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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
Weeks 0 and 1
Week 2
Week 3
Week 4
Week 5
Week 6
Week 7
Week 8
Week 9
Week 10
Week 11
Week 12
Week 13
Week 14
Weeks 15 & 16
Weeks 17 & 18
Weeks 19 & 20
Weeks 21 & 22
Month 6
Month 7
Month 8
Month 9
Birth

Week 5

First heartbeat and neural tube development

Human Prenatal Age
  • Post-conception week 3
  • Days of life 21-27
  • Gestational Week 5
Highlights

  • The heart starts beating 22 days after conception.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 and ears start forming.3

The changes in the unborn baby between the beginning and end of week 5 are dramatic. Like rumpling a flattened blanket, flattened embryonic tissue begins folding, forming a neural tube that will become the brain and spinal cord. More folding creates the chest and abdominal cavities.4

When does the heart start beating?

Only 22 days after conception or 5 weeks and 1 day gestation, the unborn baby’s heart starts beating.5 6 This is sometimes called the sixth week of pregnancy because 0 weeks and 1 to 6 days is known as the first week of pregnancy, so 5 weeks and 1 to 6 days is also known as the sixth week of pregnancy.

At 23 days after conception , the heart beats between 947 to 98 times per minute, and subsequently begins to rise.8 By the end of week 5, the heartbeat has increased to an average of 108 beats per minute.9 Once the heart starts beating rhythmically, it does not stop until the person dies. The heart moves oxygen-carrying blood throughout the developing embryo so that he can continue to grow. Without a heartbeat consistently circulating blood, new tissues would not have enough oxygen to survive.10

A heartbeat is sometimes visible in week 5, around the same time many women discover they are pregnant.11 Although pregnancy can be confirmed by a trained medical professional using ultrasound to detect the early heartbeat as early as 5 weeks and a few days gestation, it is more consistently detected at 6 weeks.12

This composite image rendered from light-guided endoscopy recordings shows an embryo alive in the womb at 3 weeks following [tooltip anchor="fertilization"]Sperm-egg fusion[/tooltip] (or 5 weeks gestation). The groove in the embryo's back becomes the brain and spinal cord. (Image Credit: <a href="https://erf.science/#high-resolution">Education Resource Fund</a>)
This composite image rendered from light-guided endoscopy recordings shows an embryo alive in the womb at 3 weeks following fertilization (or 5 weeks gestation). The groove in the embryo's back becomes the brain and spinal cord. (Image Credit: Education Resource Fund)
With the first heartbeats, the average rate is 94 to 98 beats per minute.13 14

Understanding the timing of a baby’s first heartbeat can be confusing because there are two different ways to report the time of pregnancy. Embryonic ages are measured from conception, the beginning of a new human life. But most medical professionals and mothers use gestational age based on the mother’s last menstrual period. The gestational age of a baby is typically two weeks greater than embryonic age.  Therefore, it is scientifically accurate to say that the heart starts beating at 5 weeks and one day gestation or 3 weeks and one day after conception.  Both facts are correct; they are just two different ways of saying the same thing. This website uses gestational age for clarity.

Only 22 days after conception or 5 weeks and 1 day gestation, the unborn baby's heart starts beating. 15
How many times has your heart beat?
Calculate It Now
The heart tube as it looks when the heart first starts beating. (Image credit: Science Source)
The heart tube as it looks when the heart first starts beating. (Image credit: Science Source)
What does the early heart look like?

Around five weeks, the baby’s heart is just beginning to take shape. It starts as a simple tube, growing quickly.  This tiny heart tube forms from special tissue guided by genetic instructions and chemical signals from the surrounding body structures. Muscle contractions cause a pumping motion in the heart tube, that becomes rhythmic by day 22.16 Interestingly, the motion and pressure of blood moving through the heart tube causes parts of the tube to become more like the heart’s final shape, since heart cells change their shape and size in response to mechanical stress.17

How does the unborn baby make blood vessels?

Around 5 weeks, the baby’s body starts making blood vessels. Blood vessels form in two main ways throughout development:

  1. Vasculogenesis – Special cells come together in long lines and hollow out to form new blood vessels. The major blood vessels, like the aorta and major veins, form via vasculogenesis.18
  2. Angiogenesis – Once the first vessels are in place, new vessels sprout and grow out from them, like branches growing from a tree. Most blood vessels and capillaries in the body form via angiogenesis.19 20
How does the brain start to form?

Just 22 days after conception or 5 weeks and 1 day gestation, 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.21 The brain finishes fusing 25 days after conception, and the bottom of the spinal cord finishes fusing 28 days after conception.22 The brain grows in three sections: the forebrain, midbrain, and hindbrain.23 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.24 Even before the top end of the neural tube has fused together, the eyes start forming as little bubbles of neural tissue on either side of the forebrain, 22 days after conception.25

Eventually, the brain will be divided into hemispheres — the left and right halves of the brain. By 5 weeks gestation, the primitive versions of these hemispheres have developed.26 The primitive thalamus is also first identified during week 5.27 The thalamus will serve important roles in pain perception, and sensory and motor integration.

At the beginning of week 5, the gestational sac is usually visible via ultrasound in viable pregnancies. The double decidual sac sign shown in this picture indicates that the embryo has implanted in the correct place, in the uterus. (Image Credit: <a href="https://synapse.koreamed.org/articles/1516091459">Synapse</a>)
At the beginning of week 5, the gestational sac is usually visible via ultrasound in viable pregnancies. The double decidual sac sign shown in this picture indicates that the embryo has implanted in the correct place, in the uterus. (Image Credit: Synapse)
Future eggs and sperm

Just weeks after conception, the baby’s body starts preparing for his or her future children! Primordial germ cells are large specialized cells that become sperm or egg-producing cells, depending on whether the baby is a boy or a girl. By about 24 days after conception , they can be found near the base of the umbilical cord. From there, they migrate through the developing body to the testes or ovaries, where they will one day make sperm or eggs, laying the groundwork for the next generation.28

What are somites?

Somites are small, paired blocks of tissue that form along an embryo’s back and lay out the body’s basic structure. They first appear about 20 days after conception and can be counted to estimate the unborn baby’s age. For example, there are about 7 somites at 22 days and around 25 by day 28.29 As somites mature, they give rise to bone, muscle, cartilage, nerves, and the skin of the back.30

Continued development at 5 weeks of pregnancy

The respiratory system begins forming around 22 days after conception.31 The lungs develop from two small lung buds that grow in front of the gut tube.32

Dive Deeper
Highlights of the Early Heart
The embryonic heart starts beating 22 days after conception...
Read More
Blood formation
Blood starts forming before the first heartbeat, about 17 days after conception...
Read More
Back to The Voyage of Life
Sources
  1. ^ Tan, C. M. J., & Lewandowski, A. J. (2020). The transitional heart: from early embryonic and fetal development to neonatal life. Fetal diagnosis and therapy, 47(5), 373-386. https://doi.org/10.1159/000501906 Note that this paper uses the term gestation to mean post-conception.
  2. ^ Sadler, T.W. (2024) Langman's Medical Embryology. 15th ed. p. 320, Fig 18.4.
  3. ^ Torchia, M.G., and Persaud, T.V.N (2025). The Developing Human, Clinically Oriented Embryology. Elsevier. 12th ed. p.359, Fig 17.3D
  4. ^ Sadler, T.W. (2024) Langman’s Medical Embryology. Wolters Kluwer. 15th ed.
  5. ^ Britten, S., Soenksen, D. M., Bustillo, M., & Coulam, C. B. (1994). Pregnancy: Very early (24–56 days from last menstrual period) embryonic heart rate in normal pregnancies. Human Reproduction, 9(12), 2424-2426. https://doi.org/10.1093/oxfordjournals.humrep.a138462 Note that this original research measured days since LMP, so we subtracted 14 from the days listed to get the gestational age.
  6. ^ Tan, C. M. J., & Lewandowski, A. J. (2020). The transitional heart: from early embryonic and fetal development to neonatal life. Fetal diagnosis and therapy, 47(5), 373-386. https://doi.org/10.1159/000501906 Note that this paper uses the term gestation to mean post-conception.
  7. ^ Britten, S., Soenksen, D. M., Bustillo, M., & Coulam, C. B. (1994). Pregnancy: Very early (24–56 days from last menstrual period) embryonic heart rate in normal pregnancies. Human Reproduction, 9(12), 2424-2426. https://doi.org/10.1093/oxfordjournals.humrep.a138462
  8. ^ Tezuka, N., Sato, S., Kanasugi, H., & Hiroi, M. (1991). Embryonic heart rates: development in early first trimester and clinical evaluation. Gynecologic and obstetric investigation, 32(4), 210-212. https://doi.org/10.1159/000293033
  9. ^ Papaioannou, G. I., Syngelaki, A., Poon, L. C., Ross, J. A., & Nicolaides, K. H. (2010). Normal ranges of embryonic length, embryonic heart rate, gestational sac diameter and yolk sac diameter at 6–10 weeks. Fetal diagnosis and therapy, 28(4), 207-219. https://doi.org/10.1159/000319589
  10. ^ Tan, C. M. J., & Lewandowski, A. J. (2020). The transitional heart: from early embryonic and fetal development to neonatal life. Fetal diagnosis and therapy, 47(5), 373-386. https://doi.org/10.1159/000501906 Note that this paper uses the term gestation to mean post-conception.
  11. ^ Branum, A. M., & Ahrens, K. A. (2017). Trends in timing of pregnancy awareness among US women. Maternal and child health journal, 21(4), 715-726. https://stacks.cdc.gov/view/cdc/43985
  12. ^ Tezuka, N., Sato, S., Kanasugi, H., & Hiroi, M. (1991). Embryonic heart rates: development in early first trimester and clinical evaluation. Gynecologic and obstetric investigation, 32(4), 210-212. https://doi.org/10.1159/000293033
  13. ^ Britten, S., Soenksen, D. M., Bustillo, M., & Coulam, C. B. (1994). Pregnancy: Very early (24–56 days from last menstrual period) embryonic heart rate in normal pregnancies. Human Reproduction, 9(12), 2424-2426. https://doi.org/10.1093/oxfordjournals.humrep.a138462
  14. ^ Tezuka, N., Sato, S., Kanasugi, H., & Hiroi, M. (1991). Embryonic heart rates: development in early first trimester and clinical evaluation. Gynecologic and obstetric investigation, 32(4), 210-212. https://doi.org/10.1159/000293033
  15. ^ Tan, C. M. J., & Lewandowski, A. J. (2020). The transitional heart: from early embryonic and fetal development to neonatal life. Fetal diagnosis and therapy, 47(5), 373-386. https://doi.org/10.1159/000501906 Note that this paper uses the term gestation to mean post-conception.
  16. ^ Tan, C. M. J., & Lewandowski, A. J. (2020). The transitional heart: from early embryonic and fetal development to neonatal life. Fetal diagnosis and therapy, 47(5), 373-386. https://doi.org/10.1159/000501906 Note that this paper uses the term gestation to mean post-conception.
  17. ^ Tan, C. M. J., & Lewandowski, A. J. (2020). The transitional heart: from early embryonic and fetal development to neonatal life. Fetal diagnosis and therapy, 47(5), 373-386. https://doi.org/10.1159/000501906 Note that this paper uses the term gestation to mean post-conception.
  18. ^ Tucker, W. D., Arora, Y., & Mahajan, K. (2023). Anatomy, Blood Vessels. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK470401/
  19. ^ Tucker, W. D., Arora, Y., & Mahajan, K. (2023). Anatomy, Blood Vessels. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK470401/
  20. ^ Betz, C., Lenard, A., Belting, H. G., & Affolter, M. (2016). Cell behaviors and dynamics during angiogenesis. Development, 143(13), 2249-2260. https://doi.org/10.1242/dev.135616
  21. ^ Singh, R., & Munakomi, S. (2025). Embryology. Neural tube. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK542285/
  22. ^ Torchia, M.G., and Persaud, T.V.N (2025). The Developing Human, Clinically Oriented Embryology. Elsevier. 12th ed. p. 359
  23. ^ Sadler, T.W. (2024) Langman's Medical Embryology. 15th ed. p. 320, Fig 18.4
  24. ^ Sekulic, S., Gebauer-Bukurov, K., Cvijanovic, M., Kopitovic, A., Ilic, D., Petrovic, D., ... & Topalidou, A. (2016). Appearance of fetal pain could be associated with maturation of the mesodiencephalic structures. Journal of Pain Research, 1031-1038. https://doi.org/10.2147/JPR.S117959
  25. ^ Yang, S., Zhou, J., & Li, D. (2021). Functions and diseases of the retinal pigment epithelium. Frontiers in pharmacology, 12, 727870. https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2021.727870/full
  26. ^ Saleem, S. N. (2013). Fetal magnetic resonance imaging (MRI) a tool for a better understanding of normal and abnormal brain development. Journal of child neurology, 28(7), 890-908. https://journals.sagepub.com/doi/10.1177/0883073813486296
  27. ^ Mojsilović, J., & Zečević, N. (1991). Early development of the human thalamus: Golgi and Nissl study. Early human development, 27(1-2), 119-144. https://www.sciencedirect.com/science/article/abs/pii/037837829190033Y
  28. ^ Torchia, M.G., and Persaud, T.V.N (2025). The Developing Human, Clinically Oriented Embryology. Elsevier. 12th ed. p.242-243, Fig 12.28
  29. ^ Sadler, T.W. (2024) Langman’s Medical Embryology. Wolters Kluwer. 15th ed. p.79, Fig 6.4
  30. ^ Sadler, T.W. (2024) Langman’s Medical Embryology. Wolters Kluwer. 15th ed. p.83, Fig 6.12
  31. ^ Rehman, S., & Bacha, D. (2023). Embryology, pulmonary. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK544372/
  32. ^ Schittny, J. C. (2017). Development of the lung. Cell and tissue research, 367(3), 427-444. https://link.springer.com/article/10.1007/S00441-016-2545-0
Learn more about Gestational Age

Credentialed scientists reviewed all the material on The Voyage of Life for accuracy. Ages are listed in gestational weeks, measured from the first day of the mother’s last menstrual period, unless otherwise noted. This standard medical practice differs from post-conception age, used by embryologists and medical textbooks cited here, which starts at conception, about two weeks later.

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 May 22, 2026
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