Japan's Princess Kiko has gone into hospital in Tokyo to prepare for the birth of her third child.
Princess Kiko arrived at hospital with her husband Prince Akishino
The wife of the emperor's second son has had complications during pregnancy and is expected to give birth by caesarean section in early September.
The pregnancy is attracting enormous attention from the Japanese public, many of whom are hoping for a boy.
Current law allows only males to ascend the throne, but the emperor's children have yet to produce a male heir.
Currently only males can ascend the Japanese throne
Emperor Akihito has two sons, Naruhito and Akishino
If Naruhito died without a male heir, Akishino succeeds
His wife, Kiko, is now pregnant
Princess Sayako married a commoner so her children cannot ascend throne
Crown Prince Naruhito and his wife, Princess Masako, have a daughter, Aiko. The Emperor's third child, Princess Sayako, married a commoner and so her children would not be able to ascend the throne.
Doctors said last month that the 39-year-old Princess Kiko had symptoms of partial placenta previa, a condition in which part of the placenta drops too low in the uterus.
Officials were quoted as saying she was expected to give birth by caesarean section on or around 6 September, a couple of weeks ahead of the due date.
The princess arrived with her husband Prince Akishino at the hospital in Tokyo, bowing her head and smiling at reporters as she was driven inside.
The imperial household said in a statement on Tuesday that the princess had been resting at home, but would go into hospital to "ward against the possibility of premature bleeding and to prepare for delivery".
"The princess's pregnancy is progressing well and the baby is developing normally," the statement added.