I'm not sure what all you want to hear so I'm going to put everything in a spoiler highlight and you can chose.
[SPOILER]She says that she is pregnant but there could be a problem with the pregnancy and she could not live. If you want to kno more go to next spoiler[/SPOILER]
[SPOILER]Causes some fighting between the two as Lucas does not want to lose payten and she wants to get married so she will be married if she dies. Lucas says no. Soon enough Lucas says ok and they get married. When Lucas brings Peyton home she starts bleeding and passes out. She goes into labor has the baby and is in a coma and soon comes out of it.[/SPOILER]
I put it in two spoilers as I didn't know if you wanted just the answer to your question or more.
"Sanity? Worthless things like that, I never had them for as long as I can remember!"