What Happens at 4 Months Pregnant | Body & Baby Changes

Four months pregnant (weeks 14–17) is when many women enter the second trimester, baby’s facial features refine, hair begins to grow.

You’ve probably heard the second trimester called the “golden period” of pregnancy, the stretch when morning sickness fades and energy returns. That’s true for many women, but the fourth month also brings its own surprises — new aches, shifting organs, and the first real hints that your baby is active in there.

Here is what’s actually happening inside your body and your baby’s body during weeks 14 through 17, from the physical milestones to the symptoms that catch most moms off guard.

Baby’s Development at Four Months

By the end of month four, your baby is about 5 inches long and weighs roughly 5 ounces — roughly the size of a small avocado. The major structural growth is well underway.

Eyelids, eyebrows, eyelashes, and nails are forming. Fine hair called lanugo begins to cover the skin. The roof of the mouth is fully formed, and the baby can stretch, make faces, and even suck a thumb. All of that happens before most women feel a single kick.

The skeleton is hardening, and the baby’s sex organs are developed enough that an ultrasound technician may be able to tell the sex — though many practices wait for the anatomy scan at 18 to 20 weeks for a clearer look.

Why the Fourth Month Feels Different

You might expect to sail through weeks 14 to 17 without trouble, but the growing uterus is busy pushing your other organs around. That shift alone can create a whole new set of sensations. Common symptoms at this stage include:

• Heartburn and indigestion: Hormones relax the valve between your stomach and esophagus, and the expanding uterus presses upward.
• Round ligament pain: A sharp or dull ache on one or both sides of the lower belly, especially when you change positions quickly.
• Backache and pelvic pressure: Your center of gravity shifts as the uterus grows, and ligaments soften in preparation for birth.
• Nosebleeds and bleeding gums: Increased blood flow to mucous membranes makes tiny vessels more prone to breaking.
• Varicose or spider veins: Extra blood volume and pressure from the uterus can cause veins in the legs and elsewhere to enlarge.

Most of these symptoms are normal, but they can be uncomfortable. Staying hydrated, eating smaller meals, and moving gently may help manage them.

When You’ll Feel Your Baby Move

One of the most anticipated moments of the fourth month is quickening — the first time you feel your baby move. Quickening typically happens between 16 and 20 weeks, though first-time mothers often feel it closer to 20 weeks, while women in subsequent pregnancies may notice it earlier.

Many women describe the sensation as flutters, bubbles, or tiny pulses — so subtle that it’s often mistaken for gas. A thinner body type or an anterior placenta can also affect how early you feel movement. Healthline’s guide on 4 months pregnant symptoms notes that these early flutters are rarely painful; they’re more of a gentle tap from inside.

If you haven’t felt movement by week 20, that’s still within the normal range for first pregnancies. Mention it at your next prenatal visit, but there is usually no cause for concern.

The Anatomy Scan at 18 to 20 Weeks

Around the end of the fourth month or early in the fifth, your provider will typically schedule a detailed anatomy ultrasound. This scan checks the baby’s organs — heart, brain, kidneys, spine — as well as the limbs and overall growth. The technician also looks at the placenta, amniotic fluid levels, and the baby’s position.

For many parents, this is also the scan where they learn the baby’s sex, if they choose. But beyond that, the anatomy scan gives your provider a comprehensive picture of whether development is on track. According to most guidelines, this is considered the most important ultrasound of the second trimester.

Weight Gain and Body Changes During the Second Trimester

Your baby starts gaining weight more quickly during these weeks, roughly half a pound per week later in the second trimester, per the Office on Women’s Health. At the same time, your own body is changing — your uterus rises above the pubic bone, and by week 16 it’s about halfway between your pubic bone and belly button.

That upward growth is why you may start to feel shortness of breath even before the baby gets big: the uterus is nudging your diaphragm and pushing on your lungs. The same shifting can cause constipation and the backache mentioned earlier. Womenshealth.gov’s page on baby weight gain second trimester explains that rapid growth in the second half of pregnancy supports the baby’s brain, bones, and organ maturation.

Your appetite may increase noticeably during this period as your body works harder to support the growing baby. Eating nutrient-dense foods and staying well hydrated can help you manage energy levels and reduce pregnancy discomforts.

The Bottom Line

The fourth month marks a real turning point — your baby is developing features that make them look more like a newborn, and you may finally feel those first flutters that confirm something is moving in there. Symptoms like heartburn, leg cramps, and round ligament pain are common but manageable. If anything worries you or feels severe, your obstetrician or midwife can help sort out what’s normal for your specific pregnancy.

Remember, every pregnancy is a little different — quickening timing varies, symptoms come and go, and your bloodwork and ultrasound results will guide your individual care plan, so checking in with your provider about what you’re experiencing is always the best next step.