The revelations threatened to steal any remaining thunder from Day One of the Republican National Convention, which already was overshadowed by Hurricane Gustav - and brought unwanted attention to the 44-year-old governor, who has little experience on the national stage.
The Republican convention, taking place just three days after McCain named Palin as his running mate, had already been scaled back because of the hurricane. Coming after the randomness of Gustav, the revelations added to the sense of unscriptedness hanging over the convention.
"Life happens," said McCain adviser Steve Schmidt, talking about the pregnancy story.
"An American family," added colleague Mark Salter.
In a brief respite from partisanship, Democratic rival Barack Obama weighed in: "I think people's families are off limits and people's children are especially off limits."
Obama also emphasized that his campaign was not in any way responsible for the spreading of any of the Internet rumours surrounding Palin and her daughter.
"If I ever thought that there was somebody in my campaign that was involved in something like that, they'd be fired," Obama said.
McCain aides said the announcement about the pregnancy of Palin's daughter, Bristol, was aimed at rebutting Internet rumours that Palin's own youngest son, born in April, was actually the daughter's.
The national convention, which a political party counts on to send its candidate surging into the fall campaign, already had been relegated to a distant second to the hurricane on TV, in newspapers and on Internet Web sites.
The pregnancy statement, attributed to Sarah and Todd Palin and released by the campaign, said that Bristol Palin would keep her baby and marry the child's father, identified only as a young man named Levi. The baby is due in late December.
"Our beautiful daughter Bristol came to us with news that as parents we knew would make her grow up faster than we had ever planned. We're proud of Bristol's decision to have her baby and even prouder to become grandparents," Sarah and Todd Palin said in their brief statement.
Palin had told McCain's team about the pregnancy during lengthy discussions about her background, aides said. At several points, McCain's team warned Palin that the scrutiny into her private life would be intense.
Prominent religious conservatives, many of whom have been lukewarm toward McCain's candidacy, predicted that the announcement would not diminish conservative Christian enthusiasm for the vice presidential hopeful, a staunch abortion opponent. In fact, there was talk that it might help.
As for the Alaska probe, a Republican-dominated legislative committee is investigating whether Palin dismissed Public Safety Commissioner Walt Monegan after he refused to fire a state law enforcement official who had divorced Palin's sister.
The state's attorney general, Talis Colberg, hired Thomas V. Van Flein more than two weeks ago to represent Palin and members of her staff, according to Van Flein. He has represented the Palin family in the past as a private attorney, according to a McCain aide who spoke on condition of anonymity because he was not authorized to discuss the matter publicly.
Van Flein said he couldn't confirm representing the family in the past because of attorney-client privilege.
"Did I know the Palins before the state hired me? Yes," he told The Associated Press.
"The governor of every state gets legal counsel, and this attorney is part of a weeks-old effort to provide this governor defense in a series of outlandish, politically motivated charges," said senior McCain adviser Tucker Eskew.
"It is a matter of her job and is not recent, and it is not related to her selection on the McCain-Palin ticket."
Palin's decision to hire the attorney was disclosed by the Legislature's investigating committee, which released a message it had received from her new lawyer on Friday.
In St. Paul, the convention opened on time, though the opening-day session was shortened because of the hurricane. From the convention podium, Republcian officials asked delegates to take out their cell phones and text-message contributions to help in the relief effort.
McCain's wife, Cindy, and first lady Laura Bush made their own appeals for relief help in the convention hall later in the day.
The delegates approved the party platform and other business, but most of the opening-day speeches - all of which had been expected to acclaim McCain and assail Obama - were scrapped.
Palin was in Minnesota preparing for her Wednesday night nomination acceptance speech when the campaign released the pregnancy statement; her family was home in Alaska.
"Bristol and the young man she will marry are going to realize very quickly the difficulties of raising a child, which is why they will have the love and support of our entire family," the parents said.
The campaign said it was not disclosing the father's full name or age or how he and Bristol knew each other, citing privacy.
Sarah Palin's fifth child, a son named Trig, was born in April with Down syndrome. Internet bloggers have been suggesting that the child was actually born to Bristol Palin but that her mother, the 44-year-old Alaska governor, claimed to be the mother.
Palin spokesman Bill McAllister emphatically denied those rumours, and McCain adviser Mark Salter said the campaign announced the daughter's pregnancy to rebut them.
"Senator McCain's view is this is a private family matter. As parents, (the Palins) love their daughter unconditionally and are going to support their daughter," said McCain spokesman Steve Schmidt.
Reaction from religious conservatives was sympathetic.
Focus on the Family founder James Dobson issued a statement commending the Palins "for not just talking about their pro-life and pro-family values, but living them out even in the midst of trying circumstances."
