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Stages of Pregnancy by Trimester

Infographic describing the stages of pregnancy and specific symptoms experienced during each trimester

Discover the changes each trimester brings, from the time sperms-meets-egg to when mom-meets-baby!

A typical full-term pregnancy lasts 40 weeks. Pregnancy is grouped into three stages called trimesters. You and your baby go through big changes during each 12- to 13-week trimester. Remember, every pregnancy is different. You may or may not experience some or all of the typical symptoms that come with hormone changes and a growing baby.

The stages of pregnancy are divided into trimesters, which include:

  • 1st Trimester: Begins at conception to 12 weeks
  • 2nd Trimester: Lasts from week 13 to week 27
  • 3rd Trimester: Begins at week 28 until birth

First Trimester — Conception to 12 Weeks

During the first trimester, not having your period is the first sign of pregnancy you’ll likely notice during your first trimester. Thanks to surging hormones, changes kick in during this stage that affects nearly every organ of your body.

Changes you may experience in the first trimester:

  • Extreme fatigue
  • Tender, swollen breasts
  • Food cravings or aversions
  • Nausea, vomiting (morning sickness)
  • Mood swings

During the first trimester, your baby grows from a single fertilized cell to a moving baby with growing limbs and developing organs.

Your baby’s development during the first 12 weeks:

  • Brain and spinal cord begin to form at 4 weeks
  • Heart begins to form and beats at a regular rhythm at around 8 weeks
  • Arms, legs, hands and feet begin to sprout at about week 6
  • External sex organs reveal by week 12 if your baby is a boy or a girl
  • Nerves and muscles begin to work together by week 12
  • Weighs about an ounce and is about 3 inches long

How can you accommodate changes during the first trimester?

This is the time to make a habit of taking good care of yourself. Your good health helps your baby as he or she continues to grow. You may need to get to bed earlier to fight fatigue. Eating smaller, more frequent meals can help with nausea.

Second Trimester — 13­–27 Weeks

Usually, during the second trimester, you and your body have happily adjusted to the hormone changes that come with pregnancy. Morning sickness eases up, or even disappears. You sleep better and have more energy. You’ll feel your baby’s first fluttering movements. If you haven’t shared the news of a baby on the way, a baby bump will do it for you toward the end of this stage.

Changes you may experience in the second trimester:

  • Mild swelling of the ankles and feet
  • Leg cramps
  • Achiness or pressure in the lower abdomen
  • Congestion
  • Varicose veins and hemorrhoids

With major organs and systems in place, the second trimester kicks off your baby’s growth spurt. As he grows, he’ll kick, roll and move his growing arms and legs.

Your baby’s development during weeks 13-27:

  • Begins to suck and swallow and can taste the food you eat through your amniotic fluid
  • Nails develop on fingers and toes
  • Brain has its most important growth
  • Eyelids begin to open, and eyelashes and eyebrows are visible
  • Weighs 2 to 3 pounds and is 13 to 16 inches long

How can you accommodate changes during the second trimester?

Keep treating yourself and your baby to the healthiest diet possible. To help reduce swelling, keep active. Put your feet up when you’re not moving, and avoid long periods of standing on your feet.

Third Trimester — 28–40 Weeks

This is the final stretch of your pregnancy, in more ways than one. Changes and symptoms you experienced during this stage likely continue and increase. Space in your abdomen gets tight. Your uterus gets bigger, pushing your stomach up, giving your lungs less room to expand and putting pressure on your bladder. Fatigue returns as it gets harder to find a comfortable position to sleep. But as the countdown to your baby’s birth moves from weeks to days, any discomforts will soon be just memories!

Changes you may experience in the third trimester:

  • Constipation, heartburn and indigestion
  • Stretch marks
  • Leaky breasts as your body gets ready to feed your baby
  • Vivid dreams
  • Braxton Hicks — “practice” — contractions

Your baby’s growth is on a fast track during the last weeks of pregnancy. Organs like the lungs and kidneys finish maturing, and the brain continues to develop.

Your baby’s development during weeks 28-40:

  • Sees and hears
  • Cartilage changes to bone
  • Sucks her thumb and cries
  • First poop develops in intestines
  • Begins to turn head-down and drop to get ready for delivery
  • Average birth weight is 6 to 9 pounds and is 19 to 21 inches long

How can you accommodate changes during the third trimester?

If you aren’t practicing Kegel exercises to strengthen your pelvic floor, now’s the time to start. Cutting back on drinking liquids close to bedtime helps cut down on trips to the bathroom at night. Sleeping on your left side is best for circulation — yours and your baby’s. Pillows between your legs, in front or behind you, can help give you support and make you more comfortable.

Ready to learn more? Check out our maternity classes at OhioHealth! Or are you looking for an OB/GYN? We can help!


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