I've had 2 healthy deliveries in the past with no complications. This is my 3rd baby and according to my LMP which was 12/29/2015 I should be 9 weeks and 1 day pregnant but when I went in for my first OB appointment they gave me an ultrasound and the baby is only measuring 7 weeks and 1 day. They listened to the heartbeat and said that it was a healthy beat, and said that I should not be worried but I can't help but to worry because the baby was so small. My question is should I be worried? How did this happen? Will my baby be alright?