They gave them a cash award of VND1.49 million ($64) and a certificate as part of a policy that seeks to reverse a gender imbalance that has been worsening for years.
Hau Giang, the largest sugarcane farming area in the Mekong Delta, has a population of nearly 730,000.
Its fertility rate is 1.34 children per woman against the national rate of 2.09 children, which puts it in a list of 21 provinces and cities with the lowest rate in the country.
Its sex ratio at birth is 110 boys per 100 girls while the "natural" or "normal" ratio is 105-106.
In 2018 authorities earmarked nearly VND18 billion ($760,000) to implement the family planning policy in 2019-25.
Besides rewarding couples who have two daughters [and no other children], it also gives VND3 million ($128) to those who have no more than two children for three years and VND5 million ($214) if it is five years.
Vietnam has had a maximum two children per couple policy since the 1960s, but the government is now encouraging families to have two children instead of just one.
The sex ratio at birth is a high 111.5, according to the General Statistics Office.
Vietnam will have 1.5 million more men than women aged 15-49 by 2034 if the sex ratio imbalance remains unaddressed, a survey by the office found.
The main cause of the gender imbalance is people’s preference for boys over girls since Vietnam is still heavily influenced by Confucian values, including patriarchy, which favors males over females in family matters and social settings as men are responsible among other things for carrying on the family lineage and worshipping ancestors, experts said.