The First Trimester: A Month-by-Month Timeline

By Kerry Weiss
Reviewed by Alyssa Quimby, M.D.
April 10, 2023

For the text version of this infographic, read on:

The First-Trimester Timeline

The first trimester is the first 3 months, or about 13 weeks, of pregnancy. Your body and mind are adjusting to being pregnant.

Month 1

For most people, the first sign of pregnancy is a missed period.

Other early signs of pregnancy include:

At-home pregnancy tests tend to be very accurate. Most can detect pregnancy just 10 days after conception.

Once you find out you’re pregnant, it’s time to make a few lifestyle changes:

  • Abstain from alcohol.
  • Quit smoking.
  • Limit caffeine consumption to less than 200 milligrams each day. That’s about the amount in a 12-ounce cup of coffee.
  • Avoid unpasteurized juice and dairy products.
  • Don’t eat raw or undercooked fish, meat, or eggs.
  • Avoid deli meat and raw sprouts, which can have harmful bacteria.
  • Take a prenatal vitamin daily.
  • Talk to your doctor about any medications or supplements you’re taking to make sure they’re safe for pregnancy.

By the end of the first month, your baby is only about ¼ inch long. It's referred to as an embryo.

Month 2

Around 6 to 10 weeks, you'll likely see your doctor for the first time. Your embryo’s heartbeat may be detected. Many people compare it to the sound of a galloping horse.

The risk of miscarriage drops to about 10% once you hear the heartbeat.

In your second month of pregnancy, symptoms tend to worsen. Morning sickness, in particular, tends to peak around weeks 9 through 14.

You may find yourself napping or going to bed earlier to combat pregnancy-related fatigue. Pregnant people should aim to get 8 to 10 hours of sleep each night.

At the end of the second month, your embryo will have developed more and will be called a fetus. It will be about 1 inch long and weigh around 1/30 ounce.

Month 3

New symptoms can range from acne to larger, darker areolas on the breasts.

You may start to notice your clothes getting a little tighter due to bloating and pregnancy-related weight gain.

You may be referred for an ultrasound called the nuchal translucency, which screens for chromosome defects.

The first trimester ends after week 13. By this time, the fetus will have started growing all their organs and limbs—they’ll develop more from here. Your fetus is about 4 inches long and weighs around 1 ounce.

You can look forward to the second trimester, when many people tend to feel better!


American College of Obstetricians and Gynecologists

Cleveland Clinic

March of Dimes

Mayo Clinic

National Health Service (UK)

National Institutes of Health

Planned Parenthood. Pregnancy Month by Month. Accessed October 6, 2022.

Tommy’s. Miscarriage Statistics. Accessed October 6, 2022.