Chinese and American scientists have sequenced and analyzed a portion of genomes collected from more than 140,000 pregnant women of different ethnicities throughout China in one of the largest genetic analysis projects of the Chinese people to date.

The study looked at 141,431 participants, including 36 of China’s 55 ethnic minority groups. Among their key findings published on Thursday in the scientific journal Cell is the association between genes and the birth of twins.

Researchers at a bioscience and genome sequencing laboratory in the southern Chinese city of Shenzhen used data from non-invasive prenatal testing to sequence randomly 6 to 10% of each participant’s genome.

Xu Xun, the center’s lead scientist and one of the co-authors of the paper, told Xinhua that even though non-invasive prenatal testing belonged to the category of low-pass sequencing, their study could still be of statistical significance as their huge chunk of data was collected from a large base of participants.

Such a test to sequence small amounts of a pregnant woman’s cell-free DNA to screen for fetal trisomy has become popular in China, with approximately 6 to 7 million tests done each year, according to Xinhua.

Xu’s team found that the variation in a gene called NRG1 was linked to a greater chance of having twins.

Their proof-of-concept analyses allowed scientists to identify patterns in the evolutionary history of China’s different ethnic groups, to pinpoint novel genetic loci linked to phenotypes like height and body-mass indexes, and to identify viral DNA distributions specific to the Chinese genome, according to the paper of the study.

The researchers also found that many Chinese had genetic variants common among Indians and Southeast Asians and people living along the route of the ancient Silk Road, likely due to the result of thousands of years of intermarriages.

Also, DNA sequencing in maternal blood revealed links between viruses and genes that determine susceptibility to diseases. For instance, a variation in one gene was associated with a higher concentration of herpesvirus 6 in a mother’s blood.

Herpesvirus 6 is the most common cause of the relatively benign baby rash called roseola, but a high “viral load” correlates with more severe symptoms. People with Alzheimer’s disease also have higher levels of herpesvirus 6 in their brains.

Another team led by Rasmus Nielsen, a professor of integrative biology at the University of California, Berkeley, oversaw the computational analysis performed by their Chinese partners.

“We’re excited about the volume [of more than 140,000 participants]: our participants represent 1/10,000 of the Chinese population, so it really is a large sampling and a good reflection of the entire population,” said another co-senior author Jin Xin with the Guangzhou-based South China University of Technology.

Their next step is to examine the genes of one million Chinese women.