1 Yr Old Twin Sleep Troubles

Hello, my twin daughters are 13 months and just within the past week or so have begun waking frequently through the night. They were previously AMAZING sleepers...11+ hours a night, every night, with only waking maybe 1-3 times every once in a while during the night. They usually take 1 nap that lasts about a half hour to an hour although I don't force them...I just let them play until they're tired and they'll grab their little pillows and lay down. I've read stuff about nightmares/night terrors, separation anxiety, environmental changes, illness, etc etc etc. I'm currently 37 weeks and 3 days pregnant with our 3rd...but nothing has really changed in their routine yet...could they be sensing it or is it more likely something else? How should I handle this when I'm 2 weeks away from my scheduled c section?