At five months of pregnancy (roughly 18 to 22 weeks), a fetus looks recognizably human. The face has defined features, the body is proportioned more like a newborn than the oversized-head shape of earlier months, and the skin is covered in a thin, translucent layer that reveals blood vessels underneath. From head to heel, the fetus measures roughly 25 to 27 centimeters (about 10 inches) and weighs around 300 to 450 grams, or just under a pound.
Size and Proportions
Think of something roughly the length of a banana. The head is still large relative to the body, but the limbs have caught up considerably compared to the first trimester, when the head made up nearly half the total length. Arms and legs are now long enough to bend and cross, and fingers and toes are fully separated with tiny, soft nails growing at the tips. The fetus can make a fist, and on ultrasound, it’s common to catch a thumb near or in the mouth.
Facial Features
By five months the face looks remarkably detailed. The ears have moved into their final position on the sides of the head, and the eyes, though still fused shut, can move slowly beneath the eyelids. Eyebrows are just beginning to appear as fine lines, and a layer of soft hair is growing on the scalp. Eyelashes come a bit later, typically forming closer to six months. The nose, upper lip, lower lip, and chin are distinct enough that an ultrasound technician can line them up in profile to check for normal alignment.
The eyes are spaced symmetrically, with the gap between the orbits roughly equal to the width of each eye socket. These proportions are one of many things checked during the mid-pregnancy anatomy scan.
Skin, Hair, and the Waxy Coating
The skin at five months is thin and somewhat wrinkled because the fetus hasn’t yet built up the layer of body fat that will fill it out in the third trimester. Blood vessels are visible through the skin, giving it a reddish or pinkish tone rather than the color it will have at birth.
Two protective layers now cover the body. The first is lanugo, a coat of soft, feathery hair that can range from very light to dark. It covers most of the body and serves a specific purpose: it helps anchor the second layer, a waxy, cheese-like coating called vernix. Together, lanugo and vernix insulate the fetus and protect delicate skin from the amniotic fluid, which would otherwise damage it over months of constant exposure. Lanugo also plays a surprising role in growth. As it moves in the fluid, it sends vibrations to sensory receptors in the skin, and those signals help stimulate the fetus’s overall development.
What the Fetus Can Do
Five months marks a busy period for movement. This is when most pregnant people feel “quickening” for the first time, typically between 16 and 20 weeks. It doesn’t feel like a kick yet. Women describe it as fluttering like a butterfly, tiny pulses, bubbles popping, or light rolls and tumbles. The sensation is usually felt low in the belly, near the pubic bone. First-time mothers sometimes mistake it for gas.
The fetus at this stage is doing more than just shifting position. It swallows amniotic fluid regularly, which helps the digestive system practice. It cycles between periods of sleep and wakefulness. On ultrasound, you might see it yawning, stretching, or bringing a hand to its face.
Hearing Begins
One of the more remarkable developments at five months is the start of hearing. Research has shown that fetuses respond to sound as early as 19 weeks, beginning with low-frequency tones. At this stage, they’re most sensitive to sounds around 500 Hz, which falls in the range of a speaking voice. Higher-pitched sounds won’t get a response for several more weeks. By 27 weeks, nearly all fetuses respond to low-frequency tones, but it takes until 33 to 35 weeks for them to react to higher frequencies. As the auditory system matures, the volume needed to produce a response drops by 20 to 30 decibels, meaning the fetus becomes dramatically more sensitive to sound over time. This early sensitivity to the pitch of human speech may actually help lay groundwork for language learning after birth.
Brain Development at Five Months
The brain is growing rapidly. The production of new brain cells, which began around week four, reaches its final stretch around week 20. The body actually produces far more brain cells during pregnancy than will exist in the adult brain and spinal cord. Many will be pruned away later as the brain refines its connections. At the same time, a different type of cell (the kind that supports and insulates nerve cells rather than transmitting signals) begins its own production around week 19, a process that continues after birth.
The corpus callosum, the thick band of fibers connecting the left and right halves of the brain, has already formed by this point. It began growing around week nine and fused into a single structure between weeks 13 and 14. By five months, the brain’s surface is still relatively smooth. The characteristic folds and grooves that dramatically increase surface area will develop mostly in the third trimester.
Lungs and the Road to Viability
At five months the lungs are in what’s called the canalicular stage of development, which runs from about 16 to 25 weeks. During this phase, the airways are branching and the cells that will eventually produce surfactant (a slippery substance that keeps air sacs from collapsing) are just beginning to appear. Around week 20, tiny storage structures for surfactant start forming inside lung cells. But meaningful surfactant production doesn’t begin until about 24 weeks, and adequate amounts to support breathing aren’t produced until around 32 weeks. This is a major reason why extreme prematurity is so dangerous.
Survival outside the womb at the tail end of the fifth month (22 to 23 weeks) is possible but depends heavily on the level of care available. In hospitals that provide aggressive intervention for extremely premature infants, survival rates at 22 weeks can reach 50%. At 23 weeks, those centers see survival rates around 65 to 67%. In facilities without that same level of specialized neonatal care, survival drops significantly. National surveys from Japan, Sweden, and the United States have all documented survival exceeding 50% at 22 weeks in centers that actively treat these infants.
What You See on the Anatomy Scan
The mid-pregnancy ultrasound, usually done around 18 to 22 weeks, is the most detailed look at the fetus you’ll get during pregnancy. The technician measures four key dimensions: the width of the head, the circumference of the head, the circumference of the abdomen, and the length of the thighbone. Together, these measurements track growth and help confirm gestational age.
Beyond measurements, the scan is a systematic review of anatomy. The technician checks that the heart is positioned on the left side of the chest, examines its four chambers and outflow tracts, and looks at blood flow through the major vessels. They image the brain in multiple planes, measure the fluid-filled spaces inside it, and check the cerebellum at the back of the skull. Both kidneys are viewed from two angles. The stomach is confirmed to be on the left side. The spine is traced for completeness, and the umbilical cord insertion into the abdomen is inspected for any wall defects.
For parents, this is often the scan where the fetus first looks like a baby on screen. You can see the profile of the face, watch the heart beating in its four chambers, and sometimes catch the fetus mid-movement. If the position is right, sex can typically be identified at this stage as well.