Month 8 to 9

Brain growth and lung maturation

Human Prenatal Age
  • PCW 30-33
    i
  • 8 Months Pregnant
  • Gestational Weeks 32-35
Highlights
  • At 30 weeks after conception, the fetus practices breathing almost 40% of the time.1

  • At 32 weeks after conception, the fetal heart pumps about 990 quarts of blood each day.2

  • By 32 weeks after conception, true alveoli start forming in the lungs. About 95% of the true alveoli develop after birth. Children keep growing true alveoli until age 8.3 

  • Although in boys, the testicles develop 12 weeks after conception, they remain in the abdomen until 33 weeks after conception. Then they descend into the scrotum.4 

The creation of synapses between neurons peaks 32 weeks after conception.5 Simultaneously, the fetus’s ability to recognize familiar songs and stories improves dramatically.6

40000
Synapses / Second
At their peak, neurons create 40,000 new synapses every second!7 After birth, many of these synapses will be eliminated as the brain supports the survival of neurons and synapses that efficiently transmit messages, while the unnecessary neurons and synapses are removed.8

This month, the brain develops many bumps and grooves, called gyri and sulci.9 These bumps and grooves increase the surface area of the brain, which is important because the cortex is only on the surface of the brain. By adding gyri and sulci all over, the brain can pack in more cortical neurons than it otherwise could. This explosive brain growth is accompanied by huge advances in fetal learning capabilities.

At this point, the baby makes a variety of facial expressions. His eyelids open and close, and his eyes move rapidly while he sleeps. (Image Credit: Science Source)
When does the fetus start to learn?

Although the fetus is actively sensing his world for most of the pregnancy, he only starts to show measurable signs of recognition around 30 weeks after conception.10 Specifically, researchers can measure recognition in utero by examining changes in fetal heartrate. In the third trimester, the fetus usually responds to non-startling sounds with a mild deceleration in heartrate. The fetus will respond to a familiar sound with a larger heartrate deceleration than she will respond to an unfamiliar sound. When mothers read a rhyme aloud daily, it took 26-week post-conception fetuses about 5 weeks to become familiar with the rhyme. However, it only took 30-week post-conception babies 2 weeks to become familiar with the rhyme, showing that sound recognition dramatically improves between 26 and 30 weeks after conception.11

This premature baby benefits from skin time. The mother’s body helps regulate his temperature and reduce stress hormones. Over 98% of babies born in this month survive.12 (Image Credit: Sathishsugavanam27, 29 January 2019)

At birth, newborns prefer looking at faces compared to upside-down faces or other images. Scientists also wondered whether postnatal experience was important for this preference. To answer this question, one research group decided to project patterned light from outside the mother into the womb. Red lasers projected three dots into the womb – one set of dots that looked like a face, with eyes and a mouth, and another set upside-down. Amazingly, at 32 weeks after conception, the fetuses turned their heads toward the face-like lights projected through the uterine wall, and turned less when the dots were upside-down.13 This shows that not only can the fetus see and respond to visual information from outside the womb, the fetus also prefers looking at face-like stimuli.

By this point, the fetus also grasps objects that come near her hands. In fact, as early as 25 weeks after conception, the fetus can hold her own body weight momentarily by grasping.14

Dive Deeper
By 26 weeks, the fetus can distinguish between different smells in the amniotic fluid...