Americans headed to the polls in their millions for the 2018 mid-term elections to deliver crucial verdict on Donald Trump’s first two years in office.

But what are the mid-term elections and why are they important?

What were Americans voting for?

Midterm elections occur halfway through each four-year presidential term of office, with key seats in both the houses of the United States Congress up for grabs.

All 435 seats in the lower chamber House of Representatives and 35 of the 100 upper chamber Senate seats were at stake.

House of Representatives members serve two-year terms representing the people of a single constituency, while each state has two senators.

This year there were a record number of women on the ballot, which could significantly increase the number of women in elected office from a fifth of the 535 seats across both chambers.

There were also elections for 36 of the 50 state governors.

Around 250 million Americans are eligible to vote but turnout in mid-term elections is typically about 40 per cent.

This year, 114 million voters are believed to have taken to the polls.

The election marked the first nationwide vote since Russia targeted state election systems in the 2016 US presidential race.

Democratic Party takes back control

The Democrats took back control of the House of Representatives for the first time since the 2010.

Republicans had held a House majority since Barack Obama's first term as president. This year they retained control of the Senate.

The Democratic Party's victory over the House is regarded as a chance for the party to keep President Trump in check.

Their majority in the House will leave Mr Trump unable to pass key laws.

Record-breaking change

The results of yesterday's election saw a record-breaking 100 women elected to congress. 

In New York City Alexandria Ocasio-Cortez was elected the youngest ever congresswomen aged 29, while Ayanna Pressley became the first ever black woman elected to congress in Massachusetts.

In Michigan, Rashida Tlaib was the first Muslim woman and first Palestinian-American in office, while in Arizona, Democrat Kyrsten Sinema became the first openly bisexual senator.