This statement just in from Iowa Democratic Party Communications (IDP) Director Mandy McClure, explaining the delay in the results.

"The integrity of the results is paramount. We have experienced a delay in the results due to quality checks and the fact that the IDP is reporting out three data sets for the first time.

"What we know right now is that around 25% of precincts have reported, and early data indicates turnout is on pace for 2016."

Gary O'Donoghue
BBC News, Des Moines

Results coming soon: this is the understatement of the night.

The Democratic Party in Iowa is clearly having problems with its technology. The precinct chair in Norwalk 1 in Warren County told me she had given up trying to use the new results reporting app and was just going to ring them in.

Image source, Photo by Darlene Hammond/Hulton Archive/Getty Images

The BBC's Christian Fraser just pointed out on air in Iowa that Pete Buttigieg is younger than former child star Macaulay Culkin - star of holiday movie Home Alone (with a sequel, of course, that featured Donald Trump).

The mayor of South Bend is 38 years old - just three years older than the 35-year-old age minimum required for presidential candidates in the US.

So who else is older than Mayor Pete?

• Shakira, 43
• All of the Spice Girls
• Kim Kardashian, 39
• Christina Aguilera, 39
• Justin Timberlake and all the rest of boy band NSYNC
• Every member of the Backstreet Boys

• Britney Spears, 38 (by a month)

Image source, Kevin Winter/Getty Images for iHeartMedia

The results sure are taking their sweet time to be announced.

Democratic party officials in Des Moines confirm that the results are rather slow to come out, but this is due to "quality control", they say.

“We are doing our quality control checks, making sure the numbers are accurate. People are still caucusing, we’re working to report results soon," they've told reporters.

Helier Cheung
BBC News

The Iowa Democratic Party's handbook uses coin tosses to resolve ties, and we've already seen that happen a few times tonight.

This typically happens when two candidates have the same number of supporters but there's an odd number of delegates. The coin toss determines who gets the extra delegate.

It may sound arbitrary, but a lot of states use similar methods - in Nevada's Democratic caucuses, ties are broken by whoever draws a higher card from a deck of cards, while in Mississippi, a state election tie was resolved by drawing straws.

In 2016, there were conspiracy theories, external after reports that Hillary Clinton won six coin tosses in Iowa - although experts pointed out that her rival Bernie Sanders also won several coin tosses, external, and that mathematically, the number of delegates won through coin flips was not significant.

The coin toss was "a party rule that they put in, thinking it would be rarely used - but it ended up being used a lot, which is a testament to how close Sanders and Clinton were," says Prof Kedrowski.

Here are eight other unusual things about the Iowa caucuses

But we'll keep you entertained until they arrive.

The BBC's Anthony Zurcher is on a working farm in Urbandale, Iowa, where Amy Klobuchar and Pete Buttigieg have both done very well - coming out on top along with Joe Biden.

According to an analysis by Kantar Media/ Campaign Media Analysis Group (CMAG), here's how much the candidates have spent on TV and Radio ads in Iowa:

• Tom Steyer: $16.3m
• Bernie Sanders: $10.8m
• Pete Buttigieg: $10.5m
• Andrew Yang: $6.9m
• Elizabeth Warren: $6.3m

• Joe Biden: $4.2m
• Amy Klobuchar: $3.9m
• Michael Bennet: $1.1m
• Tulsi Gabbard: $258,630

It wouldn't be a US election without baby-kissing.

Here's a selection of some of the best moments between politicians and babies in the final days before the Iowa caucuses.

Image source, Getty Images

Image source, Getty Images

Image source, EPA

Image source, Getty Images

Gary O'Donoghue
Warren County, Iowa

Caucuses give the true meaning to the phrase "vote with your feet".

And about 200 people did just that in Norwalk 1 precinct in Warren County, eight miles outside Des Moines.

Candidates here needed 30 votes to make the 15% threshold, and, tantalisingly, Amy Klobuchar was on 29 after the first round.

There was a tense 15 minutes when everyone watched to see if her 29 votes could be redistributed around the room; but then at the last minute, Drennan Fischer, who had stood under Michael Bloomberg's sign, was wooed by six or seven of Senator Klobuchar's supporters.

With time almost up, she walked the few yards across the floor and gave the senator from Minnesota the one crucial vote to earn her a delegate.

They whooped with joy - even if afterwards, Ms Fischer was far from confident that the Klobuchar candidacy would survive the night.

The final tally from Norwalk:

Pete Buttigieg 48

Joe Biden 47

Bernie Sanders 33

Elizabeth Warren 31

Amy Klobuchar 30

It sounds dramatic - and it kind of is.

The "realignment" phase of the Iowa caucuses has started. This means that any candidate who hasn't reached the viability threshold (normally around 15% of voters) can shift their support to another candidate.

Supporters of the remaining, viable candidates have a second chance to make their pitch to voters looking for another person to give their support. This reshuffling can swing the final vote count considerably.

Still a bit confused? Let’s show you how it works using empty chairs.

Over to you, Katty Kay and Christian Fraser in a barn in Des Moines.

Helier Cheung
BBC News, Washington DC

We said it earlier but it bears repeating: there will be several sets of results tonight, so more than one person could spin themselves as the winner.

Iowa will report on the first round results – so everyone’s first choice – as well as the final results after supporters of weaker candidates have realigned themselves to other candidates. And there’s also the number of delegates awarded to each candidate.

Finally - whoever gets a bigger vote share than expected could also argue they’re the winner, says Karen Kedrowski, a political science professor from Iowa State University.

“My dark horse candidate who could win without winning is Amy Klobuchar - she’s consistently fifth, but she’s worked her tail off in the state, going to all the counties, and she’s from a neighbouring state. If she breaks into the top four, she might be the surprise winner even if she doesn’t come in first.”

We've eaten quite a lot of pizza here in the office in Washington tonight, so forgive us for trying to explain what is happening in Iowa using our leftovers...

The BBC's Chris Buckler is at Elizabeth Warren's campaign HQ in Iowa, where he's been reviewing entry polling data.

The majority of caucus-goers are women, according to a CBS poll.

This could be good for either of the female candidates, Elizabeth Warren or Amy Klobuchar who comes from the neighbouring state of Minnesota.

One third of voters say they've only made up their mind in the past week.

Considering how many visits the candidates have been making to Iowa in the past month, it is remarkable that Iowans are only just deciding, adds the BBC's Katty Kay in Des Moines.

Image source, Getty Images

As results from Iowa trickle in, you're going to start hearing more about delegates. So what are they?

Delegates are key to the caucus results: the more votes a candidate gets in a caucus, the more delegates they are awarded. Those delegates then vote for that candidate as the party's nominee for president in the summer convention.

The number of delegates in each state differs. Out of a total of Democratic 3,979 delegates, Iowa lays claim to 41, while California has a whopping 415 delegates up for grabs this year.

During caucus and primary season, if any one candidate wins more than 50% of those delegates (that's 1,990 delegates), then they become the nominee in a vote at the Democratic convention this summer.

The BBC's North America Editor Jon Sopel is at the Bernie Sanders HQ in Iowa tonight.

He says the event might be called a campaign watch party, but it's "one of those parties where you're first to arrive and no one has uncorked the wine yet".

Sanders has spent more in Iowa than anyone else, he notes, and is certainly being considered a front-runner.

"You don't win the nomination by winning the Iowa caucus but you can sure as hell lose by doing really badly. And that's not happening for Bernie tonight," says Jon.

In 2016, Jon was in Iowa with Sanders where he says his message was much more about starting a "revolution" - more of a "left-wing offering".

"But this year its more about beating Trump and elect-ability."

Marianna Brady
BBC News, Des Moines

The final numbers are in here at the Des Moines Community Playhouse caucus.

Pete Buttigieg, Elizabeth Warren and Bernie Sanders are viable.

46 people for Pete Buttigieg (one delegate)

85 people for Bernie Sanders (two delegates)

103 people for Elizabeth Warren (three delegates)

Four uncommitted, including our friend Andrew. “It didn’t really end up mattering," he said.

We may have the results from across Iowa soon as well...

Marianna Brady
BBC News, Des Moines

One of our undecided voters - Andrew - is the last one in the Des Moines Community Playhouse auditorium to decide. Warren, Sanders and Buttigieg volunteers are surrounding him trying to convince him to come join them.

Elizabeth Warren and Bernie Sanders were viable with a large margin in the first round, and Pete Buttigieg was able to convince enough Amy Klobuchar and Andrew Yang supporters to join them – so he became viable in the second round.

It still remains to be seen who Andrew will choose to support.

Our other undecided voters have made up their minds. Here’s what they said:

Tim

I’m going to go to Warren. After the Amy Klobuchar people started breaking up and being convinced to go to other candidates, I chose Warren. I took a poll a while back and learned that my values most aligned with Klobuchar, but Warren was a close second. Yang wasn’t viable either so there’s no point going to him. Warren it is.

Samantha

I chose Bernie. I didn’t feel like anyone else made a strong enough pitch to me about why I should come stand with them. Only one person came and talked to me to try and sway me, so I’m here with Bernie.

You may have noticed we're talking a lot about Iowans congregating in corners of gyms, theatres and churches all across the state.

So what are they actually doing?

At 1,779 precincts (districts) throughout Iowa, voters are meeting to caucus at a predetermined caucus location.

Voters are moving around the caucus site, congregating in a particular part of the meeting room corresponding to their preferred candidate.

At most Iowa caucus locations, a candidate must get support from at least 15% of voters to achieve viability. If a candidate isn't viable, his or her supporters will likely be recruited by the supporters of other candidates.

AP News projects that Trump has (predictably) won Iowa.

He was up against two other Republicans, but due to his overwhelming support from the Republican party, it had been considered a foregone conclusion that he would win.

We still have hours to go until we know who Iowa Democrats want to take him on in November 2020.