At 25 weeks, a baby is about 13¼ inches long from head to heel and weighs roughly 1¾ pounds, comparable in size to an acorn squash. The body is recognizably human but visibly unfinished: the skin is wrinkled, thin enough to see blood vessels through, and covered in fine hair and a waxy coating. Whether you’re picturing your baby on an ultrasound or preparing for a premature birth, here’s what a 25-week baby actually looks like and what’s happening under the surface.
Skin, Hair, and Body Proportions
The most striking feature of a 25-week baby is the skin. It’s still translucent and deeply wrinkled, almost like tissue paper draped over a tiny frame. That see-through quality exists because the baby hasn’t yet built up much subcutaneous fat. Fat deposits really start filling in closer to 27 weeks, which is when the skin begins to look smoother and more opaque. At 25 weeks, you can often see a network of blood vessels just beneath the surface.
Covering nearly all of the skin is a layer of fine, downy hair called lanugo. This soft fuzz starts growing around 21 weeks and serves a practical purpose: it helps anchor a thick, greasy coating called vernix caseosa to the skin. Vernix, which begins forming around 19 weeks, protects the baby’s delicate skin from the amniotic fluid. Together, the lanugo and vernix give the baby a slightly fuzzy, cheese-coated appearance that can surprise parents seeing their baby for the first time, whether on a detailed ultrasound or after an early delivery.
The head is still large relative to the body, and the limbs are thin. Fingers and toes are fully formed with tiny nails. The baby’s arms and legs look long and spindly because there’s so little fat padding them out.
Facial Features and Eyes
By 25 weeks, the face looks remarkably like a newborn’s. The nose, lips, and ears are well-shaped, and eyebrows and eyelashes are present. The eyelids, which fused shut early in pregnancy to protect the developing eyes, are just about to open. Most babies begin opening their eyelids right around 26 weeks, so at 25 weeks those eyes are on the verge of seeing for the first time.
Even before the lids open, the eyes are responding to the outside world. Research using light projected through the uterine wall has shown that fetuses orient their heads toward light patterns, particularly face-like shapes, starting around 26 weeks. The visual system is wiring up rapidly during this period as connections between the eyes and the brain’s processing centers form.
What the Baby Can Hear and Feel
A 25-week baby is far from a passive passenger. The hearing system has been developing for weeks, and by this point the baby responds to a range of sounds. Fetuses first react to tones around 500 Hz (roughly the pitch of a normal speaking voice) as early as 19 weeks. By 25 weeks, they consistently respond to low-frequency sounds like deep voices and music, though higher-pitched sounds above 1,000 Hz won’t reliably trigger a response until later. These responses show up as sudden movements when researchers place a speaker against the mother’s abdomen.
The baby also has a developing startle reflex. When exposed to a sudden sound or vibration, the whole body reacts with a quick, generalized jolt. This reflex becomes more reliable and consistent after 30 weeks, but the neural wiring that drives it is already active at 25 weeks. Parents often notice strong kicks or shifts in response to loud noises, a door slamming, or a sudden burst of music.
Movement Patterns
At 25 weeks, most mothers feel their baby moving regularly. The baby cycles between periods of sleep and wakefulness, and during active phases you can expect rolling, stretching, kicking, and even hiccupping. The movements feel more deliberate and forceful than the flutters of earlier weeks because the baby is bigger and stronger, though there’s still enough room in the uterus for full somersaults. Many babies haven’t settled into a head-down position yet and may flip between breech and vertex several times a day.
What’s Developing Inside
The most critical development happening at 25 weeks is invisible: the lungs. At this stage, the lungs are structurally immature and only beginning to produce surfactant, a slippery substance that coats the air sacs and keeps them from collapsing with each breath. Without enough surfactant, a baby can’t exchange oxygen efficiently. This is the single biggest challenge for babies born at this age and the reason lung support is the centerpiece of their medical care.
The brain is also in a period of explosive growth. The surface, which was relatively smooth, is starting to develop the folds and grooves that characterize a mature brain. Billions of nerve connections are forming, supporting the baby’s increasing ability to process sound, respond to touch, and regulate basic body functions. The nervous system is functional enough to coordinate breathing-like movements (the baby “practices” inhaling and exhaling amniotic fluid) but not yet mature enough to reliably manage breathing, temperature, or feeding outside the womb.
If a Baby Is Born at 25 Weeks
A baby born at 25 weeks is considered extremely premature. In person, these babies look strikingly small and fragile. Their skin is reddish or purplish and almost gelatinous, their eyes may be fused or just beginning to open, and their entire body can fit roughly in an adult’s two hands. Most weigh less than 2 pounds.
Survival rates at 25 weeks range from 59% to 86%, depending on the hospital, the baby’s weight, and other health factors. That wide range reflects real differences in access to specialized neonatal care. In hospitals with advanced NICUs, outcomes tend to cluster toward the higher end.
Babies born this early need significant medical support. They’re placed in enclosed incubators that regulate temperature and humidity, since they lack the body fat to stay warm on their own. Continuous monitors track breathing and heart rate around the clock. Nearly all 25-week babies need help breathing, ranging from supplemental oxygen to a ventilator, because their lungs don’t produce enough surfactant yet. Surfactant can be given as a medication directly into the lungs, which significantly improves breathing function.
Feeding is another challenge. The suck-swallow-breathe coordination needed for nursing or bottle-feeding doesn’t develop until closer to 34 weeks, so 25-week babies receive nutrition through a vein or through a tiny tube threaded into the stomach. Other common interventions include eye exams to watch for abnormal blood vessel growth in the retina, monitoring for a heart condition where a fetal blood vessel doesn’t close on its own after birth, and antibiotics if infection is a concern.
NICU stays for 25-week babies typically last until close to the original due date, often three months or more. The journey is gradual: babies slowly transition from ventilator support to breathing on their own, from IV nutrition to tube feeding to oral feeding, and from the incubator to an open crib as they gain weight and learn to regulate their own temperature.