Mam: Pregnant 18 weeks (Baby 17 weeks)
Shopping for baby clothes! Your uterus has moved up just below your navel, and is about the size of a football.
Your uterus has moved up just below your navel, and is about the size of a football.
Your cardiovascular system is undergoing dramatic changes, and during this trimester your blood pressure will probably be lower than usual. Don't spring up too fast from a lying or sitting position or you might feel a little dizzy.
From now on, when you do lie down, it's best to lie on your side — or at least partly tilted to one side. (When you lie flat on your back, your uterus can compress a major vein, leading to decreased blood return to your heart.) Try placing a pillow behind you or under your hip or upper leg for comfort. 
BabyCentre discusses week 18 of pregnancyfind out more
Langmans Medical Embryology, Ninth Edition, TW Sadler, 2003find out more