At 24 weeks of pregnancy, a baby weighs roughly 1⅓ pounds (630 grams) and measures about 8¼ inches (210 millimeters) from crown to rump. That’s approximately the size of an ear of corn. This week marks a significant milestone in pregnancy: it’s widely considered the threshold of viability, meaning a baby born at this stage has a meaningful chance of survival with intensive medical care.
What’s Developing at 24 Weeks
By week 24, the baby’s skin is wrinkled, translucent, and tinted pink or red from blood flowing through visible vessels beneath the surface. The lungs have begun producing surfactant, a substance that helps the tiny air sacs inflate properly and prevents them from collapsing. This is one of the most critical developments in the second trimester, because functional lungs are the biggest barrier to survival outside the womb.
Fingerprints and footprints are forming from ridges on the palms and soles. The baby has started making rapid eye movements. The brain is growing quickly, and the inner ear is developed enough that the baby can respond to sound. Fat stores are still minimal at this point, which is why the skin appears wrinkled: there’s not yet enough body fat to fill it out. Over the coming weeks, the baby will gain weight rapidly as fat deposits build.
Why Some Babies Measure Larger or Smaller
The 630-gram average is just that: an average. Individual babies can weigh noticeably more or less at this stage, and several factors explain the variation. Genetics play a direct role. Research published in Scientific Reports identified multiple genetic variants that influence how fast a fetus grows, with some acting specifically during the 20-to-25-week window. In other words, some of the size difference between babies at 24 weeks is hardwired.
Maternal health matters too. Babies of mothers with obesity tend to measure larger on ultrasound as early as 21 weeks. Conditions like preeclampsia or placental insufficiency can restrict blood flow and nutrients, leading to smaller measurements. Carrying multiples also means each baby typically weighs less individually than a singleton at the same gestational age. If your provider flags a measurement that’s above or below average, they’ll usually follow up with additional ultrasounds to track the growth trend rather than relying on a single reading.
Why 24 Weeks Is Considered Viable
Week 24 is a turning point because survival rates rise sharply around this stage. Data from the American Academy of Pediatrics covering 2020 to 2022 shows that 71.1% of all babies born at 24 weeks survived to hospital discharge. That’s a substantial jump from 52.8% at 23 weeks and 24.9% at 22 weeks.
Survival, however, doesn’t tell the whole story. Among babies born at 24 weeks who received life support, only about 26% survived without severe complications. The median hospital stay for survivors was 127 days, or roughly four months. At discharge, about 58% still needed supplemental oxygen and around 57% went home on a monitor. These numbers reflect just how early 24 weeks still is in development, even though the odds of survival are now better than ever.
Because of this viability threshold, medical teams generally shift their approach around this gestational age. If preterm labor threatens at 24 weeks, hospitals with neonatal intensive care units will typically offer interventions aimed at delaying delivery and supporting the baby’s lung development. Care decisions are individualized based on the specific circumstances rather than following a rigid cutoff.
What You Might Be Feeling at 24 Weeks
Your uterus is now large enough to push against your ribs, back, and stomach, which can cause aches in places you didn’t expect. Round ligament pains, those sharp twinges along the sides of your belly, are common as the uterus stretches. Pregnancy hormones are loosening your ligaments and muscles throughout your body, contributing to backaches, leg cramps, and general soreness.
Other typical symptoms at this stage include heartburn, constipation, swollen hands and feet, stretch marks, and feeling overheated. Some women notice their skin darkening on the face, sometimes called the “mask of pregnancy.” You might still be dealing with earlier symptoms like morning sickness, food cravings, or a heightened sense of smell, though for many women these ease during the second trimester. Sleep can become harder to come by as finding a comfortable position gets more difficult and trips to the bathroom become more frequent.
How Baby’s Weight Changes From Here
At 24 weeks, your baby is roughly a third of the way to the average full-term birth weight of about 7.5 pounds. The third trimester is when the most dramatic weight gain happens. Between now and delivery, the baby will gain approximately 6 pounds, putting on fat that smooths out wrinkled skin, regulates body temperature, and provides energy reserves for the first days after birth. By 28 weeks most babies weigh around 2.2 pounds, by 32 weeks about 3.75 pounds, and by 36 weeks roughly 5.75 pounds. Growth in these final months is rapid and heavily influenced by nutrition, placental function, and the same genetic factors already shaping your baby’s size.