Your baby can benefit from some extra days in the uterus, but he's full-term! He is likely to weigh 6 pounds, and he's probably close to 20 inches long. But even your practitioner can't tell how big your baby will be at birth since some of those 30 pounds or so that you've gained come from increased amniotic fluid, breast size, and placental growth.
In fact, your body weight probably won't tip the scale much higher, but your baby will continue adding ounces. During the few weeks (or days) left before you deliver, your baby may add up to 14 grams of fat each day. At the same time, some of your amniotic fluid is starting to be reabsorbed by your tissues, slightly decreasing the fluid around your baby. This may make it feel as though your baby is moving less, but he's actually just as active as before within his increasingly cramped quarters. As your uterus stretches, more light will permeate your baby's space, and he will move his eyes toward it.
Because placental hormones are now stimulating your breasts to produce milk, those same hormones will cause your baby's mammary glands to swell too. They will shrink back down to size after birth.
What's more, during these last few weeks (or days!) before birth, your body and your baby's body will start preparing for the rigors of labor. The umbilical cord begins passing antibodies to your baby in preparation for delivery. By stockpiling antibodies, your baby will be better prepared for the disease and germs he'll encounter outside the womb.
Added weight will also help your baby survive, and thrive, once he's born. His body needs plenty of insulation now that he'll no longer be able to rely on the warm environment inside the amniotic sac to keep her cozy. His body will need to start doing that job all on its own after delivery — of course, you'll also be there to hold him close and keep him snug.
Your baby's senses are also getting more time to hone his burgeoning skills. He can hear and recognize your voice. Once he's born you'll be able to see him turn his head in your direction when he hears you speak. He knows her mom! Along with his hearing, his eyesight is improving each day. His fingers are also becoming more coordinated. He can grasp her face or toes. And after birth he'll be able to grab onto your finger.
On a side note, sonographers rarely see an unborn baby's reactions to light sources in utero. Since ultrasounds are usually performed in darkly lit rooms, your baby doesn't have any light to react to!
Mucus plug: The thick, phlegmlike substance that forms a ?plug? in the cervical opening. This ?cork? keeps germs from entering the uterus and harming your unborn baby. In the days or weeks before delivery you might notice a mucuslike discharge, indicating that you are losing your mucus plug. The loss does not mean that delivery is imminent, but that your body is readying for birth. Some expectant mothers never notice the loss of their mucus plug.
Images courtesy of the American Institute of Ultrasound in Medicine (AIUM.org).