The dynamic process by which the single-cell human embryo becomes a 100 trillion-cell adult is perhaps the most remarkable phenomenon in all of nature. Long before we are born, most body parts found in the adult and all body systems are present, and most routine body functions are operative. By studying human development from fertilization to birth, we can see that these body parts and systems emerge, and many routine body functions begin, at a remarkably young age and surprisingly small size. Human development is a continuous process beginning with fertilization and continuing throughout pregnancy, birth, childhood, adolescence, adulthood, and into old age. (http://www.ehd.org/dev_article_intro.php)
NOTE: Full term pregnancy typically lasts 38 weeks from conception (fertilization age, which refers to how long it has been since the day of your baby’s conception) or 40 weeks from the first day of a woman’s last normal menstrual period (LMP / gestational age, the measurement typically used by medical providers to date a pregnancy since the date of conception is often not known). As we outline the milestones of your baby’s prenatal development on this page, we will use fertilization age. Keep in mind that some of the resources we used to compile this overview of fetal development used gestational rather than fertilization age. To know when these milestones happen according to LMP, add 14 days to the baby’s fertilization age given here. Fetal lengths and weights are averages; babies are measured from crown to rump, not including legs, before 10 weeks, and after that they are measured from head to heel.
By the time a woman discovers she is pregnant, many important structures in the growing embryo have long since developed.
Baby’s Developmental Milestones
3 weeks / 21 days
Baby’s heart begins to beat.
6 weeks / 40 days
Brain activity is detectable and can be measured and recorded.
8 weeks / 56 days
Except for size, baby’s overall appearance and many internal structures closely resemble a newborn’s. Of the 4,500 permanent body parts in the adult body, 4,000 are already present.
9 weeks / 63 days
Baby sighs, stretches, and sucks thumb.
10 weeks / 70 days
Baby makes a fist around objects placed in palm (such as the umbilical cord).
11 weeks / 77 days
Baby can make complex facial expressions – even smile.
12 weeks / 84 days
Baby has all essential organs and a working circulatory system.
Baby’s entire body (except for parts of the scalp) feels and responds to light touch.
Fingerprints and toeprints are unique and complete.
Baby releases stress hormones in response to being poked with a needle.
Rapid eye movement begins, indicative of dreams.
With highly specialized medical care some babies can survive outside the womb by 20 weeks (22 LMP) with survival rates reported as high as 40% Baby now feels pain more intensely than at any other time in development because while baby’s nervous system has developed, natural pain inhibitors have not.
With intensive care, a baby born at this stage is capable of breathing air.
Primary Internet Resource
The Endowment for Human Development: http://www.ehd.org/
Prenatal Overview: http://www.ehd.org/dev_article_intro.php
Prenatal Summary: http://www.ehd.org/prenatal-summary.php (this page uses LMP / gestational age) (Detailed) Prenatal Timeline: http://www.ehd.org/science_main.php?level=i
Other resources referenced
- Anand, K. and Hickey, P. “Pain and Its Effects in the Human Neonate and Fetus.” New England Journal of Medicine, 1987.
- Anand, K., M.B.B.S., D.Phil. “Expert Report of Kanwaljeet S. Anand, M.B.B.S., D.Phil.” Expert testimony before the US Dept of Justice describing the capacity of the fetus to feel pain, Jan 14, 2004.
- Campbell, Stuart MD. Watch Me Grow! London: St. Martin’s Press, 2004.
- Carlson, B. Human Embryology & Developmental Biology. 3rd ed. Toronto: Mosby Pub, 2004.
- Ertelt, Steven. “Planned Parenthood Sues to Violate FDA Protocols, Injure Women with Dangerous Abortion Drug.” http://www.lifenews.com/2014/03/05/planned-parenthood-sues-to-violate-fda-protocols-injure-women-with-dangerous-abortion-drug/ March 5, 2014. (accessed March 23, 2014)
- Focus on the Family. “The First Nine Months.” Colorado Springs: 1999, 2008.
- La Rossa, Maureen Mulligan, RN. And Sheena L. Carter, Ph.D., “Understanding How the Brain Develops” http://www.pediatrics.emory.edu/divisions/neonatology/dpc/brain.html (accessed March 23, 2014).
- Larsen, William J. Essentials of Human Embryology. New York: Churchhill Livingstone, 1998.
- Mayo Foundation for Medical Education and Research. “Fetal development: What happens during the first (second, third) trimester?” (http://www.mayoclinic.org/healthy-living/pregnancy-week-by-week/in-depth/prenatal-care/art-20045302,
- http://www.mayoclinic.org/healthy-living/pregnancy-week-by-week/in-depth/fetal-development/art-20046151, and http://www.mayoclinic.org/healthy-living/pregnancy-week-by-week/in-depth/fetal-development/art-20045997) accessed March 23, 2014.
- Med-Health.net. “Fetal Hiccups.” http://www.med-health.net/Fetal-Hiccups.html (accessed March 23, 2014)
- Mitchell, B. and Sharma, R. Embryology. New York: Churchhill Livingstone, Dec 2004.
- Moore, K. and Persaud, T. The Developing Human, Clinically Oriented Embryology. 7th ed, Elsevier Science. Philadelphia: WB Sanders, 2003.
- Nilsson, L. and Hamberger, L. A Child Is Born. 4th ed. Vicenza: Random House, 2004.
- Tallack, Peter. In the Womb. Washington DC: National Geographic, 2006.
- O’Rahilly, R and Muller, F. Human Embryology and Teratology. 3rd ed. New York: John Wiley and Sons, Inc., 2001.
- Smith, Chris. “Murder of Newborn Babies in Infanticide as Bad as Abortion” http://www.lifenews.com/2012/03/08/murder-of-newborn-babies-in-infanticide-as-bad-as-abortion/ March 8, 2012. (accessed March 23, 2014)
- Tsiaras, A. and Werth, B. From Conception to Birth, a Life Unfolds. New York: Doubleday, 2002.
- Valman H. and Pearson, J. “What the Foetus Feels,” British Medical Journal. January 26, 1980.
- Wellcome Images: http://wellcomeimages.org/ Copyrighted work available under Creative Commons by-nc-nd 2.0 UK
- The Multi-Dimensional Human Embryo (funded by NICHD – National Institute of Child Health and Human Development) http://embryo.soad.umich.edu/index.html
- Steven O’Connor, M.D. Houston, Texas. https://www.flickr.com/photos/lunarcaustic/
- Life Issues Insititute – Windows to the Womb. http://www.lifeissues.org/windows.html
- 4d Ultrasound of Fetus 32 weeks LMP. Owner: Mrs. Flinger – Flickr image.