Sometimes younger women or women with certain health problems can have babies that are Small for Gestational Age, which just means that they developed at a slower rate for some reason (sometimes age is a factor but you're not THAT young). I'm surprised your doctor hasn't considered that your baby may simply be smaller than most babies...4 wks isn't a huge difference once you're past 36 wks so at any point if you deliver your baby SHOULD be fine and full-term. You may simply have miscalculated because you may ovulate later in your cycle than most women, so you may not have conceived until later in your cycle so you may be off by a week or two that way. Just try to relax and wait it out...I went through the same anxiousness and my baby was right on target; went into labor ON her due date. Just stay calm and see what happens....most likely you'll deliver in early late Oct/early Nov because most first pregnancies don't deliver right at 40 wks. I have a friend who delivered her first baby at 41 wks, second baby at 41 wks, and third baby at 42 wks, so you never know! They might be off, you might be off...but that baby'll come out when she's ready. Good luck, and congrats on your little girl! (i just want to add...if you are absolutely sure that you calculated right, stick to your guns. my doctors kept moving around my due date and finally i just told them "no, my due date is Sept 22 and that's that." i'll be darned if i didn't go into labor on the 22nd ). Also....what was the height of your fundus (top of your uterus?) that's usually a pretty good indicator of fetal age. the cramping and spotting may be Braxton Hicks contractions and the mucus plug getting ready to shed.