Your fetus is about three inches long and the size of a peach at 13 weeks pregnant.But don't compare your fetus with the fetus next door. Starting aboutnow, babies begin growing at different paces, some faster than others,some more slowly, though they all follow the same developmental path.Growing at a universally breakneck speed now is your baby's body as ittries to catch up to the head in terms of size. Though your baby's headis about half the size of its body now, by the time your baby is readyto make his or her entrance into the world, the head will be onlyone-fourth as large as the body.
 
Your baby's intestines arealso in for some big changes right now. Up till this point, they'vebeen growing in a cavity inside the umbilical cord; but now they'removing to their permanent (and more conveniently located) address, inyour baby's abdomen.  And to serve your growing baby's needs, theplacenta is also growing.  It weighs about an ounce now and will weighone to two pounds at birth (something else you'll soon be able to blameyour weight gain on!).

Alsodeveloping this week: your baby's vocal chords. Because sound can'ttravel through your uterus (your baby's current habitat), you won't beable to hear any sounds or cries just yet, but oh boy (or girl) — thosevocal chords will get a good workout once that baby is born.