Think about it— she's a GRANDMOTHER. At minimum she's 40. Far more unlikely to be fertile now than she was when she couldn't have Ragnar's babies. They've done nothing to make Katheryn Winnick look 40, but the character must be. Travis Fimmel, on the other hand, looks like 5 miles of bad road. What happened to that…

As soon as Lagertha told Kalf she was pregnant, I knew he was dead meat. She's not pregnant, because if she could still get pregnant, she'd still be married to Ragnar and this would be a totally different (less interesting/less tragic) story.