I think they're referring to a egg crate mattress cover. You can get one at any department store for about 20. Goes under the sheet but on top of the mattress to help with weight distribution on the hips. The pad is usually white or yellow and literally resembles a huge egg carton.
I use a pregnancy pillow and an egg crate mattress cover. I got the pregnancy pillow first and that helped a lot, but then about a month later I started to get back pain again. The egg crate has helped a lot.
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I got a memory foam mattress topper instead. Between it and the Snoogle, I am totally set! Kohls had a great sale on them for Black Friday weekend. Might be worth checking their site if you think you need one.
Re: Egg Crate for Mattress?
www.BrandtTriplets.com.