What Is Gestational Age and How Do You Calculate It?

Jan 21, 2025

Pregnancy is an exciting journey filled with many milestones. One of the most important things to understand during pregnancy is gestational age. But what does gestational age mean, and how is it calculated? Let’s break it down.

What Is Gestational Age?

Gestational age is the most common way to measure how far along a pregnancy is. It tells us how many weeks and days have passed since the first day of the pregnant person's last menstrual period (LMP).

Doctors and nurses use gestational age to:

  • Track the baby’s growth and development.
  • Estimate the baby’s due date.
  • Schedule important tests and check-ups.

When a baby is born, gestational age helps the healthcare team understand if the baby arrived early, on time, or late.

How Is Gestational Age Calculated?

Gestational age is usually measured in weeks. A full-term pregnancy lasts about 40 weeks, but it can range from 37 to 42 weeks.

There are a few ways to calculate gestational age:

1. Using the Last Menstrual Period (LMP)

The most common method is to count from the first day of the mother’s last menstrual period. Here’s how it works:

  1. Write down the first day of your last period.
  2. Count forward by weeks to see how far along you are.

For example:

  • If your last period started on January 1st and today is March 1st, you’re about 9 weeks pregnant.

2. Ultrasound Nurse doing ultrasound diagnosis on pregnant patient

Sometimes, it’s hard to remember the date of your last period. That’s okay! In these cases, an ultrasound can help. During an ultrasound, the doctor or technician measures the baby. This measurement helps estimate how many weeks along the pregnancy is.

3. Pregnancy Wheel

Doctors often use a pregnancy wheel, a simple tool that shows how many weeks pregnant you are based on your LMP. It also shows the estimated due date.

Why Is Gestational Age Important?

Knowing the gestational age helps ensure both mom and baby stay healthy. Here’s why it matters:

  • Growth Tracking: Doctors can make sure the baby is growing at the right pace.
  • Test Timing: Some tests, like ultrasounds and glucose screenings, are done at specific stages of pregnancy.
  • Delivery Planning: It’s important to know if a baby is premature (born before 37 weeks) or post-term (born after 42 weeks).

Gestational Age vs. Fetal Age

Sometimes, people confuse gestational age with fetal age. Here’s the difference:

  • Gestational Age: Counts from the first day of the last menstrual period. This includes about two weeks before the baby is conceived.
  • Fetal Age: Starts from the day the baby is actually conceived. This is usually about two weeks after the last period.

So, if your gestational age is 10 weeks, the baby’s fetal age is about 8 weeks.

How Variety Care Can Help

At Variety Care, we’re here to support you every step of the way. Our caring team offers:

  • Prenatal Visits: Regular check-ups to monitor your health and the baby’s growth.
  • Ultrasounds: To see how your baby is doing and measure gestational age.
  • Education: Information about pregnancy, labor, and delivery.
  • Support: Answers to all your questions so you feel confident and prepared.

When Should You See a Doctor?

If you think you might be pregnant, schedule an appointment as soon as possible. Early care is important for a healthy pregnancy. Our team will help you calculate your gestational age and create a plan for a safe and happy pregnancy.