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Phone: 202-223-8073
Fax: 571-312-0544

2776 S. Arlington Mill Dr.
#803
Arlington, VA 22206

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Charlotte Lozier Institute

Phone: 202-223-8073
Fax: 571-312-0544

2776 S. Arlington Mill Dr.
#803
Arlington, VA 22206

The
Voyage of Life
Preparing for Pregnancy
Week 0 to 1
Week 1 to 2
Week 2 to 3
Week 3 to 4
Week 4 to 5
Week 5 to 6
Week 6 to 7
Week 7 to 8
Week 8 to 9
Week 9 to 10
Week 10 to 11
Week 11 to 12
Weeks 13 & 14
Weeks 15 & 16
Weeks 17 & 18
Weeks 19 & 20
Month 6 to 7
Month 7 to 8
Month 8 to 9
Month 9 to Birth

Week 3 to 4

First heartbeat and neural tube development

Human Prenatal Age
  • PCW 4
    i
    Post-Conception Week
  • Days 21-27
  • Gestational Week 6
Highlights

  • The heart starts beating.1

  • By the end of the week, the neural tube has closed and the brain has divided into three primary sections: the forebrain, midbrain, and hindbrain.2 

  • Sensory areas such as the eyes, ears, and nose start forming.3 

The changes in the embryo between the beginning and end of the fourth week are dramatic. Like rumpling a flattened blanket, flattened embryonic tissue begins folding, forming a tube that will become the brain and spinal cord. More folding forms the chest and abdominal cavities. Clusters of cells start growing in just the right locations to form the upper and lower limb buds. These buds will become the arms and legs.4

Furthermore, after only 22 days in the womb, the embryo has a heartbeat!5  At this point, a woman will have likely been aware of her pregnancy for only about a week.

By 22 days after fertilization, the heart starts beating.6 The heart beats about 54 million times between conception and birth.7 

How many times has your heart beat?
Calculate It Now

Doctors use a variety of methods to listen to the fetal heartbeat. At first, the sound and motion from the heart is barely detectable. Doctors use ultrasound technology to see the motion of the heart in early pregnancy. Starting 10 weeks after conception, many doctors will use a Doppler fetal monitor to check the fetus’s heart rate.8  A fetal Doppler monitor uses the motion of the blood within the heart to make an audible signal and measure the heart rate.

Although this video is from an older embryo, the heart starts beating 22 days after conception.
How does the brain start to form?

Just 22 days after fertilization, the neural tube starts to close. Folds of neural tissue fuse together, starting in the neck area, continuing towards the head and rump. The neural tube becomes the brain and spinal cord. The brain finishes fusing by the 25th day, and the bottom of the spinal cord finishes fusing by the 28th day. The brain grows in three sections: the forebrain, midbrain, and hindbrain.9  The forebrain is responsible for sensing, decision making, and forming memories; the midbrain is responsible for localizing sounds, moving, and tracking objects; and the hindbrain is responsible for vital body functions. Later in development, pain processing occurs in all three sections of the brain.10

Doctors can count the number of small bumps along an embryo’s back to accurately estimate her age.

Doctors can count the number of small bumps along an embryo’s back to accurately estimate her age. The bumps are called somites and first appear 20 days after conception. The number of somites present in the embryo in the following week can be used to give an exact age. For example, at 22 days the embryo has 7 distinct somites, while by day 28 there are about 25 somites.  As somites mature, they form bones and muscles.11

Dive Deeper
Highlights of the Early Heart
The embryonic heart starts beating 22 days after conception...
Read More
Embryonic Heartbeat Fact Sheet
There is a functional, beating heart in every human being by 6 weeks of gestation.
Read More
Back to The Voyage of Life
Sources
  1. Tan C, M, J, Lewandowski A, J: The Transitional Heart: From Early Embryonic and Fetal Development to Neonatal Life. Fetal Diagn Ther 2020;47:373-386. doi: 10.1159/000501906
  2. Sadler, Thomas W. Medical Embyrology. 14th ed., 2019.
  3. Moore, Keith L, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  4. Sadler, Thomas W. Medical Embyrology. 14th ed., 2019.
  5. Tan C, M, J, Lewandowski A, J: The Transitional Heart: From Early Embryonic and Fetal Development to Neonatal Life. Fetal Diagn Ther 2020;47:373-386. doi: 10.1159/000501906; Asp, Michaela, Stefania Giacomello, Ludvig Larsson, Chenglin Wu, Daniel Fürth, Xiaoyan Qian, Eva Wärdell et al. 'A spatiotemporal organ-wide gene expression and cell atlas of the developing human heart.' Cell 179, no. 7 (2019): 1647-1660. https://doi.org/10.1016/j.cell.2019.11.025.
  6. Tan C, M, J, Lewandowski A, J: The Transitional Heart: From Early Embryonic and Fetal Development to Neonatal Life. Fetal Diagn Ther 2020;47:373-386. doi: 10.1159/000501906; Asp, Michaela, Stefania Giacomello, Ludvig Larsson, Chenglin Wu, Daniel Fürth, Xiaoyan Qian, Eva Wärdell et al. 'A spatiotemporal organ-wide gene expression and cell atlas of the developing human heart.' Cell 179, no. 7 (2019): 1647-1660. https://doi.org/10.1016/j.cell.2019.11.025.
  7. EHD: Appendix. “Appendix | Prenatal Overview.” Accessed April 3, 2020. https://www.ehd.org/dev_article_appendix.php
  8. Moore, Keith L, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  9. Sadler, Thomas W. Medical Embyrology. 14th ed., 2019.
  10. Slobodan Sekulic et al., “Appearance of Fetal Pain Could Be Associated with Maturation of the Mesodiencephalic Structures,” Journal of Pain Research 9 (2016): 1031, https://doi.org/10.2147/JPR.S117959.
  11. Sadler, Thomas W. Medical Embyrology. 14th ed., 2019.
See Full Bibliography

All images and illustrations on The Voyage of Life were reviewed by credentialed scientists for accuracy.

Medical art animation was used to provide a schematic representation of fetal development, with some features, including timing, not to scale. The animation was chosen as an ethically uncompromised guide to fetal development. There are many real human images at each developmental age showing the most accurate fetal forms throughout development. A concerted effort was made to use images and material in which the human embryo or fetus did not undergo any known harm.

Page last updated on March 11, 2023