GIFU (Kyodo) House of Representatives lawmaker Seiko Noda filed her marriage to her common-law husband with local authorities after giving birth to a baby boy last month through artificial insemination after years of fertility treatment, her office said Wednesday.

The husband of the 50-year-old Noda had conveyed his hope to be registered as the baby's father and changed his last name to Noda, according to her office.

As Noda is a major advocate of a system to allow married couples to have separate surnames and current law stipulates that married couples should have the same surname, she had opted not to officially register her marriage.

Noda, a former post, telecommunications and consumer affairs minister, wanted to "defend at all costs" her family name, as she is the "daughter and heir" of the Noda clan, she said on her official blog.

"My husband respected my will . . . so I will be able to remain Seiko Noda," the Liberal Democratic Party lawmaker said.

Noda, a six-term Lower House member who was once touted as a potential candidate to become the first female prime minister, once had a de facto marital relationship with LDP House of Councilors member Yosuke Tsuruho.

They did not officially register their marriage as Tsuruho also wanted to keep his surname, Noda said on her blog. The two ended their five-year relationship in 2006.

Last year, Noda became pregnant after undergoing artificial insemination in the U.S.