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

Weeks 19 & 20

Preparing for life outside the womb

Human Prenatal Age
  • PCW 19&20
    i
    Post-Conception Weeks
  • 5-6 Months Pregnant
  • Gestational Weeks 21&22
Highlights

  • By 20 weeks after conception the inner ear has developed. The baby moves after hearing a loud, low-pitched sound, such as her father’s voice.1

  • The left and right sides of the brain show differences as early as 20 weeks.2

  • The fetus responds to taste, temperature, pain, pressure, movement, and light with changes in heart rate and movement patterns.3

Between the beginning and the end of the fifth month, the fetus prepares for life outside of the womb. Babies as young as 19 weeks after conception (21 weeks gestation) have survived.4 Many American hospitals have started offering resuscitation and active care for infants born at 20 and 21 weeks after conception (22 and 23 weeks gestation).

Starting in the fifth month, the fetus’s movements and breathing follows a daily cycle, called a circadian rhythm.5 Interestingly, fetal activity, especially breathing movements, increases about two hours after the mother eats, and then starts to decrease.6 The fetal heart rate follows a daily pattern as well.7

By examining continuous ultrasounds of fetuses between 18 and 38 weeks after conception, researchers found that the fetus shows periods of wakefulness, and that she sleeps in cycles of about 45 minutes, or half the length of an adult sleep cycle.8

In females, the number of future eggs in the ovary peaks around 7 million at 19 weeks after conception. After this, the ovary essentially stops creating oogonia, and about 5 million of these cells die before birth. The remaining oogonia produce several thousand primary oocytes, or egg cells.9

Every detail of the human face comes together with flawless precision, following the genetic blueprint laid forth in the zygote. (Image Credit: Priests for Life)
Dive Deeper
Saving Extremely Premature Babies
Treating children at 21 weeks after conception has become more commonplace...
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Sources
  1. Peter G Hepper and B Sara Shahidullah, “Development of Fetal Hearing,” Archives of Disease in Childhood - Fetal and Neonatal Edition 71, no. 2 (September 1, 1994): F81, https://doi.org/10.1136/fn.71.2.F81.
  2. Daniel R. Weinberger et al., “Asymmetrical Volumes of the Right and Left Frontal and Occipital Regions of the Human Brain,” Annals of Neurology 11, no. 1 (1982): 97–100, https://doi.org/10.1002/ana.410110118.
  3. Lecanuet, Jean-Pierre, and Benoist Schaal. “Fetal Sensory Competencies.” European Journal of Obstetrics & Gynecology and Reproductive Biology 68 (September 1996): 1–23. https://doi.org/10.1016/0301-2115(96)02509-2.
  4. George Franco, “Extreme Preemie Born at 21 Weeks Young at Emory Decatur Hospital,” Text.Article, FOX 5 Atlanta (FOX 5 Atlanta, December 26, 2019), https://www.fox5atlanta.com/news/extreme-preemie-born-at-21-weeks-young-at-emory-decatur-hospital.; “Baby Richard Born at 21 Weeks: One of the Youngest Babies to Survive,” Children’s Minnesota, December 23, 2020, http://www.childrensmn.org/2020/12/23/baby-richard-born-21-weeks-one-youngest-babies-survive/.; Kaashif A. Ahmad et al., “Two-Year Neurodevelopmental Outcome of an Infant Born at 21 Weeks’ 4 Days’ Gestation,” Pediatrics 140, no. 6 (December 2017): e20170103, https://doi.org/10.1542/peds.2017-0103.
  5. J. I. de Vries et al., “Diurnal and Other Variations in Fetal Movement and Heart Rate Patterns at 20-22 Weeks,” Early Human Development 15, no. 6 (November 1987): 333–48, https://doi.org/10.1016/0378-3782(87)90029-6.
  6. J. I. de Vries et al., “Diurnal and Other Variations in Fetal Movement and Heart Rate Patterns at 20-22 Weeks,” Early Human Development 15, no. 6 (November 1987): 333–48, https://doi.org/10.1016/0378-3782(87)90029-6.
  7. J. I. de Vries et al., “Diurnal and Other Variations in Fetal Movement and Heart Rate Patterns at 20-22 Weeks,” Early Human Development 15, no. 6 (November 1987): 333–48, https://doi.org/10.1016/0378-3782(87)90029-6.
  8. T. Okai et al., “A Study on the Development of Sleep-Wakefulness Cycle in the Human Fetus,” Early Human Development, Advances in Perinatal Medicine Proceedings of the First International Congress of Perinatal Medicine, 29, no. 1 (June 1, 1992): 391–96, https://doi.org/10.1016/0378-3782(92)90198-P.
  9. O’Rahilly, R, and F Mueller. Human Embryology and Teratology. 3rd ed. Wiley-Liss, 2001.
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 August 29, 2022
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