The third trimester is traditionally a time when the new mother begins to gather clothes and supplies and prepare a room for the forthcoming infant. She has passed through morning sickness, and through the relatively easy second trimester. The third trimester is characterized by rapid growth of the mother and the baby. This is a vital time for creating a full-term baby with a healthy future.
Growth
Most obvious for the mother is the growth of the belly during the third trimester. The baby will gain a lot of weight in this trimester. Starting at only 2 pounds, by the birth the baby will be 7 or 8 pounds. Gaining weight makes the fetus look less wrinkled. The eyes open, and around the 33rd week, the baby can see light.
Bones and Muscles
The bones are all there and in the right shape, but they are still soft until the last days. The little body has started storing minerals: calcium, iron and phosphorus. The baby has been moving from almost the beginning, but now the baby can no longer spin around and kick. The movements might even feel painful to the mother as the baby's muscles strengthen and the baby stretches. Remember to keep track of the movements and report to the doctor if they discontinue. The observant mother will start to detect a routine: sleeping and waking cycles.
Features
Fingernails, toenails and hair also appear during this trimester. Eyelashes grow around the eyes. The hair-like lanugo that was all over the body falls off and the hair on the head grows--if the baby is destined to have hair on his head; some are born bald. In an ultrasound, you might see the baby sucking his thumb or grasping the umbilical cord with his hand.
Lungs
One of the biggest limitations with premature births are the lungs. The lungs need almost the entire 40 weeks of pregnancy to develop. The baby starts to practice breathing around the 32nd week, but the lungs may not be ready for the real thing. If it looks like a premature birth is imminent or needed, drugs will be administered to help the baby's lungs develop.
Organs Getting to Work
The heart started beating early on, but in the third trimester, the liver and kidneys also start to work. The baby will excrete into the amniotic fluid. The baby will also drink some of the amniotic fluid.
Full Term but Still Developing
At 37 weeks, babies are considered full term. They can likely live safely outside the mother. Babies are not delivered at this time because there is still more important development going on. The baby’s grip is getting stronger. Her genitalia are becoming more developed, and the brain and nervous system are becoming more under control. These last weeks give the baby some more fat and antibodies to help her deal with the world outside.
