Shushing — mimic the whooshing sounds of the womb by either making the sound with your mouth or by playing white noise (myorganicformula.com)
Sleep Sheep features a heartbeat setting that mimics the comforting sounds of the womb in addition to three white noise options. (blog.guguguru.com)
The soft whooshing and whirring sounds of the womb are combined with mellow female vocal harmonies and breathing to produce a gentle and pleasant sound. (lllmarivt.org)