Princess Kiko has developed complications with her pregnancy and will most likely give birth by Caesarean section, palace officials said Tuesday.

"We believe a Caesarean section will be needed at the time of delivery, which is highly likely to come earlier than expected," the palace doctor, Ichiro Kanazawa, said in a statement released by the Imperial Household Agency. He did not predict when the birth might be.

The princess, who is due to give birth in late September, has symptoms of partial placenta previa, a condition caused by some of the placenta dropping too low in the uterus, which can obstruct the baby's path during birth, according to Kanazawa.

"There is a high risk of early bleeding, infection or preterm birth triggered by the placenta previa," Kanazawa said. "To prevent these possible complications, the princess will have to rest for some time."

The doctor said both the princess and her baby, whose sex has not been disclosed, are in good health.

The pregnancy of the 39-year-old wife of Prince Akishino, who is the second son of Emperor Akihito, has captured national attention because the Imperial family has failed to produce a male heir to the throne since 1965.

Crown Prince Naruhito and his wife, Masako, have only one child -- Princess Aiko, 4.

Prime Minister Junichiro Koizumi began pushing for legislation to allow a woman to take the Imperial throne to resolve the succession crisis. But Princess Kiko's pregnancy announcement in February raised hopes for a male heir and Koizumi shelved the bill.