Pregnancy is often measured in different ways, which can be confusing for first-time parents. You’ll hear people talk about weeks, months, and trimesters, but how do they all fit together? Understanding the timeline of your pregnancy can help you better track your baby’s development and plan for key milestones. In this guide, we’ll break down pregnancy into weeks, months, and trimesters to make it easier to understand.

How Long Is Pregnancy?

A full-term pregnancy is typically around 40 weeks, starting from the first day of your last menstrual period (LMP). This may seem like more than nine months, but it accounts for the two weeks before ovulation and conception, making pregnancy last about nine calendar months or 10 lunar months (where each month is four weeks long).

Pregnancy by Weeks

Pregnancy is most commonly tracked by weeks. Doctors, midwives, and pregnancy apps often use weeks because they provide a more precise way to track your baby’s growth and important milestones.

• Weeks 1-13: First trimester
• Weeks 14-27: Second trimester
• Weeks 28-40: Third trimester​​

Here’s a breakdown of each trimester and what to expect:

The First Trimester (Weeks 1-13)

The first trimester marks the early stages of pregnancy when your baby is growing rapidly, though you may not be showing much yet.

• Weeks 1-4: Conception occurs, and the fertilized egg implants in your uterus.
• Weeks 5-6: Your baby’s heart starts beating, and the neural tube (which will become the brain and spinal cord) begins forming.
• Weeks 7-8: Major organs, such as the kidneys and liver, start to develop. You may start to feel common early pregnancy symptoms like nausea and fatigue.
• Weeks 9-12: Your baby’s limbs, fingers, and toes begin to form, and by the end of this trimester, all of the baby’s major organs are in place​​.

The Second Trimester (Weeks 14-27)

The second trimester is often called the “honeymoon phase” of pregnancy because many women start to feel better, with reduced nausea and more energy.

• Weeks 14-16: Your baby is growing fast, and you might start to show. The baby’s muscles and bones continue to develop.
• Weeks 17-20: Around this time, you may feel your baby move for the first time, known as “quickening.” Your mid-pregnancy ultrasound usually happens around week 20, where you may learn your baby’s gender if you choose.
• Weeks 21-24: Your baby’s senses, like hearing and taste, are developing, and they are starting to look more like a tiny newborn. They also start practicing breathing movements.
• Weeks 25-27: Your baby is gaining weight and preparing for the final stretch. By week 27, they are around 14 inches long and could survive outside the womb with medical support if born prematurely​​.

The Third Trimester (Weeks 28-40)

The third trimester is the final stretch of pregnancy, where your baby’s organs mature and they gain weight in preparation for birth.

• Weeks 28-32: Your baby’s brain and lungs continue to develop. They start moving into a head-down position for birth, and you may feel stronger kicks and movements.
• Weeks 33-36: Your baby is gaining weight rapidly, and their skin is becoming less wrinkled as they put on fat. They are getting ready for life outside the womb, and you may notice more frequent Braxton Hicks contractions.
• Weeks 37-40: Your baby is considered full-term by week 37. At this point, your body is getting ready for labor, and your baby’s lungs and brain are fully developed. Labor can start at any time​​.

Pregnancy by Months

Another way to measure pregnancy is by dividing it into months. Since pregnancy lasts around 40 weeks, it’s just over 9 calendar months. Here’s how the weeks break down into months:

• Month 1: Weeks 1-4
• Month 2: Weeks 5-8
• Month 3: Weeks 9-13
• Month 4: Weeks 14-17
• Month 5: Weeks 18-22
• Month 6: Weeks 23-27
• Month 7: Weeks 28-31
• Month 8: Weeks 32-35
• Month 9: Weeks 36-40​​.

Trimesters: Breaking Pregnancy Into Three Parts

Pregnancy is commonly divided into three trimesters, each with its own key milestones and developmental stages:

• First Trimester (Weeks 1-13): This is when most of the baby’s major organs develop, and you may experience the most noticeable early pregnancy symptoms like morning sickness, fatigue, and hormonal changes​.
• Second Trimester (Weeks 14-27): Often seen as the “easiest” trimester, your baby is growing rapidly, and you’ll likely start feeling baby kicks. Many women feel more energized during this time.
• Third Trimester (Weeks 28-40): This is the final stretch where your baby gains most of their weight. As your due date approaches, you might experience more physical discomfort, including back pain, swelling, and Braxton Hicks contractions​​.

Why Is Pregnancy Tracked by Weeks?

Healthcare providers often track pregnancy by weeks because it gives a more detailed timeline for measuring your baby’s growth, monitoring health milestones, and scheduling important tests like ultrasounds and glucose screenings. Since every baby develops at their own pace, tracking by weeks helps ensure that everything is progressing as it should.

Pregnancy is a journey that spans weeks, months, and trimesters, with each part of the timeline bringing new changes and exciting milestones. Whether you’re counting by weeks or months, understanding your pregnancy timeline helps you feel more prepared and connected to your baby’s development. As you move through each stage, keep in close contact with your healthcare provider to ensure a healthy and happy pregnancy.