Human Heart and Brain Development
From its inception when sperm and egg fuse to the pinnacle of adulthood, human life develops according to the intricate craftsmanship of a divine Creator. The unfolding of cells into diverse tissues and the orchestration of complex structures into their correct locations underscore the profound complexity of embryonic development. Central to this process is the formation of the brain, a marvel of intricacy and precision. From its earliest stages, the brain exhibits a remarkable capacity for growth and refinement, sculpting neural circuits that underpin cognition and sensation. The experiences of the fetus also shape sensory development, illustrating the intricate interplay between biology and environment. Learning some of the details of cardiac and neurological development can help us better comprehend the unique dignity of each individual.
As we begin growing from a single cell, layers and structures form and fold like a glorious origami. How do the cells all become different types of tissue, assemble into the correct structures, and work together to serve our body and sustain life? Why does the cornea of the eye develop transparently, while the whites of our eyes block incoming light? Why do arteries develop so much thicker than veins, and how does blood flow correctly through the human heart? How do the genetic instructions we are given perform so successfully—lining our stomachs, for example, with mucus so that the digestive enzymes do not leak into our bodies? The mysteries multiply, especially when we turn to the human brain. The infant brain has about 100 billion neurons, each forming thousands of connections with other neurons. The wonder of fetal development points like a spotlight to a gifted Creator in Heaven. Human life is sacred for two fundamental reasons. First, God set human beings apart from the rest of creation to reflect and bear His image. By fashioning humanity in His own likeness, He imparted within us a mark of the divine that renders us irreplaceable and deserving of utmost dignity and respect. Thus, from the very moment of conception, each individual bears God’s image. The genetic variation in each person further underscores the uniqueness of every human life, ensuring that no two individuals are, or ever will be, genetically identical.1 Second, the sacredness of human life stems from God’s unconditional love for each person as an individual, exemplified in Jesus’ parable of the lost sheep. This divine affection extends even to the preborn, since it is God who winds together our DNA and knits muscles, nerves, and enzymes together in the womb. Therefore, God also loves the child aborted in a quiet hospital room—we are told that He numbers the hairs on her head, and He is equally capable of numbering each heartbeat before the preborn child’s violent and untimely death. Being pro-life is not about having the correct views. It is about acting as the hands and feet of Jesus to find the lost sheep by loving and protecting unseen individuals.
The Beating Heart
The heart is the first organ to function in the developing human embryo.2 By six weeks’ gestation, every living human has a beating heart. By 22 days after sperm-egg fusion, the heart rhythmically pumps fluid, and this rhythmic pumping does not stop until death.3 From the sixth week of gestation onwards, the embryonic heart outpaces the mother’s heart. While the average adult heart rate ranges from 60 to 100 beats per minute, the embryonic heart beats at approximately 110 beats per minute by the sixth week and increases to around 170 beats per minute by the tenth week gestation.4 Consequently, by the end of the sixth gestational week, the heart will already have beaten over 1 million times, and by birth will have beaten approximately 54 million times.5
The preborn child’s heart is crucial for growth. Initially, cells rely on passive diffusion from the placenta for oxygen and nutrients. However, as the embryo grows, the distance increases, requiring the heart to circulate oxygen-rich blood and nutrients.6
At six weeks’ gestation, the heart emerges as two tubes, which fuse together and fold, forming an s-curve. Already the heart begins to form primitive heart valves to prevent the backflow of blood and help push the blood forward through the rest of the body.7 In the seventh week, the two upper sections become the atria, and in the eighth week the larger, stronger ventricles form. The heart reaches its final shape by the tenth week, with two atria, two ventricles, and circulatory blood vessels, although these blood vessels mostly bypass the liver and lungs to help the embryo get oxygenated blood from the umbilical cord to the rest of the body.8 Although the six-weeks’ gestation heart tube does not look like an adult heart, it performs the same function.
In the doctor’s office, recognizing the fetal heartbeat through ultrasound technology is a pivotal moment. It’s not merely “electrical activity in the fetal pole,” as some pro-abortion voices would dismiss it. Rather, it’s the rhythmic pulsation of life-sustaining blood coursing through the developing embryo. A Doppler ultrasound picks up the movement of blood within the heart. Just as your smartphone captures light to create a selfie, ultrasound harnesses reflected sound waves to paint a vivid picture of the growing life within. The reality of a selfie isn’t diminished by being a product of reflected light; likewise, the heartbeat resonating through the embryo is no less real because it results from reflected sound waves.
Developing a Brain
Our abilities to remember, perceive, and decide unfold within the sanctity of the womb, as do our abilities to sense our body in space, hear, smell, see, and feel. In the fifth gestational week, the brain starts forming as the neural tube. From this humble beginning, the top regions of the neural tube expand and delicately fold to create the brain. Chemical signaling guides brain structures to form in their designated places with miraculous precision. By approximately five and a half months into gestation, the brain takes on its adult shape. During the following months, its previously smooth surface becomes intricately contoured, expanding its surface area to accommodate the burgeoning number of neurons.9
Neural stem cells play a pivotal role in generating a diverse array of neurons and glial cells, each with a specific function in the orchestration of thought and sensation. Originating deep within the brain, emerging neurons migrate to sculpt the cortex, with the timing of their birth determining their ultimate purpose. Meanwhile, complex chemical messages facilitate communication between neurons, guiding the formation of connections crucial for cognition.10 Electrical activity has been recorded from an embryo as early as eight weeks’ gestation, indicating that neurons are actively connecting.11 As pregnancy progresses, more neural circuits rapidly form, laying the groundwork for more cognitive abilities.
Even before leaving the womb, the preborn child can sleep, taste, smell, move intentionally, learn flavors and songs, and recognize his mother’s voice.12
But the odyssey of neural development does not end with birth. Rather, it is a lifelong journey of growth and refinement. Like a sculptor refining a masterpiece, the brain undergoes a process of blooming and pruning, shedding redundant connections to sculpt a more efficient neural architecture. For instance, by 28 weeks’ gestation, a fetus harbors more neurons than she will ever possess again, as surplus neurons are systematically eliminated.13
Likewise, two-year-olds have more synapses than adults; but these extra synapses are often detrimental. Part of the reason that babies lurch haltingly as they learn to walk is that multiple neurons try to control a single muscle, and these neurons do not coordinate their efforts.14
Developing a Brain That Perceives
Fetal experiences significantly influence sensory development. This is why certain senses like taste, hearing, and touch are more advanced at birth than, for example, vision. For instance, because fetuses can hear their mother’s voices, as newborns they can recognize their mother’s native language.15 Additionally, because fetuses can taste flavors from their mother’s diet in the amniotic fluid, newborns can identify the mother’s breastmilk without ever having tasted it, by associating it with flavors they experienced in their amniotic fluid.16 In contrast, there is much less opportunity to develop the sense of sight before birth: Limited light penetrates the uterus, so newborns are born legally blind.17
Each sensory system develops in an intricate and interactive way. Take taste, for example. Nascent taste buds start forming on the tongue around eight weeks’ gestation, about a month after a mother might first know she is pregnant. For these taste buds to work, they must connect to a specialized sensory nerve to relay the taste information to the brain. Through an interplay of chemical messages between cells, a taste bud only matures after it has appropriately connected to one of these nerves.18 The fetus can taste at about four and a half months gestation.19 Every human has spent about five months of his or her life drinking nothing but amniotic fluid. When a mother eats something, the flavors of the food arrive in the amniotic fluid about 45 minutes later.20 The preborn child will swallow more amniotic fluid if it is sweet and less if it is bitter.21 The flavors that a fetus tastes in the womb will even influence her food preferences when she later starts solid foods. For example, mothers who drank carrot juice regularly during the eighth month of pregnancy gave birth to babies who made happier facial expressions while eating carrot-flavored cereal once they started eating solid foods.22
Fetal Pain Development
Touch and pain systems also develop in an intricate and interactive way. Recent evidence indicates that preborn babies can feel pain as early as 15 weeks’ gestation, challenging outdated beliefs.23 A recent review conducted by two esteemed medical professionals, one of whom identifies as prochoice, concluded that fetuses may be able to feel pain as early as 12 weeks’ gestation.24 In contrast to earlier claims that pain was not possible until the cortex had formed, these authors conclude, “Nevertheless, we no longer view fetal pain (as a core, immediate, sensation) in a gestational window of 12–24 weeks as impossible based on the neuroscience.”25 Importantly, the review provided evidence that neural connections from the periphery to the brain are functionally complete after 18 weeks’ gestation.26 Though we cannot know if fetal pain is equivalent to adult pain, the available scientific data indicate that such functional sensation is present, along with its moral implications.
The circuits underlying pain sensation start developing early. Touch and pain receptors start forming at seven and a half weeks’ gestation, starting near the mouth and hands. These sensory nerves immediately begin forming connections with the young spinal cord.27 Functionally, the embryo will reflexively move away from a touch at seven and a half weeks.28 Nerve connections linking the pain receptors to the brain’s thalamus and subcortical plate are formed between 12 and 20 weeks gestation.29 The thalamus, which plays a pivotal role in adult pain perception, functions in fetal pain sensation as well.30 Neurotransmitters dedicated to pain, such as substance P and enkephalin, appear at 10 to 12 weeks and 12 to 14 weeks respectively.31
Technological advancements, particularly ultrasonographic studies, offer unprecedented insights into fetal responses to pain. The fetus responds to a painful procedure with a stress response that includes an increase in his circulating stress hormones and “vigorous body and breathing movements” by 18 weeks’ gestation.32 Furthermore, ultrasound videos show actions indicating crying out in the womb during an anesthetic injection as early as 23 weeks’ gestation.33 Finally, the younger a premature baby is, the greater the baby’s brain response to a painful heel lance, suggesting that both fetuses and premature children are more sensitive to pain than full-term newborns and adults.34 Taken together, a number of studies demonstrate that the developing fetus is sensitive to pain inside the womb, and potentially more sensitive to pain than a newborn.
Furthermore, fetal surgeries are now routinely performed, and they incorporate anesthesia and analgesia protocols to alleviate potential fetal suffering. Fetal surgeries may occur as early as 15 weeks’ gestation to correct genetic anomalies or help both twins develop healthfully in twin-to-twin transfusion syndrome.35 Importantly, the medical consensus concludes that from the fifteenth gestational week onward, “the fetus is extremely sensitive to painful stimuli,” making it “necessary to apply adequate analgesia to prevent [fetal] suffering.”36 Expectant mothers undergoing prenatal surgery are informed of the measures taken to ensure fetal comfort and pain management during procedures, underscoring medical recognition of preborn babies as patients deserving of compassionate care.
Developing a Brain That Decides
Every impulse, every choice, every subtle movement stems from the miraculous complexity of the developing brain. At 14 weeks’ gestation, pioneering research has uncovered that the fetus demonstrates intentional movements, directing gestures more slowly toward her own eyes, mouth, and even the uterine wall.37 Before this milestone, fetal movements are characterized by erratic, jerky motions. However, at this juncture, the hands deliberately slow down as they approach their target. Notably, in cases where the fetus shares the womb with a twin, certain movements are directed towards the sibling, and these are executed with unexpected gentleness at 14 weeks’ gestation as well.38 By 18 weeks, this dexterity becomes even more pronounced, with the fetus exhibiting swifter and more precise gestures towards her own features, particularly when using her dominant hand.39
Better than Belief
No one but God knows the exact moment when a sperm and egg united within the fallopian tube of my friend Noor, creating a new life. Noor was an independent businesswoman with her own dance studio. She loved to dress up and stay out late dancing! Her positive pregnancy test left her feeling upset and confused: Babies are inconvenient. They don’t let you go out all night. As her son’s heart started beating, Noor fought off waves of nausea. As her son started tasting the amniotic fluid, Noor became more limited in dance instruction. Some people advised Noor to get an abortion. But Noor chose life. Her son was born two days before my daughter in the same hospital. Noor babysat for me frequently, and our children are good friends. I can’t imagine a world without her son’s laughter. But Noor’s very hip lifestyle was permanently altered by raising a child. Her chic apartment became littered with kid toys, wet burp cloths, and unmatched socks, but her life was also enriched in ways she had never imagined. I don’t know Noor’s views on whether abortion should be legal. But her courageous sacrifices make her one of the most pro-life people I’ve ever met.
Being pro-life is not about having the correct views. It is about acting as the hands and feet of Jesus to love the least, the lost, and the lonely. Spending time in awe and wonder at the precision of neurological development in the womb is very important, as it guides us to stand in awe of our Creator and recognize that life is sacred at every stage. But that is not enough. God has called all of us to love the woman who gets to nurture a sacred life in her womb, and support both lives with dignity and value.
NOTES
1. National Institutes of Health (US) and Biological Sciences Curriculum Study, Understanding Human Genetic Variation, NIH Curriculum Supplement Series. (National Institutes of Health (US), 2007), https://www.ncbi.nlm.nih.gov/books/NBK20363/.
2. 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.
3. 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
4. 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.
5. EHD: Appendix. “Appendix | Prenatal Overview.” Accessed April 3, 2020. https://www.ehd.org/ dev_article_appendix.php
6. Hill, M.A. (2023, January 28), Cardiovascular System Development, Available at: https:// embryology.med.unsw.edu.au/embryology/index.php/Cardiovascular_System_Development
8. Buijtendijk, MFJ, Barnett, P, van den Hoff, MJB. Development of the human heart. Am J Med Genet Part C. 2020; 184C: 7– 22. https://doi.org/10.1002/ajmg.c.31778.
9. Konkel Lindsey, “The Brain before Birth: Using FMRI to Explore the Secrets of Fetal Neurodevelopment,” Environmental Health Perspectives 126, no. 11 (2018): 112001, https://doi. org/10.1289/EHP2268.
10. Kristin Keunen, Serena J. Counsell, and Manon J. N. L. Benders, “The Emergence of Functional Architecture during Early Brain Development,” NeuroImage, Functional Architecture of the Brain, 160 (October 15, 2017): 2–14, https://doi.org/10.1016/j.neuroimage.2017.01.047.
11. Borkowski, Winslow J., and Richard L. Bernstine. “Electroencephalography of the Fetus.” Neurology 5, no. 5 (May 1, 1955): 362. https://doi.org/10.1212/WNL.5.5.362.
12. https://lozierinstitute.org/voyage/
13. Rachel Marsh, Andrew J. Gerber, and Bradley S. Peterson, “Neuroimaging Studies of Normal Brain Development and Their Relevance for Understanding Childhood Neuropsychiatric Disorders,” Journal of the American Academy of Child & Adolescent Psychiatry 47, no. 11 (November 1, 2008): 1233–51, https://doi.org/10.1097/CHI.0b013e318185e703.
14. https://lozierinstitute.org/dive-deeper/brain-connections-for-movement-and-sensations/
15. https://lozierinstitute.org/dive-deeper/the-newborn-senses-hearing/
16. K. Mizuno et al., “Mother-Infant Skin-to-Skin Contact after Delivery Results in Early Recognition of Own Mother’s Milk Odour,” Acta Paediatrica (Oslo, Norway: 1992) 93, no. 12 (December 2004): 1640–45, https://doi.org/10.1080/08035250410023115.
17. https://lozierinstitute.org/dive-deeper/the-newborn-senses-sight-and-eye-color/
18. Witt, M., and K. Reutter. “Embryonic and Early Fetal Development of Human Taste Buds: A Transmission Electron Microscopical Study.” The Anatomical Record 246, no. 4 (December 1996): 507–23. https://doi.org/10.1002/(SICI)1097-0185(199612)246:4<507::AID-AR10>3.0.CO;2-S.
19. https://lozierinstitute.org/dive-deeper/fetal-taste-and-maternal-diet/
20. Mennella, J., Johnson, A. and Beauchamp, G. “Garlic Ingestion by Pregnant Women Alters the Odor of Amniotic Fluid,” Chemical Senses 20, no. 2 (April 1, 1995): 207–9, https://doi.org/10.1093/ chemse/20.2.207.
21. Liley, A. W. “The Foetus as a Personality.” The Australian and New Zealand Journal of Psychiatry 6, no. 2 (June 1972): 99–105. https://doi.org/10.3109/00048677209159688.
22. Mennella, Julie A., Coren P. Jagnow, and Gary K. Beauchamp. “Prenatal and Postnatal Flavor Learning by Human Infants.” Pediatrics 107, no. 6 (June 2001): E88. https://doi.org/10.1542/ peds.107.6.e88.
23. https://lozierinstitute.org/dive-deeper/prenatal-stress-and-pain/
24. Derbyshire, Stuart WG, and John C Bockmann. “Reconsidering Fetal Pain.” Journal of Medical Ethics 46, no. 1 (January 2020): 3–6. https://doi.org/10.1136/medethics-2019-105701.
25. Ibid.
26. Ibid.
27. Humphrey, Tryphena. “Some Correlations between the Appearance of Human Fetal Reflexes and the Development of the Nervous System.” In Progress in Brain Research, edited by Dominick P. Purpura and J. P. Schadé, 4:93–135. Growth and Maturation of the Brain. Elsevier, 1964. https://doi. org/10.1016/S0079-6123(08)61273-X.
28. Humphrey, Tryphena. “Some Correlations between the Appearance of Human Fetal Reflexes and the Development of the Nervous System.” In Progress in Brain Research, edited by Dominick P. Purpura and J. P. Schadé, 4:93–135. Growth and Maturation of the Brain. Elsevier, 1964. https://doi. org/10.1016/S0079-6123(08)61273-X.
29. Derbyshire, Stuart WG, and John C Bockmann. “Reconsidering Fetal Pain.” Journal of Medical Ethics 46, no. 1 (January 2020): 3–6. https://doi.org/10.1136/medethics-2019-105701.
30. Chien JH et al., Human Thalamic Somatosensory Nucleus (Ventral Caudal, Vc) as a Locus for Stimulation by INPUTS from Tactile, Noxious and Thermal Sensors on an Active Prosthesis. Sensors (Basel). 17, 2017.
31. Bellieni, Carlo V. “Analgesia for Fetal Pain during Prenatal Surgery: 10 Years of Progress.” Pediatric Research, September 24, 2020, 1–7. https://doi.org/10.1038/s41390-020-01170-2.
32. Giannakoulopoulos, X., Teixeira, J., Fisk, N., & Glover, V. (1999). Human fetal and maternal noradrenaline responses to invasive procedures. Pediatric research, 45(4), 494-499.
33. Bernardes, L. S., Rosa, A. S., Carvalho, M. A., Ottolia, J., Rubloski, J. M., Castro, D., & de Andrade, D. C. (2021). Acute pain facial expressions in 23-week fetus. Ultrasound in Obstetrics & Gynecology. https://doi.org/10.1002/uog.23709 and https://lozierinstitute.org/wp-content/ uploads/2022/08/pr9_2020_11_25_diandrade_painreports-d-20-0059_sdc1b.mp4
34. Marco Bartocci et al., “Pain Activates Cortical Areas in the Preterm Newborn Brain,” PAIN 122, no. 1 (May 1, 2006): 109–17, https://doi.org/10.1016/j.pain.2006.01.015.
35. David Baud et al., “Fetoscopic Laser Therapy for Twin-Twin Transfusion Syndrome before 17 and after 26 Weeks’ Gestation,” American Journal of Obstetrics and Gynecology 208, no. 3 (March 1, 2013): 197.e1-197.e7, https://doi.org/10.1016/j.ajog.2012.11.027; L. Lecointre et al., “Fetoscopic Laser Coagulation for Twin–Twin Transfusion Syndrome before 17 Weeks’ Gestation: Laser Data, Complications and Neonatal Outcome,” Ultrasound in Obstetrics & Gynecology 44, no. 3 (2014): 299–303, https://doi.org/10.1002/uog.13375.
36. Sekulic S et al. Appearance of fetal pain could be associated with maturation of the mesodiencephalic structures. Journal of Pain Research 9, 1031-1038, 2016, DOI: 10.2147/JPR. S117959.
37. Umberto Castiello et al., “Wired to Be Social: The Ontogeny of Human Interaction,” PLOS ONE 5, no. 10 (October 7, 2010): e13199, https://doi.org/10.1371/journal.pone.0013199.
38. Ibid and https://lozierinstitute.org/fetal-development/week-14/
39. Valentina Parma et al., “The Origin of Human Handedness and Its Role in Pre-Birth Motor Control,” Scientific Reports 7, no. 1 (December 1, 2017): 16804, https://doi.org/10.1038/s41598017-16827-y.
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Original Bio:
Katrina Furth is an associate scholar at the Charlotte Lozier Institute in Washington, DC, which promotes science and statistics for pro-life causes. She specializes in communicating science concepts with non-scientific audiences and is the lead author of the VoyageofLife.com website. Since graduating with a PhD in Neuroscience from Boston University, she has worked as an adjunct professor at Catholic University in Washington, DC, where she currently resides with her husband and four children.
