Although the fetus used to move away when something touched his face, the fetus now rotates his head towards things that touch his face while simultaneously closing his mouth.7 These movements mark the start of the rooting reflex, which helps a newborn find his mother’s nipple during breastfeeding.
Weeks 19 & 20
Breathing, crying, and the rooting reflex
- Post-conception week 17&18
- 5 Months Pregnant
- Gestational Weeks 19&20
Multiple research studies confirm that the fetus responds to painful stimuli with a stress response that includes recoiling and releasing stress hormones. These hormones are separate from the mother’s stress response.1
The skin has developed sweat glands.2
By 19 weeks, the fetal heart has beat over 20 million times.3
The fetal heart pumps about 55 quarts of blood each day.4
Although the eyelids are fused shut between 10 and 26 weeks, the eyes keep developing. The back of the eye, called the retina, which converts light into neural signals, now has discrete layers, each with a different main type of cell.11
In animals, waves of spontaneous electrical activity cross the retinas. This allows the retinal cells to properly connect to the visual cortex in the brain, and to organize inputs from the right and left eyes.12 Although these spontaneous retinal waves have never been directly measured from the human fetus, they likely begin around this age.
No one knows exactly when the fetus starts feeling pain, but scientists infer when the fetus feels pain using three main measures:
- Ultrasounds of fetal facial expressions. The earliest recorded grimace in response to a painful injection came from a 23-week fetus.13
- Increases in the circulating stress hormones in a fetus’s bloodstream. The earliest recordings showing that stress hormones increase after a painful blood transfusion come from fetuses as young as 18 weeks. 14
- The existence of pain sensors in the fetal skin that connect to brain circuits. By examining the connections between neurons, and the growth of brain structures that process pain in adults, researchers can predict when the fetus starts responding to pain. Cutting-edge research and reviews of peer-reviewed literature have demonstrated that the fetus may start feeling pain as early as 12 weeks, and definitely by 15 weeks.15
Many of the brain connections for processing pain have developed by 20 weeks. Specifically, neural connections between the brain and the rest of the body are functionally complete after 18 weeks.16 Furthermore, two important brain structures for processing pain include the diencephalon and the thalamus. The diencephalon is sufficiently developed at 15 weeks to create a pain experience,17 and the thalamus is sufficiently developed at 17 weeks to transmit pain information.18
Information from all of the senses, except smell, makes a neural connection in the thalamus before moving to the cortex for further processing. Decision making, perception, and language are all controlled by the cortex. None of these skills are fully developed at birth, and neither is their underlying brain structure. Before the cortex starts forming, a transitional structure called the subplate forms. This temporary and functional structure can be found in the developing brain between 12 and 35 weeks, and has the capacity to process some pain information.19 Taken together, the current science shows that the fetus can feel pain well before 20 weeks.