Jennifer Lopez wants to have a baby with Casper Smart.

The 43-year-old 'Dance Again' singer - who has five-year-old twins Max and Emme with her ex-husband Marc Anthony - has allegedly turned to IVF in the hopes of getting pregnant with the 25-year-old back-up dancer.

A source said: ''She's scared that time isn't on her side with regards to her age. But she's hoping that with fertility treatments she'll be pregnant in the next couple of months.''

The couple reportedly put their plans to wed on hold because they couldn't reach a prenuptial agreement, and are now focused on having a baby.

The source told the US edition of Star magazine: ''They argued constantly over it, but Jen has decided to let the issue go and put her trust in him. She's more interested in trying for a baby than planning a wedding right now anyway - and Casper is completely on board.''

The singer wants to keep her fertility treatments a secret and Casper has agreed they will both act surprised when they announce she is pregnant.

The insider added: ''She's paranoid about people knowing about her pregnancy hardships, because it makes her feel old.

''He loves Jennifer and he knows he's set financially for life if she has his baby. They made a deal that when the pregnancy happens, Jen will make it sound like an 'oops' and a blessing at the same time, even though she's actually planned the whole thing.''