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 fetal heart has already beat approximately 15,800,000 times.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. This is like 6 and 1/2 gallons of milk. For comparison, an adult heart pumps 6,000 quarts of blood each day, which would likely fill a small hot tub.5

At 13 weeks after conception, the evidence points to the fetus being able to experience pain. While touch receptors cover almost all of the body, pain receptors develop later than regular touch receptors. Pain receptors develop from 8 to 15 weeks after conception, starting in the hands and the area around the mouth.6 Two neurotransmitters specific to pain processing, substance P and enkephalins, have already appeared at 8-10 weeks after conception and 10-12 weeks after conception, respectively. Furthermore, nerves connecting the primitive pain receptors with the spinal cord and thalamus can be observed as early as 13 weeks after conception.7 While the cortex may not be fully developed, a number of brain structures that process pain activity including the brainstem, insula, and thalamus, are sufficiently mature to process pain at 13 weeks after conception.8 Taken together, the evidence suggests that a fetus can now feel pain.

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)
Purposeful movements

Thirteen weeks after conception, the fetus’s entire body responds to light touch with the exception of parts of the back, buttocks, and thighs.9 The fetus also starts moving each finger separately, and often sucks his or her thumb. By 14 weeks after conception, the unborn child starts grasping objects.10 Interestingly, boys and girls move differently in the womb. In fact, girls open and close their mouths more often than boys do!11 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!12

By 12 weeks after conception, the fetus displays goal-directed movements. Before this age, the fetal movements were jerky and ballistic, but now the hands slow down as they approach their target. These intentional fetal movements show that the fetus is conscious and aware of his environment. Most of the slower, goal-directed movements were directed at the fetus’ face. However, if the fetus has a twin, he or she will move more slowly when reaching towards the twin’s face as well.13

15 Facts at 15 Weeks
Read the Report
Fetal senses

Many sensory systems start processing rudimentary information in weeks 13 & 14. The olfactory bulb, which processes smells, develops its layered structure at 12 weeks after conception.14 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.15 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.16 Each sensory system is partially developed by 13 weeks after conception.

Dive Deeper
The brain assumes its adult shape around 5 months after conception...
Sperm-egg fusion
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Sperm-egg fusion
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Sperm-egg fusion
Sperm-egg fusion
Sperm-egg fusion
Sperm-egg fusion