The Expectant Mom’s Guide to Pregnancy Trimesters

Content medically reviewed by Sara Luoma, APRN, CNP

If you just found out you’re pregnant, you probably have many questions. The months ahead will be filled with excitement, milestones, and probably a few seemingly odd symptoms. Learn what to expect as you move through the pregnancy trimesters.

Pregnancy Basics

“Pregnancy begins with the first day of your last menstrual period,” said Sara Luoma, APRN, CNP at Essentia Health. “Implantation—when a fertilized egg leaves the fallopian tube and attaches to the uterine lining—takes place about two weeks later.”

Pregnancy has three trimesters –

• The first trimester lasts through the first 13 weeks of pregnancy.
• The second trimester starts at 14 weeks and continues through 27 weeks.
• The third trimester starts at 28 weeks and continues through 40 weeks.

Keeping up with prenatal appointments can help you keep a close eye on your health as your baby grows.

The First Trimester (Weeks 1–13)

In the first trimester, you’re setting the foundation for a healthy pregnancy.

How You Might Be Feeling

During the first weeks of pregnancy, your hormones run amuck, causing the symptoms that often clue you in that you’re pregnant –

• Breast tenderness
• Digestive issues
• Fatigue
• Food cravings
• Frequent urination
• Headaches
• Leg cramps
• Mood swings
• Nausea or vomiting

Mild cramping can also occur as the uterus grows, but if you experience cramping that’s severe or accompanied by symptoms such as vaginal bleeding, let your medical provider know.

Taking Care of Yourself

It can be difficult if you don’t feel well, but moving your body as much as you can, when you can is important. Physical activity can keep you healthy and improve uncomfortable pregnancy symptoms.

Keep your energy up with a diet filled with fruits, vegetables, lean proteins, whole grains, and healthy fats. You’ll also want to take a prenatal vitamin or other provider-approved supplements daily.

What’s Happening With Your Baby

During this stage of pregnancy, your baby’s organs and other body parts begin to develop, including their –

• Brain
• Cardiac tissue
• Eyelids
• Fingernails
• Genitals
• Kidneys
• Liver
• Lungs
• Pancreas

By the end of week 12, most babies are about 2.5 to 3 inches long and roughly the size of a plum.

Medical Milestones

During some of your first prenatal appointments, you’ll have a physical exam and urine and blood tests. One of those tests, an Rh factor blood test, checks for a certain protein on the surface of your red blood cells.

Using the date of your last period and possibly an ultrasound scan, your provider will determine your estimated due date. If you have any existing medical conditions or other risk factors, your provider may recommend additional prenatal screenings or seeing a provider who specializes in high-risk pregnancy.

During this appointment, ask your provider any questions you have about pregnancy, including what symptoms you might experience and what tests you should have.

The Second Trimester (Weeks 14–27)

You may feel more like yourself during the second trimester, even as your baby and your belly keep growing.

How You Might Be Feeling

Morning sickness often goes away during this trimester, and you might feel more energized. You may also experience some new symptoms –

• Darkening areolas
• Itching on your abdomen, palms, or the soles of your feet
• Lower back or pelvic pain
• Patches of dark skin down your abdomen
• Stretch marks
• Swelling of your ankles and fingers

“Don’t be surprised if you feel tugging sensations or discomfort in your abdomen at times during the second trimester,” Luoma said. “This is often round ligament pain, caused by stretching in the ligaments that support the uterus.”

Taking Care of Yourself

Keep a close eye on how you’re feeling and check in with your provider if you notice anything that seems out of the norm. While some swelling is normal, sudden swelling can be a sign of preeclampsia, a serious medical condition.

Don’t push yourself too hard during the second trimester, even if you’re feeling better than you did during your first. Listen to your body and rest when needed.

What’s Happening With Your Baby

During the first trimester, your baby began developing. In the second trimester, everything gets more detailed –

• Eyelids can open and close
• Skin thickens
• The digestive system is operational
• The lungs are fully formed
• The nervous system is developing
• Toenails form

By the end of the second trimester, most babies are about the size of a head of cauliflower.

Medical Milestones

During monthly appointments, your provider will monitor your health and your baby’s development. Second trimester appointments include –

• Taking belly measurements beginning at week 20 to check your baby’s growth
• Glucose screening test to check for gestational diabetes
• Ultrasound scan to check development and look for abnormalities

If your initial glucose screening test shows you have high blood sugar, you may need a longer follow-up test to see if you have gestational diabetes.

The Third Trimester (Weeks 28–40)

You’re now in the final stretch of your pregnancy.

How You Might Be Feeling

During the third trimester, it’s common to experience even more new symptoms –

• Difficulty sleeping
• Heartburn
• Hemorrhoids
• Increasingly frequent urination
• Shortness of breath

Most of these symptoms are caused by your growing belly. As your baby gets bigger, it puts more pressure on your organs, which leads to uncomfortable symptoms.

Taking Care of Yourself

Now that you’ve reached the home stretch, it’s even more important to listen to your body. If you have any symptoms that seem concerning, check in with your pregnancy provider.

Because it can be difficult to find a comfortable position during this stage, it might be helpful to support your body as you sleep or rest. If you experience Braxton-Hicks contractions, which are sporadic contractions preparing your body for labor, you can usually ease them by drinking water or changing your position.

What’s Happening With Your Baby

By the third trimester, your baby is almost ready to be born –

• Bones have hardened, limbs are fattening up, and your baby’s head may have some hair.
• The circulatory and musculoskeletal systems are complete.
• The lungs and brain have substantially developed.
• Your baby can kick, grasp, stretch, and make many other movements.

Your baby is considered full term when you hit the 39-week mark. 

Medical Milestones

By the time you’re in the third trimester, you’ll be seeing your pregnancy provider every two weeks. Beginning at 36 weeks, you’ll see your provider weekly.Third trimester appointments may include –

• Cervical checks
• Nonstress test to check the baby’s oxygen and response to stimulation (if you’re overdue or the provider has concerns about the baby’s health)
• Tests and treatments for health problems that could pose risks for your baby, such as Group B Streptococcus
• Ultrasound scan to look at your baby’s positioning
• Vaccinations, including the Tdap vaccine

If you still have questions about anything labor- and delivery-related, speak up during these appointments. Your provider can talk with you about the signs of labor, as well as what to do when you go into labor.

Take a deep breath now, mama. It’s nearly time to greet your baby.