At 24 weeks, a fetus measures about 12.5 inches (roughly 32 centimeters) from head to heel and weighs close to 1.5 pounds (around 630 grams). That’s about the length of an ear of corn. While those numbers give you the basics, 24 weeks is a significant milestone in development, with major changes happening in the lungs, brain, and skin.
Length, Weight, and How Size Is Measured
Fetal measurements can be confusing because they’re reported two different ways. The “crown-to-rump” length, which measures from the top of the head to the bottom of the tailbone, is about 8.25 inches (210 millimeters) at 24 weeks. The full head-to-heel length, which includes the legs, comes to roughly 12.5 inches. Most ultrasound measurements use the crown-to-rump figure, while pregnancy apps and week-by-week guides tend to give the full length.
Weight at this stage is a little over 1.3 pounds, though healthy fetuses can fall somewhat above or below that number. Growth isn’t perfectly uniform. Some weeks the baby gains more length, other weeks more weight. From here on, weight gain accelerates considerably as the fetus starts building fat stores under the skin.
What the Baby Looks Like
At 24 weeks, the fetus is still quite lean. There’s very little body fat yet, so the skin appears wrinkled and somewhat translucent, with blood vessels visible beneath the surface. A fine layer of soft hair called lanugo covers the body. This hair serves an important purpose: it holds a waxy, protective coating called vernix in place on the skin. Without that coating, the amniotic fluid could irritate and damage the fetus’s delicate skin. Over the coming weeks, the baby will fill out as fat deposits build up, and most of the lanugo will shed before birth.
Facial features are well formed by now. The eyes have developed, though the irises don’t yet have pigment. Fingerprints and footprints are in place. The ears are fully shaped and positioned on the sides of the head.
Lung Development Begins a Critical Phase
The lungs hit a key turning point around 24 weeks. This is when specialized cells in the lungs begin producing surfactant, a slippery substance that keeps the tiny air sacs from collapsing when a baby breathes. Without surfactant, the lungs can’t exchange oxygen effectively. The lungs are still far from mature at this point. They won’t be fully ready for breathing on their own until closer to 36 weeks. But the fact that surfactant production starts now is one reason 24 weeks is considered the threshold of viability.
Brain and Sensory Development
The brain is growing rapidly during this period. At 24 weeks, the connections between the brain’s deeper relay centers and the outer cortex are forming, laying the groundwork for processing sensory information. These early circuits are the foundation for everything from responding to sound to regulating body temperature after birth.
Hearing is one of the first senses to come online. By 24 weeks, the inner ear structures are developed enough that the fetus responds to sounds. Loud noises may cause a startle reflex, and the baby can begin to recognize recurring sounds like a parent’s voice or a heartbeat. Many parents notice that the baby reacts to music or sudden loud sounds around this time.
Movement Patterns at 24 Weeks
If you’re 24 weeks pregnant, you’ve likely been feeling movement for several weeks already. What started as gentle flutters has probably become more defined. Kicks, rolls, and jerky movements are all normal at this stage. The baby still has enough room to change positions frequently, so you might feel activity in different spots from day to day.
There’s no set number of movements you should feel each day, since every baby has a different activity level. What matters more than counting kicks at this stage is starting to get familiar with your baby’s general pattern of movement: the times of day when activity picks up and the periods when things are quiet. The baby does cycle between periods of sleep and wakefulness, though these don’t align neatly with your own sleep schedule.
Why 24 Weeks Is a Viability Milestone
If a baby is born at 24 weeks, survival is possible but comes with serious challenges. A large study published in Pediatrics, drawing from data on nearly 7,000 infants born at 24 weeks between 2020 and 2022, found that about 71.5% of those who received active medical support survived to leave the hospital. That’s a meaningful jump from 23 weeks, where survival drops to roughly 53%.
Survival alone doesn’t capture the full picture, though. Among the 24-week survivors in that study, about 26% made it through without severe complications. More than half went home needing supplemental oxygen, and over half were discharged with a monitor. The median hospital stay was 127 days, or a little over four months. These numbers reflect how much growing and developing a 24-week baby still needs to do outside the womb.
Every additional week of pregnancy at this stage makes a substantial difference. At 25 weeks, survival rises to about 82%, and the rate of complication-free survival nearly doubles compared to 24 weeks.
What You Might Notice in Your Own Body
Your uterus has grown enough that your healthcare provider can now measure it from the outside. This measurement, taken from the pubic bone to the top of the uterus, is called the fundal height. At 24 weeks, it should be roughly 24 centimeters, give or take 2 centimeters. This quick check at prenatal visits helps confirm that the baby’s growth is on track without needing an ultrasound every time.
The top of the uterus is now at about the level of your belly button. You may be noticing more pressure on your lower back and bladder as the baby gets bigger, and round ligament pain (sharp twinges on the sides of your belly when you move suddenly) is common at this stage. Weight gain typically picks up from here, as the baby enters its fastest growth phase.