Jennifer Aniston and Justin Theroux

Jennifer Aniston and Justin Theroux

Jennifer Aniston is reportedly pregnant.

The 45-year-old actress is rumoured to be expecting her first child with fiancé Justin Theroux, 43, but friends believe she doesn't want to officially announce the news because she's worried about complications.

A source told the US' OK! magazine: "The buzz in Jen's inner circle is that she's nearly three months along but doesn't want the news to come out until she knows for sure that the baby will be okay."

The former 'Friends' star has been dating Justin since 2011 and was reportedly thinking about her chances of having a baby six months into their relationship.

The source explained: "Jen started having fertility treatments six months into the relationship. She knew the older she got, the harder it would be to get pregnant, so she had her eggs frozen.

"With regular attempts at in vitro fertilisation, she was hoping to get lucky, but she didn't dare think about it too much because of the chance for disappointment."

However, last year, the blonde beauty indicated that she didn't have an overwhelming desire to experience motherhood because she's content with her life as it is.

She said previously: "I surround myself with my amazing work, my amazing friends, my amazing partner, my beautiful dogs, and I tune that noise out. I mean, I think it's very sweet that people want everything for me, (but) I'm so content and happy."