Conservatives within Japan's hidebound imperial household must be rejoicing at what must seem a miracle pregnancy.
By Sarah Buckley
If Princess Kiko had a boy, he would be third in line to the throne
News that Princess Kiko, the 39-year-old wife of the emperor's second son, is expecting a child in the autumn may save them from their worst fear - the prospect of women ascending the Chrysanthemum Throne.
For months Japan has witnessed a mounting debate over whether the Imperial Household Law - which allows only male heirs - should be amended.
With no male heir born into the imperial family since 1965, supporters of change looked to have nearly won the argument.
But Princess Kiko's pregnancy has at least stalled the process, and even - if she gives birth to a boy - ended it for some time.
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
Prime Minister Junichiro Koizumi, who had pledged to get the succession law changed by the end of Parliament's current session in June, has turned more cautious.
"It's desirable that the legislation be enacted when everyone can support it," he said on Wednesday, one day after news of Princess Kiko's pregnancy caught Japan by surprise.
By Friday he had gone further, after Japan's media reported that he had shelved the plan.
"We should make a decision after having a clearer grasp of the situation," he told reporters. "I don't think the issue should trigger political conflict"
Mr Koizumi's turnaround suggests that he may no longer be willing to take on powerful, conservative forces opposed to female succession.
News of the princess' pregnancy - which is still in its earliest stages - was probably leaked by an imperial household member.
The fact the source was willing to risk going public so soon may indicate how desperate some royal officials are to scuttle the succession law debate.
Christopher Hood, director of Cardiff University's Japanese Studies Centre, said he thought Mr Koizumi was more likely to have been influenced by opposition within his own Cabinet than from the Imperial Household.
There is intense media interest in the story
The Japanese public seems broadly supportive of letting women take the throne, according to opinion polls.
But politicians in Mr Koizumi's ruling Liberal Democratic Party (LDP) appear more divided, with several Cabinet members making less than positive comments about the proposed change in recent days, including government spokesman Shinzo Abe and Foreign Minister Taro Aso.
Both men are potential successors to Mr Koizumi, who has said he plans to step down as LDP leader in September.
Mr Koizumi may be worried that pressing ahead with the politically controversial change could tie his hands on other reform plans he may have for his last few months of power.
"This is linked to the LDP succession crisis, never mind the royal succession crisis," Mr Hood said.
Reports say that Princess Kiko is only about six or seven weeks pregnant, and so it should be possible to determine the sex of her baby in about 10 weeks time, by the end of April - before the Parliament's session ends in June.
If the baby turns out to be a boy, support for changing the law would quickly dwindle. If a girl, Mr Koizumi might just have time to introduce a bill, but he may not want to risk such a rush.
Princess Kiko's pregnancy could therefore have ended the debate before it even reached parliament.
It is easy to assume that opposition to change, in a male-dominated society such as Japan, is rooted in a fear of empowering women.
But analysts argued this was not the case.
"I always thought that it's nothing to do with gender equality," said Hiroko Takeda, lecturer at Sheffield University's School of East Asian Studies.
She said it had more to do with preserving Japan's traditions, with the monarchy's hierarchy at its heart.
"The gender issue isn't important in this," agreed Ichiyo Muto, president of the People's Planned Study Group, an organisation which studies alternative political and social systems.
He said conservatives recognised the need to shore up the monarchy by sorting out the succession issue. One member of the royal family, Prince Tomohito, has suggested expanding the royal circle to include more potential male heirs, and even reintroducing concubines.
But Mr Muto said the conservatives' overriding concern was to proceed cautiously, given the enormity of the change.
"They at least want to resist the kind of easy attitude with which Koizumi brought it up," he said.
If Princess Kiko does give birth to a boy in the autumn, it provides an easy solution to the succession, at least for another generation.
But it does not mean Japan can avoid the debate forever.
"If the boy dies in some accident, they still haven't a clear policy on who comes next," Mr Hood said.