Prenatal Development

When does my baby’s heart start beating?

When can I feel my baby moving for the first time? When is the earliest my baby is able to survive outside of the womb?

To answer these questions and any others you might have, let’s go through the 40 weeks of your baby’s development and see what happens along the way.

Mom Getting Ultrasound

Fetal development is broken down into 3 trimesters.

  • The first trimester lasts from week 1 through 11 weeks
  • The second trimester lasts from 12 weeks through 24 weeks
  • The third trimester lasts from 25 weeks through the end of your pregnancy which is basically 38-40 weeks.

A lot of basic growth occurs during the first trimester of pregnancy. In fact, the first few weeks see the beginning of the basic development of brain, spinal cord, heart, and gastrointestinal tract. On day 22 the baby's heart begins beating.

In week 4 the formation of the lungs, jaw, nose, and palate has begun and the brain is continuing to form into all of its complex parts. By week 6 everything that is present in an adult human is now present in the small baby. Plus the bones are beginning to form and the muscles can contract.

By the end of the first trimester, the fetus has grown to about 3 inches in length and weighs about an ounce.

In the second trimester the baby starts moving around a lot more and usually by week 16 the mother can feel movement. Fingerprints have now developed on the tiny fingers of the baby and the liver and pancreas now produce fluid secretions.

By week 18 the eyebrows and eyelashes have now grown in, and nails have begun to grow on the fingers and toes. Also, a baby’s hearbeat can now be detected by a stethoscope. Between weeks 19 and 21 the liver, pancreas, and the eyes are developing completely.

At the end of the second trimester the brain will be developing rapidly and the baby has developed sleeping and waking cycles which can be detected by mom. The baby is now able to live outside of the womb with medical help if delivered early and should weigh about 2 1/2 pounds and be about 14″ long.

During the third trimester the baby really starts filling out and storing body fat. Some breathing movements are occurring even though the lungs are not fully developed. By week 30 the baby’s bones are fully developed but still soft and flexible.

During weeks 31-34 the baby’s head starts to descend into the mother's pelvis getting ready for birth. As the baby continues to grow, the mother may start to feel less movement as the baby starts to run out of room.

At 38 weeks the baby is now considered to be full term and can be born at any time. The baby’s organs are now fully developed and the lungs continue to develop until the day of delivery.

At birth a baby is generally between 6 3/4 and 10 pounds as well as between 18-21″ long.

For more information about fetal development, you can go to the American Pregnancy Association, or come into Choices to learn more.

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