How big is our baby at 17 weeks pregnant? About five inches long and more than three and a half ounces — the size of your open hand. Body fat (baby's, that is) is beginning to form and will continue to accumulate through the end of pregnancy. By the time our baby is born, body fat will make up about two-thirds of his or her weight. Our baby is almost certainly listening up by now. In fact, loud noises — the dog barking, the doorbell ringing — will actually startle the baby (and also get him or her used to such noises; for instance, fetuses who regularly hear a dog barking will become babies who sleep right through a dog's outbursts). Your baby's eyes (which have fortunately finished their migration to the front of his or her head) are making small side-to-side movements and can even perceive some light, though the eyelids are still sealed. And since practice makes perfect, our baby is sharpening his or her sucking and swallowing skills in preparation for that first (and second…and third) suckle for feeding. In fact, most of the survival reflexes that our baby will have at birth are being perfected in utero right now. It's amazing at how much the baby has already developed. I'll keep you posted!!