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What are the Different Prenatal Stages?

By Rolando Braza
Updated May 17, 2024
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There are three basic prenatal stages: the conception stage, followed by the embryonic stage, and finally the fetal development stage. It is during these stages that the baby's different organs and body systems are developed. Prenatal development usually takes around 40 weeks — about nine months — to complete. In each of the prenatal stages, processes and changes happen in the body of both the baby and the mother.

The conception stage serves as the preparation stage for the pregnancy and lasts for about two weeks. During this stage, a thick tissue rich in blood typically grows in the womb of a pregnant woman. It is also at this stage that the sperm fertilizes a woman's egg in one of her two fallopian tubes. The fertilized egg, which is known as a zygote, will then travel to the uterus.

The arrival of the egg in the uterus signals the start of the embryonic stage — the second of the three prenatal stages that will progress until about the 11th week of the pregnancy. At this stage, cell division usually transpires at approximately the fourth week to produce the embryo and the placenta, the organ that will connect the developing embryo to the mother through her uterine wall. At around the sixth week, the heart normally starts to beat, and the embryo's arms and legs will likely start to develop. When the pregnancy reaches its eighth week, the intestines as well as the teeth will usually begin to develop. Generally, when the 11th week is reached, nearly all of the body parts are usually in place, including the different joints of the body, the irises of the eyes, and the central nervous system.

The last of the three prenatal stages is the fetal stage. After about the 16th week, the embryo is referred to as a fetus, and normally starts to develop genitals, vocal cords, and liver and kidneys that are already functional. He or she starts to have hair and nails, and his or her bones become hard. The growth of the fetus then typically speeds up to about the 20th week, as the heart of the fetus starts to pump larger amounts of blood and fat starts to build up beneath the skin.

Around the 21st to the 24th week, the lungs of the fetus ordinarily start to develop and prepare to take in air. The eyelids and eyebrows become fully formed. The retina begins to form, and the fetus may be able to open and close his or her eyes at this time. By the 39th or 40th week, the fetus is typically ready to emerge from the womb and become a neonate with almost all his or her main organs fully developed.

Pregnant woman should have regular check-ups by a medical professional to ensure the good health of both herself and her child. Regular monitoring allows a health care professional to detect any complications that may arise during prenatal development and address urgent issues on the pregnancy. It can enhance the likelihood of a safe delivery of the baby.

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