Is My Baby Bump Normal at 16 Weeks? - Dr. Rappaport Answers

Question
Hello Dr. Rappaport,
I am 24 years old and have two children ages 2+3. I am currently pregnant with my 3rd child. The date of my last period was around June 17, which makes me about 16 weeks now. My question is that to me, my stomach looks increadably big to be 4 months along. I had an ultrasound at 6 weeks because I was cramping and have 1 miscarriage in my history. The ultrasound showed the baby's heart beat was abnormally slow.
I know I am not having twins because they would have seen it in the ultrasound. My doctor has scheduled me for an ultrsound next week. To me it seems a little too soon to have one, my previous pregnancies I believe I was 20 weeks along. Should I be concerned by my doctor wanting to do one so soon? Is there anything to be worried about being so big at this stage. I think I look at least 6 months pregnant. I hope I didn't confuse you too much with my question. Thank you for your response.
Shana

Answer
At 16 weeks gestation, if you lie on your back, you should feel the fundus of your uterus 4 fingers (cm) below your belly button. At 20 weeks, it will be at the level of the belly button. A sonogram will be accurate anytime after 14 weeks gestation. It will reassure you of a normal baby. I can't tell what the slow heartbeat meant. It should be between 120-160 beats per minute during pregnancy. Good Luck.