WUHAN - Police have cracked a gang suspected of illegally offering ultrasound fetus gender tests in a car in Wuhan, in Central China's Hubei province, it was announced on Tuesday.

A 44-year-old woman surnamed Hu was arrested on March 29 after a pregnant woman reported she had received a fetus gender identification from her in a private car, said police with Wuhan's Bureau of Public Security.

According to the public report from Yunmen county, Hu's arrest is the most significant move in a crackdown on a gang of at least three people that operates by touring Wuhan with two ultrasound devices on the back seats of a car.

Introduced by middlemen, pregnant women in nearby regions are thought to have received the tests, which take only a few minutes.

It is suspected that Hu conducted the tests, while other gang members stood watch to make sure nobody approached the car.

Each pregnant woman paid 500 yuan ($79.3) for the test and 200 yuan to the middlemen.

While the case is still under investigation, police have also fined a man surnamed Peng 100,000 yuan after he confessed to acting as a middleman in the operation.

The pregnant woman, surnamed Wang, was attacked by Hu's husband and another four men as she left the police station on March 29 after making her report.

This is the third time Hu has been implicated in illegal fetus gender tests in the area, according to authorities with the Hubei Provincial Population and Family Planning Commission.

She was imprisoned for half a year in 2010 after being arrested and accused of running the tests for the second time.

With no certified medical qualification, she is thought to have mastered using ultrasound devices while a trainee nurse several years ago.

China's sex ratio at birth has increasingly skewed toward men since the 1980s, when ultrasound technology used for identifying the gender of fetuses became available. Though it is illegal in China for medical institutions or individuals to determine the sex of a fetus unless it is medically necessary, a black market has developed in the practise.

Amid China's one-child policy and traditional preferences for male children, many Chinese women have chosen to abort after learning they were carrying baby girls.

Numbers from the National Bureau of Statistics show that China's sex ratio of males to females at birth was 118.06 to 100 in 2010.

China adopted a family planning policy in the late 1970s to curb population explosion. The plan basically limits families to one child and encourages late marriages and childbearing.

"Illegal ultrasound fetus gender identification is blamed as the chief culprit for the sex ratio. And too-lenient punishment of the offenders is the direct reason," according to Shu Qinghua, director of the Yunmen County Population and Family Planning Bureau.