Shenzhen Customs says it has trained its staff and tightened checks on the illegal transportation of blood samples to Hong Kong for gender screening, which is banned on the mainland.

It took these actions shortly after a woman was caught on Aug 7 carrying 96 human blood samples in her bag when passing through the Luohu checkpoint in Shenzhen for Hong Kong.

The samples are believed to have been from pregnant women and were being taken to Hong Kong for DNA gender screening.

"It is the first case that customs in the city have seized blood samples going from Shenzhen to Hong Kong without advance declaration," Cui Chao, a press official with Luohu Customs, told China Daily.

The blood samples, contained in glass test tubes with a capacity of about 12 milliliters each, were all marked with names and accompanied by two documents - one for an ultrasound, giving information such as gestational weeks and size of the fetus, and a signed agreement for a DNA test - according to customs.

The carrier, surnamed Lin, told customs official she was only employed to take the blood samples to Hong Kong. In return, she earned HK$300 ($38.70) for each trip.

Lin was taken to the local inspection and quarantine authority, along with the blood samples for further tests, Cui said.

However, local media reported that a mature business has developed over the past two to three years in Shenzhen, which helps mothers-to-be across the country learn the gender of their babies at an early stage of their pregnancy, best at seven to eight weeks, by sending blood samples to Hong Kong for DNA tests.

The mainland, where abortion is legal, has banned gender screening to achieve gender balance under its prevailing family planning policy, which has just been relaxed to allow couples where either spouse is from a one-child family to have a second child.

According to a report by Shenzhen Evening News, an agent in Shenzhen said more than 10,000 clients paid for the service in a month, and some were even from distant areas such as Beijing and the Inner Mongolia autonomous region. The agency charges at least 4,200 yuan ($683) for each test.

Wu Qiong contributed to this story.

Contact the writer at [email protected]