Weeks 13 & 14

Sensory systems and sensations

Human Prenatal Age
  • PCW 13&14
    i
  • 4 Months Pregnant
  • Gestational Weeks 15&16
Highlights
  • Eyebrows have formed.1 

  • The fetus will swallow more amniotic fluid if the amniotic fluid tastes sweet, and less if it tastes bitter.2

  • The stomach lining reaches its mature structure and secretes digestive enzymes into swallowed amniotic fluid.3

  • More of the preborn baby’s skeleton hardens from cartilage into bone. If a doctor took an X-ray this week, the fetus’s skeleton would be visible.4

  • The preborn baby’s circulatory system pumps about 26 quarts of blood per day at 13 weeks after conception. For comparison, an adult heart pumps 6,000 quarts of blood each day.5

Thirteen weeks after conception, the fetus’s entire body responds to light touch with the exception of parts of the back, buttocks, and thighs.6 The fetus also starts moving each finger separately.7 Interestingly, boys and girls move differently in the womb. In fact, girls open and close their mouths more often than boys do!8

This fetus could taste the amniotic fluid within the amniotic sac. When the fluid was sweet, he swallowed more than when it was bitter. (Image Credit: Priests for Life)

Until this point, the fetus has been mostly stoic. Now the preborn child produces complex facial expressions. According to some research groups, the fetus can even smile! 9

Many sensory systems start processing rudimentary information in these weeks. The olfactory bulb, which processes smells, develops its layered structure at 12 weeks after conception.10 Tastebuds start clustering in functional taste pores and connecting to cranial nerves 12-13 weeks after conception, making it likely that the fetus tastes the amniotic fluid by 13 weeks after conception.11 In fact, 13-14 weeks after conception, the fetus will swallow more amniotic fluid if the amniotic fluid tastes sweet, and less if it tastes bitter.12

Dive Deeper
The brain assumes its adult shape around 5 months after conception...