Charlotte Lozier Institute

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Month 7

Sleep patterns and learning

Human Prenatal Age
  • Post-conception week 26-29
  • 7 Months Pregnant
  • Gestational Weeks 28-31
  • Doctors observed varied sleep patterns in the preborn baby including rapid-eye movement (REM) and non-REM sleep.1

  • At 28 weeks, the fetus has more neurons than she will ever have again.2

  • At 28 weeks, the fetus starts smelling different odors within the amniotic fluid.3

  • By 31 weeks, the fetal heart has beat more than 40 million times.4 At this point, the fetal heart pumps 750 quarts of blood each day!5

When a woman is 7 months pregnant, scientists have a variety of tools to study the growing child while still inside the womb. The fetus’s brain activity is now strong enough to detect outside the abdomen using neuroimaging techniques like functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG).6 These techniques use blood flow or electrical signals from neurons to measure brain activity.

Researchers have used fMRI and MEG to determine that at 28 weeks, the fetal brain responds to different pitches of sound and flashes of light much the way that the adult brain responds.7 Researchers who observed premature infants at these ages also could measure brain responses to touch and pain.8

Doctors can clearly distinguish the two major kinds of sleep: REM sleep and non-REM sleep, in fetuses at 28 weeks using ultrasound technology.9 During REM sleep, a person’s eyes move rapidly under their closed lids. This sleep is important for memory formation. Non-REM sleep is often considered deeper sleep. The older the fetus, the more time he spends in REM sleep.10

Modern ultrasounds allow parents to see their unborn child in marvelous detail. (Image Credit: Science Source)
A fetus grimaces and cries in response to a painful anesthetic injection

Cutting-edge 3D ultrasound recordings have also revealed that at 31 weeks the fetus responds with different facial expressions to painful versus startling stimuli.11 Researchers examined different facial gestures before and after a fetus received an injection of anesthetic in their thigh prior to an in utero surgical procedure. The researchers compared these facial movements to those that a fetus made before and after hearing a startlingly loud noise. They found that the fetuses who received a painful injection made more horizontal and vertical mouth stretches, as a baby might make while crying, and were more likely to lower their brows and squeeze their eyes shut than the fetuses who merely got startled.12 These facial features are also associated with a conscious pain experience in newborn babies, who also cannot communicate their pain experience with words.

Watch the movie to see the fetus’s reaction to the painful injection.

(Movie Credit: Lisandra Bernardes/Pain Reports)
Impressive brain growth

The brain creates an overabundance of neurons and an overabundance of synaptic connections in a process called blooming and pruning. Just as a tree needs trimming to clear away the excess branches, synaptic pruning removes unneeded connections in the brain. At 28 weeks, the fetus has the most neurons she will ever have. For the rest of fetal development, childhood and adulthood, neurons that do not become part of useful circuits undergo programmed cell death, called apoptosis. Neurons are energy-intensive cells, so removing unhelpful neurons makes the brain more efficient. The remaining neurons also undergo periods of explosive synaptic growth, where they make thousands of connections with other neurons. Advantageous connections get stronger and useless connections deteriorate, leaving the brain with useful and efficient circuits.13

Billion Neurons
At 28 weeks, the fetus has more neurons than he will ever have again, over 100 billion neurons! Neurons that fail to integrate into meaningful brain circuits start to die off, leaving adults with 60-85 billion neurons.14

At seven months, myelination also begins. Myelination is the process of wrapping neurons in a fatty sheath to speed up their signaling. While neural circuits still function before each neuron is myelinated, myelination makes each connection in a circuit more efficient. First, the sensory systems myelinate, then the motor systems, and finally the association areas start to myelinate about 9 months after birth.15 Myelination does not end until age 25!16

Most premature babies survive

If a woman delivers her baby when she is 7 months pregnant, most of the time that baby will survive without any major disabilities. At 28 weeks gestation, at least 92% of all premature babies survive the first year. By 31 weeks, that number has risen to over 96%.17 Premature children born before 30 weeks still have significantly higher risks of vision and hearing problems, as well as lower IQs than their full-term counterparts.18

Dive Deeper
Newborns remember sounds and tastes that they experienced in the womb...