about it," says Mrs Nguyen Thuong Hoai, a receptionist in Ho Chi Minh City. "But they desperately needed sons, or…their husbands would try for sons with other women."
Over in Haryana, the president of Dhankar khap panchayat, Dr Om Prakash Dhankar, claims that the men are left in the dark.
"The women they have their own network and they do the tests and get the foetuses aborted," he says. "The men don't get to know at all."
In an environment where women are veiled in public, and held to blame - sometimes fatally - for not producing sons, they are likely doing it for their own survival.
Sometimes, supposedly remedial policies worsen the situation. In 2013, while partially relaxing its one-child policy, Beijing allowed rural couples whose first child was a daughter to try for a second, inadvertently affirming the bias for sons.
LAG EFFECT
The good news in China and India is that sex ratios at birth are dropping. In the 2010-2012 period, India registered a ratio of 110.13. During the next count in 2011-2013, the figure had dipped slightly to 110.01. China's ratio of 115.9 last year is a big climb down from 121.2 recorded 10 years ago.
In contrast, Vietnam's ratio has steadily deteriorated from 110.5 in 2009 to 113.8 in 2013. The country is being squeezed on both ends - while baby girls are being killed before birth, rural women are leaving for foreign grooms in thinly-disguised bride-buying arrangements.
Some parts of Vietnam now bear the same acutely lopsided sex ratios that afflicted China a decade ago: In the central Quang Binh province, the figure hit 129.6 in 2013.
"We have tried so much but can hardly change the mind and the culture of Vietnamese, who prefer sons to daughters," Dr Duong Quoc Trong, who heads the General Office for Population and Family Planning in Vietnam's Ministry of Health, was quoted saying last year in the online news portal VN Express.
"The sex imbalance now is so serious that Vietnamese men can hardly to get a wife in the near future, maybe from 2025 onwards."