Japan's Princess Kiko will give birth by Caesarean section on Sept. 6, the Imperial Household Agency announced Friday, amid speculation the Japanese royal family could produce its first male heir in four decades.

The gender of the baby has not been announced, but conservatives hope it will be a boy, thereby scuttling debate over whether to change Japan's male-only succession law to allow a woman to take the ancient Chrysanthemum Throne.

CountryWatch: Japan

Kiko, 39, was hospitalized last month in expectation of the surgery to have her third child. Doctors say she is in good health but shows symptoms of partial placenta previa, in which part of the placenta drops too low in the uterus.

Kiko is married to Prince Akishino, the second son of Emperor Akihito. A male baby would be third in line to the throne after Crown Prince Naruhito and Akishino.

Yuka Shiina, an agency spokeswoman, said the operation would take place Wednesday morning, but gave no further details.

The last male heir in the imperial family was Akishino, who was born in 1965. Naruhito and his wife, Masako, have a daughter but no son, meaning the family could face a crisis under Japan's male-only imperial succession law.

Prime Minister Junichiro Koizumi has said he favors changing a 1947 law to allow a female to assume the throne. The public also supports the change but government conservatives are opposed. The debate suddenly halted in February with the announcement of Kiko's pregnancy and the possibility of a male heir.

The last time Japan had a reigning empress was 1763, though the few women to have assumed the throne pre-1947 did so mostly as stand-ins until a suitable male could be installed.