Pregnancy

The first trimester consists of the first 14 weeks of the 40-week pregnancy. During this time, a woman may experience various emotions due to the hormonal changes in her body, and she may experience “morning sickness” at any time during the day or night.

During the first trimester, nearly all of the fetus’ internal organs form. The fetus is approximately the size of a fist and can even begin to move a little.

During the second trimester, weeks 15 through 27, a woman may experience symptoms of heartburn and indigestion. The baby’s growth in the abdominal area becomes noticeable, and stretch marks may develop as the skin of the abdomen expands. The developing fetus grows very rapidly during the second trimester, and the fetus’ arms and legs become well developed and strong. The expectant mother may begin to feel the baby moving inside. Although the fetus is almost fully formed, the lungs need to develop further while the fetus puts on more fat and weight.

During the third trimester, weeks 28 through 40, the baby continues to grow and the lungs develop further. It can be difficult for a woman at this stage to find a comfortable position either awake or asleep.

The baby’s growing body within the uterus pushes the abdominal organs up under the diaphragm and compresses the bladder and colon. Near the end of the 40-week cycle, the baby drops down into the pelvic cavity, which is nature’s way of saying, “It’s time to give birth”.

Review Date: 2/3/2025

Reviewed By: Peter J. Chen, MD, FACOG, Associate Professor of OBGYN at Cooper Medical School at Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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06/01/2025

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