I had a request to put up a post where you guys could talk about how you're dealing with or not dealing well with the 9-month sleep regression.
To recap, this is the period encompassing the developmental leap at week 37 and the one at week 46. Very very often there's also some teething mixed in there, and learning to crawl and/or pull up and/or cruise and/or walk.
Which means you've got a brain working on developmental stuff that won't let the kid sleep, a brain and body working on movement that won't let the kid sleep, and maybe some random shooting or throbbing gum and jaw pain in there, too.
In other words, you're going to have to accept that the kid just can't sleep straight through until some of this is over with.
(We haven't even mentioned how this sleep regression can affect other stuff, too, like naps and mood and clinginess and what they'll eat and won't eat. Some kids who keep sleeping at night just wig out during the day--that's their particular reaction to the developmental spurts.)
Which means your plan shifts from Get Kid To Stay Asleep to Maximize Sleep For Everyone Else. This is not the time to pretend you know what's going on or that you have it all under control. This is not the time to say "your job is this and mine is that." It's the time to divide up the schedule so everyone gets 5 hours at a stretch if possible. If one of you has to go to sleep at 8 pm and take the 8-1 shift so the other has the 1-6 shift, do it.
Here are the important things to remember: Lots of us have been through it. You will get through it. There is nothing inherently wrong with your child--this is normal. Hideous and demoralizing, but normal. You're doing a good job.