At 25 weeks, a fetus measures about 13.6 inches (34.6 cm) from head to rump and weighs roughly 1.5 pounds (660 grams), about the size of a rutabaga. That’s big enough to fill most of your hand and heavy enough that you’re almost certainly feeling regular movement by now.
Length, Weight, and Normal Variation
The average 25-week fetus is just under 14 inches long and about a pound and a half. But “average” covers a wide range. Canadian population data on birth weight at 25 weeks shows that boys at the 10th percentile weigh around 617 grams (1.36 lbs), while boys at the 90th percentile reach 981 grams (2.16 lbs). Girls run slightly smaller, ranging from about 578 grams at the 10th percentile to 918 grams at the 90th. All of those weights fall within normal bounds. Your provider tracks growth over multiple ultrasounds rather than relying on a single measurement, so one reading above or below the average isn’t cause for concern on its own.
What’s Developing Right Now
Week 25 sits at an important stretch of the second-to-third trimester transition, when several systems are maturing quickly. The fetus is adding body fat, which fills out previously wrinkled skin and gives it a plumper appearance. The nervous system is rapidly maturing as well, laying groundwork for the sensory abilities that come online over the next few weeks.
By around week 26, the lungs begin producing surfactant, a slippery substance that keeps the tiny air sacs from collapsing and is essential for breathing outside the womb. And by week 27, the eyelids can open and blink for the first time. These milestones cluster together because the body is preparing, in broad strokes, for the possibility of life outside the uterus even though full term is still 15 weeks away.
Senses at 25 Weeks
The fetus can already detect both sound and light at this stage, though responses are still developing. Research on fetal reactions to light stimulation found that about 30% of fetuses responded to a bright flash as early as 23 weeks, with that proportion climbing steadily toward 77% by full term. So at 25 weeks, your baby likely has some ability to perceive light filtering through the uterine wall, though the response isn’t yet consistent.
Hearing is on a similar trajectory. Fetuses at 28 weeks respond to louder sounds with noticeable movement and heart rate changes, and that sensitivity sharpens as the weeks pass. At 25 weeks, the auditory system is functional enough that the fetus is regularly exposed to your heartbeat, digestion, and voice, all of which travel easily through amniotic fluid. Many parents notice that loud noises produce a startle or kick around this time.
What Movement Feels Like
Most people start feeling fetal movement around 20 weeks, and by 25 weeks those sensations are more distinct. Early kicks often feel like flutters, swishes, or rolling motions. As the fetus grows and gains muscle strength, movements shift toward sharper jabs and more recognizable kicks. Ten movements (kicks, flutters, or rolls) within a two-hour window is the general benchmark used to assess healthy activity. You don’t need to start formal kick counting just yet if your provider hasn’t asked you to, but paying casual attention to your baby’s active periods helps you learn their patterns.
What Happens if a Baby Is Born at 25 Weeks
A baby born at 25 weeks is extremely premature but has a meaningful chance of survival with intensive care. Data from the American Academy of Pediatrics covering 2020 to 2022 found that 82% of infants born at 25 weeks who received postnatal life support survived to hospital discharge. That’s a significant jump from 71% at 24 weeks and 53% at 23 weeks, illustrating how much each additional week of development matters at this stage.
Survival, however, doesn’t tell the whole story. Among 25-week survivors, about 43% were discharged without severe complications. At the time of discharge, roughly 45% of these babies still needed supplemental oxygen or a monitor, and about 6% required a feeding tube. The median hospital stay for a 25-week survivor was 110 days, or just under four months. These numbers reflect how much growth and development still needs to happen after such an early birth, and why every additional week in the womb makes a measurable difference in outcomes.
How Size Changes From Here
The third trimester is when the fetus gains weight most dramatically. At 25 weeks, your baby is roughly 1.5 pounds. By 28 weeks, that typically doubles to around 2.5 pounds. By 32 weeks, most fetuses weigh close to 4 pounds, and by 36 weeks, about 6 pounds. Much of this gain is body fat, which the baby needs for temperature regulation and energy after birth. The rapid weight gain also means your belly will grow noticeably over the next several weeks, and you may find that movements feel stronger and more cramped as the fetus runs out of room to somersault freely.