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Month 7

Smelling, hearing, and learning

Human Prenatal Age

Post-conception week 26-29
7 Months Pregnant
Gestational Weeks 28-31

Highlights

At 7 months, babies in the womb are starting to remember sounds.¹
Doctors observed varied sleep patterns in the unborn baby including rapid-eye movement (REM) and non-REM sleep.²
At 28 weeks, the unborn baby can smell different odors within the amniotic fluid.³

By 30 weeks, the baby shows clear signs of learning in the womb. The earliest form, called habituation, is a reduced response to repeated sounds or touch. Researchers observe this in diminishing startle reflexes, changes in movement, and shifts in brain activity.⁴

This composite image rendered from light-guided endoscopy recordings shows the fetus alive in the uterus 7 months after . At this age, when the mother rubs her belly, the baby starts to interact by pushing back.⁵ (Image Credit: Education Resource Fund)

When does the unborn baby start to learn?

By seven months of pregnancy, babies in the womb are not just hearing sounds — they’re starting to remember them. A small brain response occurs when a sound is new; a larger brain response shows fetal recognition of the sound and early learning. In one fascinating study, pregnant women listened to recordings that included nonsense words like “tatata” and “tatota” during their last 10 weeks of pregnancy. After birth, the babies who had heard those sounds in the womb showed larger brain responses when hearing them again — at just a few days or even a few months old!⁶ Similarly, when pregnant women repeatedly listened to recordings of “Twinkle twinkle little star” in the last 10 weeks of pregnancy, the babies who had heard that song in the womb showed larger brain responses when hearing them again right after birth or at 4 months old. They also had smaller brain responses when parts of the melody were changed.⁷

The unborn baby also starts learning what to pay attention to—and what to ignore. In one study, babies whose mothers lived near an airport for the last few months of pregnancy became so used to airplane noise in the womb that they slept through it after birth. But when they heard a new sound at the same volume, they woke up.⁸ This ability to tune out familiar, unimportant noise helps the baby focus on what is new and meaningful.

Like mother, like fetus

By 7 months of pregnancy, unborn babies appear deeply connected with their mothers. At 25 weeks gestation, unborn babies are more likely to open their mouths after their mother sings or speaks than after she makes unrelated mouth movements.⁹ Similarly, fetuses between 28 and 32 weeks gestation were more likely to yawn shortly after their mothers yawned, but not after other mouth movements. Fetal yawning often occurred about 90 seconds later, similar to contagious yawning in adults.¹⁰ Yawning begins in the womb as early as 11 weeks, but soon becomes more than a simple reflex. Instead, these tiny responses may reflect one of the earliest signs of social bonding and communication between mother and child. Furthermore, baby starts to interact with his family. At 7 months, when the mother rubs her belly, the fetus is more likely to respond by moving his hands to the uterus wall to return the touch.¹¹

Diagram showing yawning latency: A woman watches a contagious yawning video, yawns after 84.81 seconds, and a fetus yawns after 90.37 and 175.19 seconds, following the mothers yawn. Icons represent each event.

When the mother views a video of someone yawning, she often yawns about 85 seconds later in response. About 90 seconds after the mother yawns, the fetus yawns as well, demonstrating prenatal social contagion. (Image Credit: Current Biology)

At 7 months when the mother rubs her belly, the baby interacts by moving his hands to the uterus wall to return the touch.¹²

What can the baby smell in the womb?

Between 28 and 30 weeks of pregnancy, babies begin to smell — not through the air, but through the amniotic fluid.¹³ The fluid carries a mix of odors that come from the baby’s own body and from the flavors in the mother’s diet.¹⁴ Even though the baby isn’t breathing air yet, his developing nose is already at work, soaking in the scent-rich world of the womb.

Studies of premature babies provide strong evidence that the sense of smell becomes functional before birth. When exposed to the scent of mint, premature infants older than 29 weeks often became more alert or began sucking, while younger infants were less likely to respond.¹⁵ Other studies found that both preterm infants between 28 and 34 weeks could distinguish between odors such as vanilla and fennel after only brief exposure, responding more strongly to a new scent than to one they had smelled before.¹⁶ At the same ages, premature infants also increased their breathing rate when exposed to pleasant smells like vanilla but slowed their breathing and even grimaced in response to unpleasant odors, such as rancid acid, even at very low concentrations.¹⁷ Together, these findings show that fetuses and preterm infants can respond to a wide range of smells by 7 months gestation in clear and measurable ways.¹⁸

Modern ultrasounds allow parents to see their unborn child in marvelous detail. (Image Credit: Science Source)

Premature babies between 28 and 34 weeks speed up their breathing for pleasant smells like vanilla, but slow down their breathing and even grimace for unpleasant odors, like rancid acid — even at tiny concentrations. ¹⁹ ²⁰

At 7 months, the unborn baby sleeps about 65% of the time. His eyes can move rapidly under closed eyelids while he sleeps. (Image Credit: Adobe Stock Photos)

How often does the unborn baby sleep?

At 7 months, the unborn baby sleeps about 65% of the time, increasing with each month so that by the last month of pregnancy, the baby sleeps almost 85% of the time.²¹ By about 28 weeks of pregnancy, researchers can distinguish the two major types of sleep—REM and non-REM—in unborn babies using ultrasound.²² REM sleep, marked by rapid eye movements beneath closed eyelids, plays an important role in memory formation and sensory development,²³ while non-REM sleep represents deeper, quieter rest. Research suggests that the baby might be dreaming during REM sleep.²⁴ Studies tracking babies between 20 and 40 weeks gestation show that by this stage babies sleep in repeating cycles of about 45 minutes, roughly half the length of an adult sleep cycle. As the unborn baby matures, the proportion of time spent in REM sleep steadily increases.²⁵

By about 28 weeks of pregnancy, researchers can distinguish the two major types of sleep using ultrasound—REM and non-REM.²⁶ Research suggests that the baby might be dreaming during REM sleep.²⁷

A fetus grimaces and cries after a painful injection

Cutting-edge 3D ultrasound recordings have revealed that at both 23 and 31 weeks the fetus responds with different facial expressions to painful versus startling stimuli.²⁸ ²⁹ Researchers examined different facial gestures before and after an unborn baby 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.³⁰ 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.

A 31 week gestation baby grimaces and cries in response to a painful but necessary anesthetic injection. (Movie Credit: Lisandra Bernardes/Pain Reports)

Continuous ultrasounds from babies as young as 23 weeks gestation have also shown “scowling” facial expressions which may demonstrate discomfort or distress.³¹ Smiling, as well as scowling, is more frequent in older unborn babies.³² ³³ In month 7, the unborn child can pick his nose, make the “peace” sign with his fingers and blink regularly. ³⁴

The baby can spontaneously smile as early as 15 weeks gestation, but the smiles are more frequent in month 7.³⁵

Most premature babies survive

Babies born between 28 and 32 weeks of pregnancy now have an excellent chance of survival thanks to modern neonatal care. About 1 in 100 babies are born at 7 months gestation.³⁶ At 28 weeks, more than 93% survive their first year, rising to about 98% by 31 weeks.³⁷ ³⁸ ³⁹ Most survive without major disabilities.⁴⁰ Although children born before 32 weeks still face higher risks of vision, hearing, behavioral, and learning difficulties than full-term children, serious long-term complications remain relatively uncommon, affecting only about 1 in 20 children.⁴¹ ⁴²

The CDC recommends the Tdap vaccine between 27 and 36 weeks of pregnancy. (Image Credit: Airman 1st Class Alexxis Mercer)

Vaccines during pregnancy

During pregnancy, a mother shares immune protection with her baby. Antibodies in her bloodstream cross the placenta, and higher maternal antibody levels mean more protection for the fetus. For this reason, the CDC recommends the Tdap vaccine between 27 and 36 weeks of pregnancy, even if the mother has been vaccinated before. The shot boosts the mother’s antibody production, increasing the amount passed to the baby and helping shield her newborn from whooping cough after birth. A similar benefit occurs with the flu vaccine: when given late in pregnancy, it significantly reduces the risk of infection and hospitalization in infants during their first six months outside the womb.⁴³ ⁴⁴ Furthermore, when the mom receives an RSV vaccine around 8 months of pregnancy, her baby is half as likely to end up hospitalized by RSV.⁴⁵

Impressive brain growth

The brain creates an overabundance of neurons and synaptic connections, then removes the least integrated ones 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.⁴⁶ At 28 weeks, the unborn baby has more neurons than he will ever have again, over 100 billion neurons!⁴⁷ Neurons that fail to integrate into meaningful brain circuits start to die off, leaving adults with 60-85 billion neurons.⁴⁸ ⁴⁹ ⁵⁰ 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 underused connections deteriorate, leaving the brain with useful and efficient circuits.⁵¹ ⁵²

This healthy baby picks his nose while sucking on one finger at 28 weeks gestation. (Image Credit: Donaldson School Journal of Ultrasound in Obstetrics and Gynecology)

At 28 weeks, the unborn baby has more neurons than he will ever have again, over 100 billion neurons!⁵³

This healthy baby makes the "peace sign" with his fingers at 30 weeks and 1 day old. (Image Credit: Donaldson School Journal of Ultrasound in Obstetrics and Gynecology)

How do researchers study unborn babies?

When a woman is 7 months pregnant, scientists can measure the unborn baby’s brain activity from outside the womb using neuroimaging techniques like functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG).⁵⁴ 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.⁵⁵ ⁵⁶ Researchers who observed premature infants at these ages also could measure brain responses to touch, electrical stimulation,⁵⁷ flashes of light,⁵⁸ and sound.⁵⁹

The first recordings of visual-evoked responses in the brain come from fetuses at 28 weeks gestation,⁶⁰ although premature babies show brain responses to flashes of light as early as 24 weeks.⁶¹

Continued development at 7 months of pregnancy

By 31 weeks, the unborn baby’s heart has beat more than 40 million times.⁶² At this point, the fetal heart pumps 750 quarts of blood each day, enough to fill about 8 bathtubs!⁶³

Some premature infants born between 30 and 32 weeks gestation show visual attention and can fixate on objects, while others take more time to develop this skill.⁶⁴ A premature infant’s pupils will get smaller in brighter environments. This pupillary response has first been observed in preterm babies at 30 weeks, and is consistently seen after 35 weeks.⁶⁵

The amniotic fluid provides a little nutrition to the unborn baby. This month marks the highest concentration of total protein in the amniotic fluid.⁶⁶

Dive Deeper

Learning in the Womb

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

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