Kim Kardashian and Kanye West [Photo: Courtesy]

Kim Kardashian and Kanye West's surrogate is in labour with their fourth child.

The Keeping Up With The Kardashians stars are expecting a baby boy and TMZ has reported that he is on his way, though it is uncertain how far into the labour they currently are.

On January 15 it was a year since Chicago was born and there were plans to use the same surrogate mother for baby number four.

A spanner was thrown in to the works though, as the original surrogate became pregnant with a child of her own and this has ruled her out of carrying another of the reality star's offspring.

Reality star Kim and rapper Kanye used a leftover embryo from when Chicago was conceived for a surrogate.

Kanye West and Kim Kardashian  [Photo: Courtesy]

A source has told People at the time that the pair had, "hoped to work with the same gestational carrier," but after that didn't work out, they are now, "working with a second carrier now that is pregnant and will give birth in the spring.”

It is believed that 38-year-old Kim had a very 'hands on' approach to this pregnancy and, "is very involved with the carrier."

The woman is apparently local to Kim and Kanye, 41, and they have made sure the surrogate "had everything she needs," while Kim 'went to doctor's visits with her' to ensure that the pregnancy went as smoothly as possible.

It is dangerous for Kim to carry another child after she suffered from a placenta accreta after the birth of son, Saint.

Kim Kardashian and Kanye West [Photo: Courtesy]

This is when part or all of the placenta remains connected to the uterine wall after childbirth and affects just three in 1,000 pregnancies.

The new born will join three siblings in five-year-old North, Saint, who is three and one-year-old Chicago.