TOKYO - Japan's Princess Kiko, pregnant with a possible heir to the throne, will go into hospital on Wednesday, Kyodo news agency reported.

Japanese Princess Kiko, wife of Emperor Akihito's second son Prince Akishino, arrives at a memorial service for unknown soldiers at Chidorigafuchi National Tomb in Tokyo in this May 29, 2006 file photo. Princess Kiko, 39, is expecting her third child, raising hopes that a male heir may be born into the Imperial family for the first time in four decades. Japanese media had said last week that Kiko was likely to give birth through a Caesarean operation around Sept. 6, ahead of her late September due date, because of a complication in her pregnancy. [Reuters]

Japanese media had said last week that Kiko, 39, the wife of Emperor Akihito's younger son Prince Akishino, was likely to give birth through a Caesarean operation around September 6, ahead of her late September due date, because of a complication in her pregnancy.

No male has been born into Japan's imperial family since 1965, and the possibility that Kiko might bear a son has halted plans to revise a 1947 imperial succession law to give women equal rights to inherit the throne. Crown Prince Naruhito, the emperor's elder son, has one daughter, 4-year-old Aiko.