At 18 weeks pregnant, your baby measures about 5.6 inches long and weighs roughly 6.7 ounces, or about 190 grams. That’s approximately the length of a cucumber. While still small enough to fit in the palm of your hand, your baby has grown dramatically from just weeks earlier and is now developed enough that you may start to feel movement for the first time.
Size and Weight at 18 Weeks
The 5.6-inch measurement refers to the length from the top of the head to the rump, not including the legs. This is how fetal length is typically measured in the first half of pregnancy because the legs are curled up tightly. If you were to stretch the baby out fully, the total length would be closer to 8 inches.
At 6.7 ounces, your baby weighs a little less than half a pound. To put that in perspective, that’s about the weight of a large chicken breast. Growth accelerates significantly from here. Over the next four weeks alone, your baby will nearly double in weight.
What’s Developing Right Now
Eighteen weeks is a busy time for brain development. The brain is producing nerve cells at its maximum rate right around weeks 17 and 18, and those cells are actively migrating to their final positions in the developing brain. This migration, which takes place mostly between weeks 12 and 20, is what builds the layered structure of the brain’s outer surface. The protective coating around nerve fibers that speeds up brain signals doesn’t develop until much later, mostly after birth, but the foundational wiring is being laid down now.
Your baby’s ears have developed enough to detect sound. This is one of the first senses to come online. The digestive system is also functional at this stage, processing the amniotic fluid that the baby swallows regularly. Meanwhile, the heart is fully formed and pumping about 25 quarts of blood per day, a volume that will continue to increase as the baby grows.
Feeling Your Baby Move
Eighteen weeks falls right in the window when many women first feel their baby move, a sensation called quickening. This typically happens between 16 and 20 weeks, though the timing varies. If you’ve been pregnant before, you’re more likely to recognize the feeling earlier, sometimes by 16 weeks. First-time mothers often don’t notice movement until closer to 20 weeks, partly because they’re not yet familiar with what it feels like.
Don’t expect kicks at this stage. The sensations are much subtler. Women commonly describe them as fluttering like a butterfly, tiny bubbles popping, light tapping, or small muscle spasms. These early movements are easy to mistake for gas or digestion, which is why many women aren’t sure what they felt until the movements become stronger and more regular over the following weeks. If you haven’t felt anything yet at 18 weeks, that’s completely normal.
The Anatomy Scan
Sometime between 18 and 22 weeks, you’ll likely be scheduled for a detailed ultrasound commonly called the anatomy scan. This is the most thorough ultrasound of the entire pregnancy, and it’s the one where many parents learn the baby’s sex if they choose to.
The scan goes well beyond a simple size check. A sonographer takes pictures and measurements of your baby’s heart, brain, spine, kidneys, bladder, arms, legs, hands, feet, lips, face, chest, lungs, stomach, and intestines. They also record the heart rate, check blood flow through the umbilical cord, evaluate where the placenta is positioned, and measure the amount of amniotic fluid surrounding the baby. On your side, they’ll look at your uterus, ovaries, and cervix.
The appointment typically takes 30 to 60 minutes, sometimes longer if the baby is in a position that makes certain views difficult. You may be asked to shift positions or walk around to encourage the baby to move. The purpose of this scan is to confirm that all major structures are developing normally and to flag anything that might need closer monitoring.
What Changes to Expect in Your Body
At 18 weeks, your uterus is roughly the size of a cantaloupe and sits just below your belly button. Most women are visibly showing by now, though the size of your bump depends on factors like your build, muscle tone, and whether this is your first pregnancy. You may notice your center of gravity shifting as your belly grows, which can affect balance.
This is also the stretch of pregnancy when many women feel their best. The nausea of the first trimester has usually passed, energy levels tend to rebound, and the physical discomforts of the third trimester haven’t arrived yet. Increased blood volume can give your skin a noticeable glow, though it can also cause occasional dizziness if you stand up too quickly. Some women experience round ligament pain, a sharp or pulling sensation on one or both sides of the lower belly, as the ligaments supporting the uterus stretch to accommodate its growing size.