Month 6 to 7

Response to sound, light, and maternal diet

Human Prenatal Age
  • PCW 21-25
  • 6 Months Pregnant
  • Gestational Weeks 23-27
  • The preborn baby responds to music, reading, and singing.

  • The eyes develop rods and cones and the eyes respond to changes in light.1

  • The premature infant at 22 weeks after conception sneezes when a doctor tickles his nostrils.2

  • At 23 weeks after conception, the fetal heart pumps about 375 quarts of blood each day.3

  • The fetus starts regularly using her thumb to grasp objects at 23 weeks after conception.4

  • This month is crucial for the unborn baby. Premature babies born at 21 weeks post-conception (23 weeks gestation) have a 37.4% probability of surviving through their first year, whereas babies born at 25 weeks post-conception (27 weeks gestation) have a 86.4% probability of surviving through their first year.5

The fetus reacts to loud noises with a blink-startle response starting as early as 22 weeks after conception.6 Because the fetus’s eyes are still mostly closed, some researchers have called this a “squint-startle” response. This reaction continues to develop until 30 weeks after conception and looks very similar to the startle response observed in kids and adults. Interestingly, girls tend to develop the startle response before boys.7

Methodological advances have increased the survival rates and health of babies born too early. By the middle of the sixth month, most babies who are born survive and thrive. (Image Credit: Peter K Burian, October 18, 2013, Public Domain)

The most difficult part of living outside the womb is breathing.  About 20 to 22 weeks after conception the unborn baby starts creating a substance called surfactant in the lungs.8 Surfactant’s main job is to keep the ends of the airways from sticking together when the baby exhales. By 24 to 26 weeks after conception, the future newborn makes enough surfactant on his own to survive outside the womb.9 However, doctors have developed a synthetic surfactant to help the alveoli stay open,10 and help infants survive at much younger ages. Steroids given before birth can also help the lungs mature quickly and create surfactant to increase the chance of survival.11

Breaths Per Minute
The fetus practices breathing for months before he is born. To learn more about fetal breathing patterns, researchers recorded 24 hours of continuous ultrasound from 20 fetuses between 22 and 26 weeks after conception. They found that these fetuses made breathing movements about 14% of the time and took 44 breaths per minute.12

In another study, the fetus increased his breathing rate when the mother’s blood had higher levels of carbon dioxide, just as an adult would start breathing faster with high levels of carbon dioxide in the blood.13 This shows that the mechanisms needed for a fetus to increase his breathing rate in response to blood gas levels are working in the womb.

Eye development

By 25 weeks after conception, the eyes have developed light-sensitive receptors called rods and cones.14 Rods let the eyes detect very small amounts of light, and they detect light in the periphery. By contrast, cones mostly detect light in the center of a person’s vision and produce sharp, colorful images. Adults have 100 million rods and 7 million cones in each eye.15 Cones move towards the fovea and rods move out of the fovea throughout pregnancy and into the second year after birth.16 Premature babies born 24 weeks after conception respond to light,17 as does the fetus in utero at 26 weeks after conception.18 After birth, the pupil gets smaller and bigger to let in the correct amount of light to the eye. This change in pupil size has first been observed in the fetus at 27 weeks after conception,19 and is consistently seen 31 weeks after conception in preterm infants.20

Dive Deeper
The earliest evidence of a fetus responding to sound is at 14 weeks after conception...
A child is less likely to be allergic to food that his mother consumed while she was pregnant...