Weeks 19 & 20

Preparing for life outside the womb

Human Prenatal Age
  • PCW 19&20
    i
  • 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
Treating children at 21 weeks after conception has become more commonplace...