The Fetal Period of Pregnancy: Definition & Development

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  • 0:01 The Fetal Stage
  • 0:31 What Happens During…
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Lesson Transcript
Instructor: John Williams
The fetal stage of pregnancy is a critical developmental phase for an unborn child. Many key changes take place to prepare the child for independent living outside of the womb. This article discusses the critical time periods within the fetal stage of development.

The Fetal Stage of Pregnancy

Pregnancy is a period of time in which a developing child resides within a mother. During this time, the child will begin to physiologically develop the tissues, organs, and other structures needed for survival. Pregnancy is described in many different ways: by months, by weeks, and by structural stages. One of the most critical stages of development during pregnancy is the fetal stage. Let's discuss the fetal stage, and what developments take place at this point in pregnancy.

What Happens During the Fetal Stage?

The fetal stage officially begins after the tenth week of pregnancy. Prior to this, the developing child is considered an embryo. Before the tenth week is reached, many physiological developments have already happened. By this point, the embryo:

  • Has started the process of developing heart and nervous tissue
  • Has started developing a gastrointestinal tract
  • Has distinguishable limbs

The embryo also has other key features that will continue to develop in the fetal stage. During the fetal stage, many of the body systems will begin to mature. By week 14, the genitals will be easy to differentiate. While doctors usually wait until at least the 18th week of pregnancy to reveal the gender, accurate identification can be done as early as 13 weeks. Additionally, around this time, the facial features become more defined.

Between weeks 13-16, the fetus begins to move, which means the muscles are developing. The skeleton of the fetus is, at this point, primarily cartilage, or soft connective tissue, but may also contain some hardened bone. This is also the period where the liver and pancreas, both accessory digestive organs, will begin secreting enzymes and hormones within the fetus.

By week 19, the heartbeat of the fetus can be detected clearly with a stethoscope. From there, the lungs and alveoli, or air sacs, will develop around week 23 as the respiratory system continues to form. Another development that starts around this time is the integration of nervous system control over the body functions.

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