How does my baby develop in the third trimester?

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Lots of important things happen to your baby in the last few weeks of pregnancy. For example, your baby's brain and lungs are still developing. Being pregnant for at least 39 weeks gives your baby’s body the time it needs to grow and develop. Learn more at: marchofdimes.org/week-by-week
The third trimester is the period of greatest growth for your baby, who is starting to gain about one-half pound every week. Her organs are continuing to mature. She sucks her thumb, looks around her snug little world and has definite periods of activity and rest. By 36 weeks or so, she will start settling into her birth position, which is head-down for most births.

During the third trimester the fetus is getting ready for birth and extrauterine life.

By the beginning of the third trimester all the major body organs are present but not yet functional for existence outside the uterus. For example the lungs are present and some rhythmic breathing movement are occurring, but the pulmonary vascular structure and surfactant production necessary for breathing air are not yet mature. Therefore during the third trimester the functional abilities of the organ systems are readied for life outside the uterus.

In the third trimester, the fetus’ appearance changes, taking on characteristics of a newborn. The fetus’ transparent, red, wrinkled skin smooths out  and gains opacity as the fetus gains weight and develops a layer of underlying or subcutaneous fat. Also the lanugo or soft hair that has covered the fetus’ body begins to fall off. Finally, toe nails become visible, finger nails grow and small breast buds appear.

During the third trimester the fetus is growing. At the beginning of the third trimester the fetus is about 12-14 inches in length and weights a little over 2 pounds. By the end of the third trimester the fetus weight between 7-10 pounds and is approximately 19-21 inches in length. The fetus’ arms and legs become chubby and the mother may notice a change in fetal activity as the fetus is now filling the uterus. While fetal “flips” are no long possible, there will still be a lot of stretches, wiggles and rolls. A lack or decrease in fetal movement is a reason to contact the health care provider. During this time the fetus has developed fat stores as well as its own stores of calcium, iron, phosphorus, glucose and brown fat.

Finally during the third trimester the fetus prepare for the journey through the birth canal. The majority of  fetuses assume a head down position  and settle into the pelvic bone awaiting the onset of labor and their journey to the outside world.

Continue Learning about 3rd Trimester Of Pregnancy

3rd Trimester Of Pregnancy

The final few weeks of your pregnancy will put the most strain on your body. Extra weight will cause back pain, breasts will be at their largest, and you may suffer from mild contractions. Swelling may also cause your ankles, face...

, and hands to become puffier than usual. Fatigue will usually set in after the 2nd trimester due to extra weight, broken sleep patterns, and stress from upcoming delivery. The baby is now pressing down on your bladder so urination is more frequent than ever. If you notice discharges are heavy or blood-colored, visit you doctor. It may be a sign that you lost your mucus plug and are dilating for labor.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.