Police said Wednesday that Tran Thi Ba, 28, was arrested following a police check of an apartment in Cao Thang District, Ha Long, a week earlier. Eight other women aged 24 to 35 were found in the room, three of them seven to 20 weeks pregnant.

An expanded investigation led to the arrest of Vu Nga Linh, 31.

Ba told the police she had rented the apartment for the eight women to be surrogates. The women, determined to be in good health, were transferred to the Quang Ninh Social Service Center for monitoring.

Vietnam legalized surrogacy in 2015 to benefit infertile couples, but not on a commercial basis. The rule is also that couples can only seek help from family members. Commercial surrogacy is punishable by up to five years in prison.

The country’s first baby born to a surrogate mother was in 2016 in Hanoi. The mother of the girl had been unable to conceive after 18 years of marriage due to congenital abnormalities.

In April, police in northern Vietnam arrested two women who ran an illegal surrogacy ring which took Vietnamese women to China to deliver babies.

For several years now, poor Vietnamese women have been lured to sell their newborns to China.

China, the world’s most populous country, suffers from one of the most skewed gender rates in the world due to its one-child policy and illegal abortion of female fetuses.

This has also been a major reason for the trafficking of Vietnamese women and girls over the border.