What Is Pregnancy Trimester? Stages, Symptoms, and What to Expect in Each One
Jul 15, 2025
Have you ever wondered what people mean when they talk about pregnancy in “trimesters”? Maybe you’re newly pregnant and hearing terms like first, second, and third trimester for the first time. Or maybe you’re trying to get pregnant and want to understand what each phase really means. Pregnancy is an incredible journey, and knowing what to expect in each stage can help you feel more prepared, calm, and connected to your body.
In this guide, we will break down what is pregnancy trimester, the changes your body goes through, and what your baby is doing during each stage. Think of it as a friendly, supportive roadmap for your pregnancy journey.
What Is Trimester in Pregnancy?
Pregnancy is divided into three trimesters. Each trimester is about three months long and comes with its own set of changes, milestones, and experiences. Understanding what are the 3 trimesters of pregnancy makes it easier to follow your baby’s development and your own symptoms.
Here’s a quick look at each one:
First trimester: Weeks 1 to 12
Second trimester: Weeks 13 to 26
Third trimester: Weeks 27 to birth
These stages are nature’s way of pacing the incredible transformation of creating life. By the end, your body has grown into a tiny human and is ready for birth.
Pregnancy Trimesters Explained
Each trimester brings its own challenges and joys. Some women feel different symptoms in each one, while others feel fairly consistent throughout pregnancy. Let’s take a closer look at the stages of pregnancy trimesters so you know exactly what happens in each trimester of pregnancy.
First Trimester: The Early Days of Pregnancy
The first stages of pregnancy often feel like a whirlwind. From the moment of conception, your body begins to change rapidly to support your growing baby.
What to Expect in the First Trimester
Fatigue is common because your body is working overtime to grow a placenta.
Nausea or morning sickness may appear around week 6.
Breasts may feel tender, swollen, or tingly.
Mood swings are normal as hormones rise sharply.
You may notice food cravings or aversions.
These are some of the common symptoms during early pregnancy. Even though your baby is still tiny, they’re already developing vital organs, a beating heart, and tiny limb buds.
Second Trimester: The Golden Middle
Many women feel relief during the second trimester. Nausea often fades, and energy levels rise. This is when people start noticing your growing belly.
Second Trimester Pregnancy: What to Expect
A small baby bump starts to show.
Skin changes like a dark line down your belly (linea nigra) or pregnancy glow may appear.
You might feel the baby move for the first time, called quickening, around weeks 18 to 20.
Back pain or mild swelling can start as your uterus expands.
Your baby is growing rapidly too. Their fingerprints are forming, and they can even hear your voice.
Third Trimester: The Final Stretch
The third trimester begins at week 27 and lasts until delivery. Your baby is gaining weight quickly and practicing movements like kicking and stretching.
What to Expect During Third Trimester
You may feel more tired again as your body supports a nearly full-sized baby.
Braxton Hicks contractions, or “practice contractions,” can begin.
Sleep may be harder with a larger belly.
Shortness of breath or heartburn is common as your uterus presses against other organs.
This is when you’ll visit your healthcare provider more often to monitor your baby’s position and prepare for labor.
Pregnancy Trimester Chart
Trimester | Weeks | Baby’s Growth Focus | Common Symptoms |
First Trimester | 1 to 12 | Organ development, heartbeat starts | Nausea, fatigue, tender breasts |
Second Trimester | 13 to 26 | Growth, movement, senses develop | Back pain, glowing skin, first kicks |
Third Trimester | 27 to Birth | Weight gain, lung maturation | Swelling, contractions, sleep troubles |
This pregnancy trimester chart gives a simple overview of what’s happening each stage.
At What Week Does the Third Trimester Start?
The third trimester starts at week 27. From here, every week brings you closer to holding your baby. Your healthcare team will likely start checking the baby’s position and discuss signs of labor.
How to Know What Trimester You’re In
It can be easy to lose track with so many changes happening. To figure out your trimester:
Count the weeks from the first day of your last period.
Weeks 1–12 = First trimester
Weeks 13–26 = Second trimester
Week 27 and onward = Third trimester
Apps like Lunara (coming soon!) will help you track all these stages effortlessly.
What Happens in Each Trimester of Pregnancy?
Your body and baby are in constant motion. Here’s a closer look at key milestones.
First Trimester Milestones
The baby's heart starts beating (around week 6).
Major organs and the brain begin forming.
You may have your first ultrasound around week 8 to 12.
Second Trimester Milestones
The baby grows hair and eyebrows.
Sex may be determined at your 20-week scan.
The baby starts practicing swallowing and sucking.
Third Trimester Milestones
The baby's lungs mature.
The baby gains fat and prepares for birth.
You may notice them settling lower into your pelvis.
A Note from Lunara
Pregnancy is a beautiful journey, but it can feel overwhelming at times. That’s why Lunara is building tools to help you track your pregnancy stages, symptoms, and baby’s milestones. You’ll also get insights into nutrition, sleep, and self-care tips for every trimester. Join our waitlist now to be among the first to try it when we launch.
Final Thoughts
Pregnancy is made up of three unique trimesters, each with its own wonders and challenges. By understanding what is pregnancy trimester and what happens in each trimester of pregnancy, you can prepare and care for yourself through each stage. Remember, no two pregnancies are alike, and there is no “right” way to feel.
Take it one day at a time, listen to your body, and surround yourself with support. You are growing a new life, and that in itself is extraordinary.
Common Questions About Pregnancy Trimesters
Can I still exercise during the second stage of pregnancy?
Yes, with your doctor’s okay. Walking, swimming, and prenatal yoga are often safe.
What trimester is the hardest?
Many women say the first is hardest due to nausea and fatigue. But the third can also feel challenging as your body prepares for birth.
How long is each trimester?
Each trimester lasts about 12 to 14 weeks.
Do symptoms change each trimester?
Yes. Early pregnancy symptoms like nausea may fade in the second trimester, while new ones like swelling or back pain can appear later.
Have you ever wondered what people mean when they talk about pregnancy in “trimesters”? Maybe you’re newly pregnant and hearing terms like first, second, and third trimester for the first time. Or maybe you’re trying to get pregnant and want to understand what each phase really means. Pregnancy is an incredible journey, and knowing what to expect in each stage can help you feel more prepared, calm, and connected to your body.
In this guide, we will break down what is pregnancy trimester, the changes your body goes through, and what your baby is doing during each stage. Think of it as a friendly, supportive roadmap for your pregnancy journey.
What Is Trimester in Pregnancy?
Pregnancy is divided into three trimesters. Each trimester is about three months long and comes with its own set of changes, milestones, and experiences. Understanding what are the 3 trimesters of pregnancy makes it easier to follow your baby’s development and your own symptoms.
Here’s a quick look at each one:
First trimester: Weeks 1 to 12
Second trimester: Weeks 13 to 26
Third trimester: Weeks 27 to birth
These stages are nature’s way of pacing the incredible transformation of creating life. By the end, your body has grown into a tiny human and is ready for birth.
Pregnancy Trimesters Explained
Each trimester brings its own challenges and joys. Some women feel different symptoms in each one, while others feel fairly consistent throughout pregnancy. Let’s take a closer look at the stages of pregnancy trimesters so you know exactly what happens in each trimester of pregnancy.
First Trimester: The Early Days of Pregnancy
The first stages of pregnancy often feel like a whirlwind. From the moment of conception, your body begins to change rapidly to support your growing baby.
What to Expect in the First Trimester
Fatigue is common because your body is working overtime to grow a placenta.
Nausea or morning sickness may appear around week 6.
Breasts may feel tender, swollen, or tingly.
Mood swings are normal as hormones rise sharply.
You may notice food cravings or aversions.
These are some of the common symptoms during early pregnancy. Even though your baby is still tiny, they’re already developing vital organs, a beating heart, and tiny limb buds.
Second Trimester: The Golden Middle
Many women feel relief during the second trimester. Nausea often fades, and energy levels rise. This is when people start noticing your growing belly.
Second Trimester Pregnancy: What to Expect
A small baby bump starts to show.
Skin changes like a dark line down your belly (linea nigra) or pregnancy glow may appear.
You might feel the baby move for the first time, called quickening, around weeks 18 to 20.
Back pain or mild swelling can start as your uterus expands.
Your baby is growing rapidly too. Their fingerprints are forming, and they can even hear your voice.
Third Trimester: The Final Stretch
The third trimester begins at week 27 and lasts until delivery. Your baby is gaining weight quickly and practicing movements like kicking and stretching.
What to Expect During Third Trimester
You may feel more tired again as your body supports a nearly full-sized baby.
Braxton Hicks contractions, or “practice contractions,” can begin.
Sleep may be harder with a larger belly.
Shortness of breath or heartburn is common as your uterus presses against other organs.
This is when you’ll visit your healthcare provider more often to monitor your baby’s position and prepare for labor.
Pregnancy Trimester Chart
Trimester | Weeks | Baby’s Growth Focus | Common Symptoms |
First Trimester | 1 to 12 | Organ development, heartbeat starts | Nausea, fatigue, tender breasts |
Second Trimester | 13 to 26 | Growth, movement, senses develop | Back pain, glowing skin, first kicks |
Third Trimester | 27 to Birth | Weight gain, lung maturation | Swelling, contractions, sleep troubles |
This pregnancy trimester chart gives a simple overview of what’s happening each stage.
At What Week Does the Third Trimester Start?
The third trimester starts at week 27. From here, every week brings you closer to holding your baby. Your healthcare team will likely start checking the baby’s position and discuss signs of labor.
How to Know What Trimester You’re In
It can be easy to lose track with so many changes happening. To figure out your trimester:
Count the weeks from the first day of your last period.
Weeks 1–12 = First trimester
Weeks 13–26 = Second trimester
Week 27 and onward = Third trimester
Apps like Lunara (coming soon!) will help you track all these stages effortlessly.
What Happens in Each Trimester of Pregnancy?
Your body and baby are in constant motion. Here’s a closer look at key milestones.
First Trimester Milestones
The baby's heart starts beating (around week 6).
Major organs and the brain begin forming.
You may have your first ultrasound around week 8 to 12.
Second Trimester Milestones
The baby grows hair and eyebrows.
Sex may be determined at your 20-week scan.
The baby starts practicing swallowing and sucking.
Third Trimester Milestones
The baby's lungs mature.
The baby gains fat and prepares for birth.
You may notice them settling lower into your pelvis.
A Note from Lunara
Pregnancy is a beautiful journey, but it can feel overwhelming at times. That’s why Lunara is building tools to help you track your pregnancy stages, symptoms, and baby’s milestones. You’ll also get insights into nutrition, sleep, and self-care tips for every trimester. Join our waitlist now to be among the first to try it when we launch.
Final Thoughts
Pregnancy is made up of three unique trimesters, each with its own wonders and challenges. By understanding what is pregnancy trimester and what happens in each trimester of pregnancy, you can prepare and care for yourself through each stage. Remember, no two pregnancies are alike, and there is no “right” way to feel.
Take it one day at a time, listen to your body, and surround yourself with support. You are growing a new life, and that in itself is extraordinary.
Common Questions About Pregnancy Trimesters
Can I still exercise during the second stage of pregnancy?
Yes, with your doctor’s okay. Walking, swimming, and prenatal yoga are often safe.
What trimester is the hardest?
Many women say the first is hardest due to nausea and fatigue. But the third can also feel challenging as your body prepares for birth.
How long is each trimester?
Each trimester lasts about 12 to 14 weeks.
Do symptoms change each trimester?
Yes. Early pregnancy symptoms like nausea may fade in the second trimester, while new ones like swelling or back pain can appear later.