Mam: Pregnant 31 weeks (Baby 29 weeks)
At 31 weeks pregnant, your uterus can now be felt four inches above your belly button
You might notice a milky liquid leaking from your breasts at this stage – this is called colostrum, the fluid that precedes breast milk, and just means that the milk production is good to go, ready for baby!
Movin' on up at 31 weeks pregnant, your uterus can now be felt four inches above your belly button. This means that your uterus is pushing all the internal organs that used to be there somewhere else, crowding your lungs and making it more difficult for them to expand fully. The result: Your body is spare on air and will be until your baby drops near the end of pregnancy in preparation for birth. While this shortness of breath may feel very uncomfortable to you, your baby is as happy as a clam because he’s getting his oxygen from the placenta.
That out-of-breath feeling may get better toward the end of your pregnancy, when your baby (and its uterine home) drops down into your pelvis in preparation for delivery. Until then, be sure to stand as straight as you can (given the weight you're carrying around) and sleep propped up or on your side so that your lungs have more space to... well, breathe. 
What to Expect discusses week 31 of pregnancyfind out more
Langmans Medical Embryology, Ninth Edition, TW Sadler, 2003find out more