Taro Aso, policy chief of the ruling Liberal Democratic Party, said he thinks it is too early to consider revising a male-only inheritance law for the Imperial family to allow a woman to ascend to the throne.
The Crown Princess is expected to give birth in late November or early December.
"We must think about (the revision) if no male is born. But at this point, when we do not know which it will be, we are not yet at a point to assume that no (boys) will be born in the future," Aso said Wednesday. "We have no plans to touch the Imperial House Law at this stage."
If the 37-year-old Crown Princess gives birth to a boy, he will be the second in line to the Imperial Throne after his 41-year-old father, the Crown Prince. The Crown Prince's younger brother, Prince Akishino, will remain next in line if the baby is a girl.
The possibility that it may be a girl has prompted talk about changing the law to allow Japan to have a reigning empress.
Promulgated in 1947 and implemented in 1948, the law stipulates that only a male member of the Imperial family can ascend to the throne.