It sounds like you are experiencing sleep apnea - a condition where breathing stops during sleep. You mustn't panic, your body is 'programmed' to re-start your breathing after a few seconds, and there is no danger at all of your stopping breathing during birth - your body's survival instinct for yourself and baby will prevent that, and you will have the medical support you need to oversee everything and keep you safe. If it is bothering you, have a word with your GP - it may be a temporary condition caused by pregnancy, but your doctor will advise and set your mind at rest.