How Your Body Changes, How Your Baby Grows

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A full-term pregnancy lasts about 40 weeks. You begin counting from the start of your last menstrual period. That’s about 9 calendar months. The 9 months are divided into 3 parts. Each part is called a trimester. The trimester charts that follow show changes in your body. They show how your baby grows.

First Trimester (Months 1-3, Weeks 1-13)

Changes in Your Body

•  Your hormones change.

•  Your body makes more blood and body fluids.

•  You may feel very tired.

•  You pass urine more often.

•  You may have an upset stomach, or throw up (morning sickness). This can happen any time of the day.

•  You may feel light-headed or dizzy.

•  You gain a few pounds. The average is 3 or 4 pounds. Your clothes begin to feel a little tight.

•  Your moods can vary. You may feel happy and elated. You may also feel sad, cross, or anxious.

•  Your breasts may change.

– They may get bigger.

– They may get sore and tender.

– Your nipples get darker. They may stick up more.

How Your Baby Grows

Your baby starts out as a single cell. The cell is formed when your egg and your male partner’s sperm meet. That one cell divides into many cells. These attach to the wall of your uterus. Some of the cells form the placenta. The rest become the embryo. That’s what the unborn baby is called from week 4 to week 8. After 8 weeks, it is called a fetus. By the end of the first trimester, your baby:

•  Is about 3 to 4 inches long

•  Weighs about 1 ounce

•  Has all its internal organs and limbs. Its heart beats.

•  Has a large head compared to the rest of its body. Its eyes are closed.

•  Begins to develop sex organs

•  Has well-formed fingers and toes. Fingernails and toenails are forming.

•  Can move in the uterus. You can’t feel that yet, though.

Second Trimester (Months 4-6, Weeks 14-27)

Changes in Your Body

•  You probably feel really good during this trimester. Most women do.

•  You start to look pregnant as your belly expands. You gain about a pound a week. Loose or maternity clothes feel best.

•  Your heart beats stronger. This helps push the extra body fluids around your body. It helps push them into the placenta, too.

•  You start to feel your baby move. This usually starts between weeks 15 and 20 with a first baby. It may come earlier than that with babies after the first one. First you feel flutters. Then you feel kicks.

•  Your breasts get ready to make milk.

•  Your uterus starts to stretch out and get thinner.

•  You may notice that you have:

–  Backache

–  Constipation

–  Headache

–  Mood swings

–  Braxton-Hicks contractions

–  Mild swelling of the ankles and feet

–  Less morning sickness or none at all

–  Less need to pass urine

–  Bigger appetite

–  Heartburn

–  Larger veins in your hands and arms

–  Stretch marks on your breasts and belly

–  Leg cramps at night

None of these is apt to change your sense of well-being, though.

How Your Baby Grows

Your baby begins to grow fast. Its organs mature. By the end of the second trimester, your baby:

•  Is about 11 to 14 inches long

•  Weighs about 2 to 2-1/2 pounds

•  Swallows

•  Sucks its thumb

•  Moves and kicks

•  Has wrinkly skin. Its skin is covered by a thick, white coating called vernix.

•  Has hair growing on its head

•  Has teeth forming in the jawbone

•  Can open and close its eyelids

•  Has eyes that are almost fully developed. Eyebrows and eyelashes start to grow.

Third Trimester (Months 7-9, Weeks 28-40)

Changes in Your Body

You gain about a pound a week until the final few weeks. Then you may stop gaining weight or lose a pound or two. As the baby grows, your uterus and belly expand. You feel lots of pressure on your bladder. You need to pass urine more often.


The baby pushes up on the bottom of your rib cage. The baby pushes up on the diaphragm. This can cause you to feel short of breath.


The baby makes stronger movements and moves more often. You can feel its head, elbows, and feet as they push against your belly. You may be able to see the baby’s kicks! You may notice that:

•  You feel hot and you sweat more than usual.

•  A yellow liquid leaks from your breasts.

•  Your hands and feet swell.

•  Your navel may look flat or stick out.

•  You feel tired.

•  You have mood swings.

Toward the very end of this trimester (near your due date):

•  You may feel your uterus getting tight and hard.

•  You may have “practice” contractions. These stop when you move your body or walk around.

•  The baby “drops” into your pelvis. It is easier for you to breathe. It also makes you need to pass urine more often.

•  You lose the mucus plug. You usually lose it shortly before delivery. It’s called bloody show then. You may notice it as a thick, stringy discharge for days. Or you may pass a big clump that looks like a wet cotton ball. Some women never notice the bloody show.

How Your Baby Grows

Your baby keeps growing and gaining weight. During this trimester, your baby:

•  Grows to about 20 inches long

•  Gains weight to 7 pounds or more

•  Fills the uterus

•  Opens and closes its eyes

•  Responds to light and sound

•  Moves a lot. Its movements are more like rolls and turns instead of kicks. These may slow down close to labor. But the baby does not stop moving before birth. Tell your health care provider if you notice a big decrease in your baby’s activity.

•  Settles further down into your pelvis. Your baby is getting ready to be born!

This website is not meant to substitute for expert medical advice or treatment. Follow your doctor’s or health care provider’s advice if it differs from what is given in this guide.


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