What do I use to keep an infant warm in a crib?

You do use a blanket by swaddling them. Other than that warm outfits help.

My daughter hated being swaddles so that wasn't an option for us. We used a sheet and added a blanket on colder days/nights. Tucked it in at the sides and always put it under her arms so, also ensuring that she was placed feet to the foot of her bed (all advise from FSID and other SIDS charaties). Once she was 5 months she started moving a lot more and the problem was that she often uncovered her self so we bought a baby sleeping bag, this helps a lot and she sleeps well and there isn't a risk of her covering herself with the blankets.

you dont need to keep them at steady 98 degrees. They can regulate their bodytemps at birth. ( as long as its not a preemie) .Just put on a long sleeved bodysuit or you can use one of those sleepsacks. Its like a sleepingbag excpet the head and arms come out of it and the rest of the body is zipped into the bag.. keep a little hat on them at first few nights or weeks and they will be fine in regular room temps ( 70+ degrees)

edit about the swaddling, not every baby likes to be swaddled. My first one hated it and would kick and wiggle until he got out and then he was happy laying in an X-position in his crib. my second liked it for about a week and then he was over it, my third was also about a week or two and that was it.. If they keep wiggling and kicking it off then just give up on the swaddling. Not all babies like it. they are happy to be 'free' after being in womb for so long :)

You can swaddle a newborn. they don't move much so as long as the blanket is away from their face it usually stays that way. For bigger more wiggly babies you can make a sleep sack that only comes up to their chest. It's like a sleeping bag made from baby blankets so it sort of looks like a pillow case. Once they can wiggle out of that, blanket sleepers only.

Swaddling

swaddle rs are great you purchase them at any baby store. Or you can swaddle them yourself using receiving blankets. Babies like to be snuggled up and bundled tightly so the swaddle methods works great! both my boys couldn't sleep as newborns unless they were swaddled.

they also make fleece zip up nightgowns (for boys and girls) they are like a wearable blanket I own zillions of these I had winter babies and live where is very very cold! Carters I think is the most popular brand check out their website if not they sell them at most department stores.

You use a sleeper (pajamas that cover the whole body) and when you have the baby, the hospital should teach you how to swaddle a baby (so that you can wrap them in a blanket without it getting in their face).

Also, please use baby hats and mittens when you go out.

An extra layer of clothing like footed pajamas or a sleep sack, and/or swaddling if still young.

I used a swaddle but now that my daughter can roll over I bought fleece jammies and on cold nights she wears them. she has had no issues with them.

swaddling is very important and try putting a baby hat and booties on them