At 24 weeks, a fetus is about 12.7 inches (32 cm) long and weighs roughly 1.5 pounds (670 grams), comparable in length to an ear of corn. It looks unmistakably human at this point, with defined facial features, visible hair, and limbs that move with increasing coordination. This is also the gestational age widely considered the threshold of viability, meaning survival outside the womb becomes possible with intensive medical care.
Size and Proportions
The 24-week fetus is lean. Nearly all of its length comes from a body that hasn’t yet accumulated the fat stores that fill out a full-term baby’s cheeks and limbs. The head is still large relative to the body, roughly one-third of the total length, though the rest of the body is catching up. Arms and legs are thin and bony-looking, with joints that flex and extend freely. Over the coming weeks, the fetus will gain fat rapidly, but at 24 weeks it still has a wiry, angular appearance.
Skin, Hair, and Protective Coatings
The skin at 24 weeks is thin enough to be somewhat translucent, with blood vessels visible beneath the surface. It appears reddish or dark pink because there’s very little subcutaneous fat to obscure the underlying tissue. Two features protect this delicate skin. The first is lanugo, a fine, downy hair that covers much of the body and helps regulate temperature. The second is vernix caseosa, a thick, waxy, white coating that shields the skin from the amniotic fluid surrounding the fetus. Both are temporary. Lanugo typically sheds before birth in full-term babies, and vernix thins out during the final weeks of pregnancy.
Facial Features
By 24 weeks, the face has all its major features in place. Eyebrows are visible, and eyelashes are forming. The eyelids, which were fused shut for months, are beginning to separate. Full eye-opening typically happens closer to 26 weeks, but the process starts now. The nose, lips, and ears are well-shaped and proportional. The ears in particular have moved to their final position on the sides of the head, a shift that happened gradually over the second trimester.
The eyes themselves are developed structurally, though the irises don’t yet have their final pigment. Most fetuses at this stage have eyes that would appear dark or bluish if seen directly, regardless of their eventual eye color.
Hands, Feet, and Fingerprints
The fingers and toes are fully separated with soft, tiny nails growing on each one. The nails haven’t yet reached the fingertips but are clearly present. One of the more remarkable details: unique fingerprints and footprints have already formed. These patterns developed weeks earlier and are now permanent. The hands grasp reflexively, and the fetus frequently brings its fingers to its face or grips the umbilical cord.
Brain Development
The brain at 24 weeks is in a period of rapid change. Its surface is still relatively smooth compared to a full-term brain, which is covered in the characteristic folds and grooves that dramatically increase surface area. Those folds, called gyri and sulci, are just beginning to form at 24 weeks. A critical layer of the brain called the subplate is prominent at this stage, acting as a temporary relay station where early neural connections are organized before the cortex matures enough to take over. Over the next 16 weeks, the brain’s surface will transform from mostly smooth to deeply wrinkled, and the subplate will gradually shrink as permanent wiring takes its place.
This brain development is directly tied to the fetus’s increasing ability to process information. Sleep cycles are emerging, with the fetus alternating between periods of activity and rest. Much of its sleep time is spent in rapid eye movement (REM) sleep, during which the eyes move beneath the still-closed lids. REM sleep is thought to play a role in brain maturation.
Hearing and Sensory Responses
The inner ear is structurally developed by 20 weeks, but 24 weeks is when the fetus starts actively responding to sound. External noises are muffled inside the womb but not silenced. The fetus can hear voices, music, and loud environmental sounds. Researchers have documented changes in heart rate and movement in response to sudden noises at this age. The mother’s voice, transmitted partly through her own body, is the most prominent sound the fetus hears. Very loud or prolonged noise exposure can potentially affect the developing auditory system, which is one reason occupational noise guidelines exist for pregnant workers.
Movement Patterns
If you’re 24 weeks pregnant, you’ve almost certainly been feeling movement for several weeks. What started as faint flutters, often described as bubbles popping or tiny muscle spasms, has grown stronger and more defined. At 24 weeks, you can expect kicks, rolls, and occasional sharp jabs as the fetus stretches and repositions itself. There’s still enough room in the uterus for full somersaults.
You may also start noticing patterns. The fetus tends to be less active during the day, partly because your own movement rocks it to sleep. Nighttime or periods when you’re lying still often bring the most noticeable activity. These aren’t random bursts. The fetus is developing a genuine sleep-wake cycle, with distinct periods of rest and alertness that become more predictable over time. Occasionally you might feel tiny, rhythmic movements. Those are hiccups, caused by the diaphragm contracting as the fetus practices breathing motions.
Lung Development
The lungs are one of the last major organs to mature, and at 24 weeks they’re entering what’s known as the saccular stage. This is when the air sacs that will eventually handle gas exchange begin forming. Critically, the lungs start producing surfactant at 24 weeks. Surfactant is a slippery substance that keeps the air sacs from collapsing each time a person exhales. Without enough of it, breathing is extremely difficult.
At 24 weeks, surfactant production has just begun, and the quantity is far from sufficient for independent breathing. Adequate surfactant levels typically aren’t reached until around 32 weeks. This gap is a major reason premature infants born at 24 weeks need respiratory support, and why survival improves so dramatically with each additional week in the womb.
Survival Outside the Womb
Twenty-four weeks is a significant milestone in terms of viability. Based on a national database of nearly 50,000 infants born at completed 24 weeks of gestation, approximately 72% survived. That rate has improved over time, rising from about 68% in 2007 to over 73% by 2018 as neonatal care has advanced. For context, survival for infants born before 24 weeks drops sharply to around 24%.
Survival at 24 weeks, however, typically requires months of intensive hospital care. The lungs, brain, digestive system, and immune system are all still immature. Babies born at this stage face significant risks of long-term complications, and outcomes vary widely depending on birth weight, overall health, and the level of care available. Each additional week of gestation meaningfully improves both survival rates and long-term health outcomes.