At 4 months of pregnancy (roughly weeks 14 through 17), your baby is about the size of a pear. That translates to roughly 4 to 5 inches long from crown to rump and around 4 to 5 ounces in weight. This is the stage when growth starts accelerating quickly, and your baby begins looking less like a tiny cluster of cells and more like a recognizable human.
Week-by-Week Size During Month 4
Because a month of pregnancy spans several weeks, your baby’s size changes noticeably from the start of month 4 to the end. At week 14, the baby measures about 3.5 inches and weighs roughly 1.5 ounces. By week 17, length reaches closer to 5 inches and weight doubles or triples to around 5 ounces. The body is finally catching up to the head, which dominated proportions during the first trimester.
During these weeks, your baby’s skeleton begins hardening from soft cartilage into bone. Tiny fingerprints form on the fingertips, and a fine layer of hair called lanugo covers the skin to help regulate temperature. The eyes shift from the sides of the head toward the front of the face, and the ears move into their final position. If you have an ultrasound during this period, you may be able to see your baby sucking a thumb or making facial expressions.
What Your Baby Can Do at This Stage
Month 4 is when movement really picks up. Your baby is stretching, kicking, and flexing arms and legs inside the amniotic fluid. Many of these movements are still too small for you to feel, especially in a first pregnancy, but they’re happening constantly. The nervous system is developing rapidly, and your baby is practicing swallowing amniotic fluid, which helps the digestive system mature.
By the end of this month, the reproductive organs are developed enough that an ultrasound technician can sometimes identify the sex, though positioning doesn’t always cooperate. The kidneys are functional and producing small amounts of urine, which becomes part of the amniotic fluid.
How Your Body Changes at 4 Months
This is typically when the pregnancy becomes visible to others. Your uterus has grown to about the size of a small melon and sits just below your belly button. Many people notice their regular clothes getting tight around the waist during this period, and the characteristic bump starts to show.
The good news: for most people, the nausea and fatigue of the first trimester fade during month 4 as you enter the second trimester. Energy levels often rebound, and appetite returns. Some people experience a noticeable increase in hunger, which makes sense given how rapidly the baby is growing. Round ligament pain, a sharp or aching sensation on the sides of your lower belly, is common as the uterus expands and the ligaments supporting it stretch.
What Supports Healthy Growth
Your baby’s rapid bone development during month 4 means your calcium and vitamin D intake matters more than ever. Iron needs also increase as your blood volume expands to support the placenta. Most prenatal vitamins cover these bases, but eating iron-rich foods like leafy greens, beans, and lean meats helps your body absorb what it needs more efficiently.
Caloric needs increase by about 300 to 350 extra calories per day during the second trimester. That’s roughly the equivalent of a handful of nuts and a piece of fruit, not the “eating for two” many people imagine. Staying hydrated supports the increasing amniotic fluid volume your baby relies on for cushioning and movement practice.
When Growth Feels Different Than Expected
Belly size at 4 months varies enormously from person to person. Factors like your height, torso length, abdominal muscle tone, and whether this is your first pregnancy all influence how big you look. Someone carrying their second baby often shows earlier because the abdominal muscles are already stretched from the previous pregnancy. A taller person with a long torso may barely show at all.
Your provider tracks growth by measuring fundal height (the distance from your pubic bone to the top of the uterus) starting around 20 weeks, and through ultrasound measurements when needed. A belly that looks smaller or larger than someone else’s at the same stage rarely signals a problem. The baby’s actual measurements on ultrasound are what matter, not how your bump compares to photos online.