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Pregnancy Trimesters: Each Stage of Pregnancy

Pregnancy Trimesters: Each Stage of Pregnancy
Third trimester pregnant woman on the beach

When you are expecting or thinking about conceiving, you may wonder what happens through each of the pregnancy trimesters. As the stages of pregnancy progress, so do the changes within the mom and baby.

By Chelsea Skaggs, Postpartum Togeter

While no two pregnancies are the same, there are things that usually happen through the weeks. 

There are three trimesters in pregnancy. Pregnancy is an average of 40 weeks, so the pregnancy trimester weeks are each between 13 and 14 weeks.

  • First trimester: Weeks 1-13
  • Second trimester: Weeks 14-26
  • Third trimester: Weeks 27-40

Your estimated due date is calculated based on your last period so to find it, add 40 weeks to the date of your last period. From there, you can calculate when you will be in each of the stages of pregnancy.

Mom’s Changes in the First Stage of Pregnancy

In the first stage of pregnancy, months 1-3, there are many changes inside a new mom. You may experience one or more symptom of early pregnancy:

  • Nausea
  • Fatigue
  • Frequent urination
  • Breast tenderness
  • Cravings
  • Mood swings
  • Constipation
  • Headaches
  • Weight gain/loss

In the first trimester, many of your symptoms are a hormonal response to the pregnancy. As the body starts to nourish and grow a new human, the body adjusts to these needs. Don’t be surprised if you feel “off” for parts of the first trimester as something totally new happens in your body.

When you discover you are pregnant, you want to start taking prenatal vitamins and cease any alcohol or tobacco consumption. You also want to get folic acid in your diet which aids baby’s early development. This is also the perfect time to start nesting for little one – prepare the nursery as you start your pregnancy journey.

Baby’s Changes in the First Trimester

Even before many women know they are pregnant, many parts are developing and growing in a new baby:

  • Nervous system
  • Heart
  • Arm and leg buds
  • Fingers and toes
  • Reproductive organs
  • Facial features
  • Umbilical cord

At 12-13 weeks, babies average 3 inches long and weigh one ounce!

What Happens in the Second Trimester?

Mom’s Changes in the Second Stage of Pregnancy

Some women refer to the second trimester as the “golden trimester” since the early symptoms tend to wear off.  During the second stage of pregnancy, women notice:

  • Back pain
  • Constipation
  • Heartburn
  • Darkened areolas
  • Leg cramps
  • Linea nigra
  • “Mask of pregnancy”
    As your uterus grows and your body expands to hold baby, it’s a great time to feel cute with fun maternity clothes.

Baby’s Changes in the Second Trimester

In the second trimester, the baby is noticeably moving around and continuing to grow. During this stage of pregnancy your baby is developing:

  • Muscoskeletal system
  • Skin (though still translucent)
  • Fine hair (lanugo)
  • Vernix
  • Eyebrows
  • Eyelashes
  • Fingernails
  • Toenails
  • Fingerprints
  • Footprints
  • Head hair

Your baby is learning to:

  • Suck
  • Taste
  • Sleep in cycles

At 26 weeks, your baby is around 12 inches long and 1.5 lbs.

During the second trimester, you will start to feel baby kick and move inside of you. This can be both exciting and uncomfortable! This is a great time to read to your growing baby as he/she starts to recognize your voice.

Parenting books for pregnancy trimesters

What Happens in the Third Trimester?

Mom’s Changes in the Third Stage of Pregnancy

As you enter the third and last stage of pregnancy, your baby is growing and your body is preparing for birth. You may experience:

  • Trouble sleeping
  • Colostrum leaking
  • Pressure as baby drops
  • Hemorrhoids
  • Swelling
  • Varicose veins

Baby’s Changes in the Third Trimester

Soon you will have a newborn. During this time, your baby grows:

  • Bone strength
  • Ability to open and close eyes
  • Mineral storage
  • Thickened vernix
  • Body fat developing

During the third trimester, your baby will grow an average of ½ pound per week. Most births occur between 38-41 weeks. If you are planning  a babymoon or other travel, talk with your provider about when it is still safe to travel.  As you prepare with your friends and family, it’s a great time to choose your favorite first outfits for baby boy and baby girl!

Baby girl outfit inspiration - knit dusty rose sets
Baby boy outfit inspiration - blue outfits

One thing to know about newborns is no two are exactly the same and they do not always follow the “rules.” Enjoy and capture each stage as you learn how you and baby grow through the trimesters of pregnancy. 

Postpartum Together founder Chelsea Skaggs

Chelsea Skaggs

About The Author


Senior public relations manager at Zulily

1 Comment

  1. Avatar

    It’s time to throw away all of those cookie-cutter date questions (What’s your sign, what are your hobbies, what’s your favorite color etc.


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