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Month 6

Response to sound, light, and maternal diet

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

  • At 25 weeks, the fetal heart pumps about 375 quarts of blood each day.1

  • This month is crucial for the preborn baby. Premature babies born at 22 weeks gestation have a 18.9% probability of surviving through their first year, whereas babies born at 25 weeks gestation have a 81.7% probability of surviving through their first year.2

The fetus reacts to loud noises with a blink-startle response starting as early as 24 weeks gestation.3 Because the fetus’s eyes are still mostly closed, some researchers have called this a “squint-startle” response. This reaction continues to develop until 32 weeks and looks very similar to the startle response observed in kids and adults.

Interestingly, girls tend to develop the startle response before boys.4 Furthermore, fetal movements recorded at these ages had little predictive value for a baby’s motor development and behavior for the first two years of life. However, the more boy fetuses moved at 36 weeks, the more they moved as one-year-olds. Interestingly, the opposite effect was observed for girls.5

Furthermore, at 25 weeks, the fetus starts regularly using her thumb to grasp objects.6 At six months, doctors have also studied premature infants to learn more about the capabilities of their counterparts in the womb. At 24 weeks, a premature infant sneezes when a doctor tickles his nostrils.7

Methodological advances have increased the survival rates and health of babies born too early. By the middle of month six, 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.  Around 22 to 24 weeks the preborn 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 26 to 28 weeks, 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 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 24 and 28 weeks. 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.

How does prematurity affect visual development?

By 6 months, the eyes have developed light-sensitive receptors called rods and cones.14 Rods let the eyes detect very small amounts of light. 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 Rods and cones are formed all over the retina, but in adults, rods are mostly found in the periphery and cones are found in the center of the retina, called the fovea. Interestingly, cells stop dividing in the fovea around 16 weeks gestation, and cells stop dividing in the periphery around 31 weeks.16 Cones move towards the fovea and rods move out of the fovea throughout pregnancy and for many months after birth.17 In fact, cones continue to mature until at least 4 years old.18

The visual system is functional by month 6. Premature babies born at 26 weeks show a brain response to light,19 as does the fetus in utero at 28 weeks.20 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 31 weeks,21 and is seen after 33 weeks in preterm infants.22

Although premature infants get extra visual stimulation compared to babies born near their due date, this extra experience does not help them see better. In fact, preterm infants have slower visual development, so that by 7 months old, their acuity is poorer than kids conceived at the same time.23 Also, premature babies can cry with tears, but tend to have less tears than babies born near their due date.24

Dive Deeper
The fetus starts responding to sound at 16 weeks gestation...
A child is less likely to be allergic to food that his mother consumed while she was pregnant...