At six months of pregnancy, a fetus is roughly the size of an ear of corn, measuring about 8.25 inches from crown to rump and weighing just over 1.3 pounds. This stage falls around weeks 24 to 27 of pregnancy, near the end of the second trimester, and it’s a period of dramatic visible change. The fetus now looks unmistakably human, with defined facial features, visible fingernails, and skin that’s gaining color and texture week by week.
Overall Size and Proportions
At this point, the body proportions are starting to look more like a newborn’s. Earlier in pregnancy, the head made up a disproportionately large share of the body, but by six months the limbs have lengthened and the torso has filled out enough that the overall shape is more balanced. The legs are drawn up in the classic fetal position, tucked against the chest inside the limited space of the uterus. The fetus weighs about 630 grams, or roughly 1.3 pounds, and while that’s still very small, it’s a significant jump from just a few weeks earlier. Weight gain accelerates from here as the fetus starts putting on layers of fat beneath the skin.
Skin, Hair, and Surface Details
The skin at six months is still thin and somewhat translucent, with blood vessels visible beneath the surface. It has a reddish or pinkish tone because there isn’t much fat underneath yet to obscure the blood supply. Wrinkles are prominent for the same reason: there’s more skin than fat to fill it out.
Two distinctive coverings protect this delicate skin. The first is lanugo, a soft, fine hair that developed between weeks 16 and 20 and now covers much of the body. Lanugo serves as an anchor for the second layer: vernix caseosa, a waxy, white coating that clings to the hair and acts as a waterproof barrier. Without this combination, the amniotic fluid surrounding the fetus would irritate and damage the skin. Together, they also help insulate the body and regulate temperature. Most of the lanugo will shed before birth, though some babies are born with patches of it still visible.
Fingerprints are already fully established by this stage. The ridge patterns on the fingertips form between weeks 13 and 17, so by six months, each finger and toe carries a unique print that will remain unchanged for life.
Facial Features
The face at six months is recognizably human and increasingly expressive. Eyebrows and eyelashes have grown in, and the eyelids, which were fused shut for most of earlier development, are beginning to open. The eyes can now detect changes in light filtering through the uterine wall, though full vision won’t develop until well after birth. The nose, lips, and chin are well defined. On ultrasound, many parents can clearly make out their baby’s profile at this stage, and some notice the fetus opening and closing its mouth or even appearing to yawn.
Movement and Reflexes
Six months is when fetal movement becomes a regular, noticeable part of daily life for the pregnant person. Earlier movements may have felt like gentle flutters or bubbles, but by now the kicks, rolls, jabs, and stretches are distinct enough to be felt clearly. Some people describe them as swishes or butterflies, while others feel definite punches. The fetus is still small enough to have room to shift positions, so you might feel activity in different areas of your abdomen throughout the day.
The fetus also hiccups regularly, which feels like a small, rhythmic tapping. These hiccups are a byproduct of the fetus practicing breathing motions, drawing amniotic fluid in and out of developing lungs. Startle reflexes are present too: a loud noise or sudden movement can trigger a visible jolt. That said, movements at this stage are still lighter than what comes in the third trimester, when kicks grow noticeably stronger.
Hearing and Sensory Development
By 24 weeks, the ears are rapidly maturing, and the fetus can hear sounds from inside the body: the rhythmic beat of the heart, air flowing through the lungs, the gurgling of digestion, and blood pulsing through the umbilical cord. These internal sounds form a constant backdrop. By around weeks 25 or 26, research shows that fetuses begin responding to external sounds as well, particularly voices. Studies have demonstrated that babies at this stage react to noise with changes in heart rate or movement, suggesting real auditory processing is underway.
Brain Development at Six Months
The brain is in a period of explosive growth. By 24 to 26 weeks, the nervous system has matured enough to begin regulating complex functions like heart rate and body temperature on its own, which is a major milestone. The surface of the brain, which was relatively smooth earlier, is starting to develop the folds and grooves that dramatically increase its surface area. The outer layer responsible for voluntary movement, memory, and awareness is becoming more active, though it won’t reach full function until the final weeks of pregnancy and well into infancy.
This rapid brain development is one reason the third trimester is so critical. While the basic wiring is in place by six months, the connections between brain cells are still multiplying and strengthening, a process that will continue for years after birth.
Lung and Organ Development
The lungs are one of the last major organs to mature. At six months, the basic structure is in place and the fetus practices “breathing” by inhaling and exhaling amniotic fluid, but the lungs cannot yet function in open air. A key substance that keeps the tiny air sacs in the lungs from collapsing doesn’t begin production until around 26 weeks, and adequate levels aren’t reached until closer to 35 weeks. This is the primary reason very premature babies often need breathing support.
Other organs are further along. The heart has been beating since early in the first trimester and now pumps blood efficiently through a growing circulatory system. The digestive tract is functional enough to absorb small amounts of nutrients from swallowed amniotic fluid. The kidneys are producing urine, which actually contributes to the amniotic fluid surrounding the fetus.
Bones and Muscles
The skeleton at six months is transitioning from soft cartilage to harder bone. This process, called ossification, has been underway for some time, but specific bones are reaching key hardening milestones right around the sixth month. The heel bone and the ankle bone both begin solidifying their primary centers during this period, and the small bones of the fingers and toes are progressing through their own hardening process. The skeleton is still flexible enough to accommodate the cramped fetal position, but it’s becoming increasingly sturdy. Muscles have developed enough to power the kicks and movements felt through the abdominal wall, and they’ll continue to strengthen throughout the rest of pregnancy.
Viability Outside the Womb
Six months marks a significant threshold: this is roughly when a fetus first becomes potentially viable outside the womb with intensive medical support. Survival rates at 24 weeks range from about 42% to 59%, according to the American College of Obstetricians and Gynecologists. By 25 weeks, that rate climbs to 67% to 76%. These numbers reflect modern neonatal intensive care, and outcomes vary widely depending on the individual circumstances, birth weight, and the hospital’s resources.
Babies born this early face serious health challenges, particularly with breathing, temperature regulation, and feeding. The fact that viability begins at this stage speaks to how far organ development has come by six months, but it also highlights how much growth and maturation still needs to happen in the final trimester. A fetus at six months is recognizable, responsive, and increasingly complex, but still in the middle of critical development that will continue for the remaining 14 or so weeks of pregnancy.