What do I need to know about each trimester of pregnancy?

From the moment you see those two pink lines, it can feel like there’s something new to learn every day. One of the first things you’ll likely hear is that pregnancy is measured in three stages: the first, second and third trimesters. But what actually happens during each one?

Pregnancy lasts 40 weeks, and it’s broken up into trimesters of about 13 weeks each.

While every pregnancy is different, each trimester brings exciting milestones for both you and your growing baby. Vanessa Foster, MD, OB/GYN, offers a trimester-by-trimester breakdown so you know what to expect as pregnancy progresses.

“Each trimester, we have specific goals that need to be accomplished,” said Dr. Foster. “As your baby grows and changes, your prenatal care changes too. Our goal is to support you through each stage and make sure both you and your baby are healthy.”

First Trimester (Weeks 1-12)

The first trimester starts the moment your baby is conceived and lasts until you are about three months pregnant.

First Trimester Symptoms

During the first trimester, pregnancy hormones rise quickly, and that’s often why you may not feel quite like yourself. Common symptoms in the first trimester include:

• Morning sickness or nausea (which can happen any time of day)
• Fatigue
• Breast tenderness
• Frequent trips to the bathroom
• Mood swings or feeling more emotional than usual

How Your Baby is Growing

By the end of the first trimester, your baby will be about the size of a grape. It will have started to form the neural tube, which develops into the brain and spinal cord. Your baby will also start to develop ears and eyes at the end of the first trimester.

Typically, you will not feel your baby moving during the first trimester, though you shouldn’t have to wait much longer.

Your Prenatal Appointments

As for your care, you’ll see your OB/GYN about every four weeks. You can expect to have plenty of blood drawn for prenatal testing as part of your first trimester screening. Your provider may offer genetic testing at this stage and take vaginal cultures to make sure you don’t have any infections.

A first trimester ultrasound is done to confirm your pregnancy dates. This is often you’re your provider can determine whether you are pregnant with multiples. Around four to seven weeks of pregnancy, you can also hear your baby’s heartbeat.

You’ll also talk about healthy habits during pregnancy, including foods to eat and medications to avoid. Your provider may recommend limiting foods that carry a higher risk of foodborne illness, such as deli meats and soft cheeses, avoiding high-mercury fish like swordfish, starting a daily prenatal vitamin and choosing pregnancy-safe pain relief medications for common illnesses.

When to Call Your Provider

While many first-trimester symptoms are completely normal, it’s always OK to call your provider if something doesn’t feel right.

Contact your provider immediately if you experience vaginal bleeding or if nausea and vomiting become so severe that you can’t keep food or fluids down or begin feeling weak or dehydrated.

“The first trimester is an important time because so much of your baby’s early development is happening,” said Dr. Foster. “That’s why we encourage parents to schedule prenatal care as soon as they know they’re pregnant. Early visits help us support both mom and baby from the very beginning.”

Second Trimester (Weeks 13-27)

Many parents lovingly call the second trimester the “honeymoon phase” of pregnancy, where you may finally start feeling more like yourself again. Your energy often returns, your baby bump becomes more noticeable and, best of all, you’ll likely feel your baby move for the first time.

Second Trimester Symptoms

For many women, morning sickness begins to fade during the second trimester, and everyday activities start feeling easier again. As your uterus grows, your baby bump becomes more noticeable, and you may find it’s time to swap your favorite jeans for maternity clothes.

Some of the most common second-trimester changes include:

• More energy and less nausea
• A growing baby bump
• Feeling your baby’s first flutters or kicks, usually between 14 and 20 weeks
• Round ligament pain, which can feel like a quick, sharp pain or pulling sensation in your lower abdomen as your uterus stretches

Those first movements can be easy to miss at first.

“It might be difficult to tell if that’s the baby moving, or if it’s your stomach growling. It’s a little hard to tell at first,” Dr. Foster said. “But as the pregnancy progresses, you’ll definitely be able to tell the difference.”

You can also expect to gain weight more steadily during this trimester, typically about a half pound to a pound each week, though every pregnancy is different.

How Your Baby is Growing

By the end of the second trimester, nearly all of your baby’s major organs have formed, and they’re growing stronger every day. Their hearing continues to develop, meaning they may begin responding to familiar voices and sounds from outside the womb. They’re becoming more active too, stretching, kicking and even practicing swallowing and breathing movements.

Your Prenatal Appointments

During the second trimester, you’ll continue seeing your OB/GYN regularly, typically every two to four weeks depending on your pregnancy and your provider’s recommendations.

One of the biggest milestones is your anatomy scan, usually performed around 18 to 22 weeks. This detailed ultrasound allows your provider to carefully examine your baby’s organs, growth and development. If you’d like to know your baby’s sex, this is often when you’ll find out.

Later in the trimester, you’ll also have a glucose screening test to check for gestational diabetes. While you’ll continue having routine prenatal visits, you’ll likely notice fewer tests than during the first trimester unless your provider recommends additional monitoring.

When to Call Your Provider

Once you begin feeling regular movement, it’s a good idea to become familiar with your baby’s normal activity. If you notice a significant decrease in movement or have concerns about how your baby is doing, don’t hesitate to call your provider.

“Your baby is a person, and that person should move in there every now and then,” said Dr. Foster. “They sleep, they get the hiccups and they move around. If something feels different than what’s normal for your baby, we’d much rather you call than spend time worrying.”

Third Trimester (Weeks 28-40)

The third trimester is all about the final countdown. As your due date gets closer, you may feel equal parts uncomfortable and eager to meet your baby. While your body is working harder than ever, your prenatal appointments become more frequent to help make sure both you and your baby are doing well.

Third Trimester Symptoms

By now, your growing baby bump may make everyday tasks feel a little more challenging. As your center of gravity shifts, you may notice more back pain, pelvic pressure or occasional cramping. Braxton Hicks contractions, or “practice contractions,” also become more common as your body prepares for labor.

Other common third-trimester changes include:

• Swelling in your feet, ankles or hands
• Difficulty getting comfortable or sleeping
• Feeling the urge to organize the nursery, pack your hospital bag or prepare for baby’s arrival (also known as “nesting”)

You’ll likely continue gaining about a half pound to a pound each week until delivery, though every pregnancy is different.

How Your Baby is Growing

During these final weeks, your baby’s biggest job is growing and getting ready for life outside the womb. Their lungs continue to mature, they gain body fat to help regulate their temperature after birth and, in most pregnancies, they’ll gradually move into a head-down position in preparation for delivery.

By around 37 weeks, your baby is considered full term and ready to make their debut whenever the time is right.

Your Prenatal Appointments

During the third trimester, you’ll see your OB/GYN more frequently, often weekly as you approach your due date. These visits include checking your blood pressure, monitoring your baby’s heartbeat and growth, and watching for signs that your body is preparing for labor.

Between 36 and 37 weeks, you’ll also have a Group B strep (GBS) screening. This routine test checks for bacteria that are common in healthy adults but can make newborns sick during delivery. If your test is positive, your care team will talk with you about antibiotics during labor to help protect your baby.

When to Call Your Provider

As your due date approaches, your provider will go over the signs of labor. If you notice a decrease in movement, experience vaginal bleeding, have a gush or steady leak of fluid, or think you may be in labor, contact your provider right away.

“By the third trimester, we’re preparing for one of life’s biggest moments,” said Dr. Foster. “Our goal is to help you feel informed and confident as you get ready to welcome your baby.”