Pregnancy Stages: Your Baby, Your Body

A trimester-by-trimester look at how you and your baby are growing.

Reviewed by Hansa D. Bhargava, MD on May 14, 2011
From the WebMD Archives

Congratulations, you're pregnant! And you're probably curious and a little anxious about what's going to happen with your body and your baby over the next nine months. Here are some highlights.

The First Trimester (You've Got a Secret)

For most women, especially first-time moms, it's almost impossible for anyone to tell they're pregnant during the first trimester. As a brand-new expectant mother, you're not showing much, if at all, and the only telltale outward sign might be that smile you just can't suppress.

But inside, both your baby and your body are already working at top speed, like the Apple factory before a new iPad launches. During the next 13 weeks, your baby will:

  • Grow from a tiny cluster of cells called a blastocyst (about the size of the head of a carpenter's nail) at week three of pregnancy to about 3 inches long (think the length of your car key) by week 12.
  • Develop pigment in her eyes (still hidden behind sealed lids), form a tiny tongue with taste buds, and build a full four-chambered heart beating at about 180 beats per minute.
  • Form all of her major organs and body systems -- a critical time of structural development. The period between eight and 10 weeks' gestation is perhaps the single most crucial time for fetal development, says Annette Perez-Delboy, MD, assistant professor of obstetrics and gynecology at Columbia University Medical Center and a maternal-fetal medicine specialist.

Meanwhile, there's a lot going on with you, too:

  • Your heart is rerouting much of its effort toward baby's temporary digs, your uterus. By the end of the first trimester, a significant amount of your cardiac output goes to the uterus.
  • Your uterus is expanding from the size of a closed fist at conception to about the size of a small melon at 13 to 14 weeks.
  • You may be noticing some of the first physical signs of pregnancy: breasts that are sore or tingle at the slightest touch, skin that's drier or oilier than usual, and "morning sickness" -- which may or may not restrict itself to the morning hours. As many as 70% to 80% of pregnant women have it, but not feeling morning sickness doesn't mean there's anything wrong with the baby.

The Second Trimester (Pregnancy Honeymoon)

Doctors often call this the "honeymoon trimester." Many women have put the nausea, sore breasts, and fatigue of the first trimester in the rear-view mirror. You're big enough to proudly show off a growing belly but not yet so ungainly that turning over in bed requires help.

During this trimester, your baby will:

  • Triple in length -- more or less -- from about 6 inches at week 14 or 15 to about 14 inches at 27 weeks. At the start of this trimester, she'll be about the size of a peach. By the end, she'll be more like an eggplant.
  • Begin to hear the cacophony of sounds inside your uterus -- your pounding heart, swooshing blood as it rushes through your veins, and the gurgles of your stomach digesting lunch.
  • Develop fine, downy hair called lanugo, which usually shows up first around the eyebrows and upper lip.

You're changing, too -- inside and out:

  • Most pregnant women begin to "show" during the second trimester. You likely gained less than 5 pounds during your first trimester, but now the number on the scale is edging relentlessly upward. As your second trimester proceeds, you'll gain an average of 1 to 2 pounds per week.
  • Your internal organs will relocate to accommodate your growing uterus. Your rib cage will move upward by as much as 2 inches.

The Third Trimester (Nearing the Finish Line)

During the third trimester, Perez-Delboy says, "It's all about weight gain -- for baby and mom." As delivery day nears, you may be feeling fatigued, ungainly, and short of breath, but you may also be enjoying the beauty of your rounded belly. Meanwhile, inside that belly, your baby:

  • Is becoming "safer for the outside" with every passing day. In a high-level neonatal intensive care unit like Perez-Delboy's, a fetus born at 24 weeks has about a 50-50 chance of survival. By 28 weeks -- just four short weeks later -- about nine in every 10 babies born survive.
  • Is beginning to "practice breathe" -- not air, but amniotic fluid.
  • Is active enough that you might detect a hand, foot, or elbow poking at you through your abdomen.
  • Has grown from the size of an eggplant or large papaya at the beginning of the trimester to about the size of a small pumpkin by the time those first contractions start.

Your body's getting ready, too:

  • As the baby's head moves lower, a process called "engagement," you may be feeling more pressure on your bladder but less up near your ribs. It's a mixed blessing. You'll have to go to the bathroom more often, but breathing and eating will be easier.
  • Some women find a clear or yellowish substance known as colostrum leaking from their nipples, while others don't produce a drop until after baby is born.
  • Your weight gain is probably slowing down, but your feet and hands may look as if someone inflated them with a bike pump. This common condition, called edema, goes away quickly after birth -- but if you notice very sudden swelling, especially in your hands or face, call your doctor.

During the first few weeks of gestation, it might be hard to believe you'll ever reach the fabled 40-week mark, when you finally get to meet your baby. But after giving birth, women sometimes look back at their pregnancy with feelings of nostalgia. So enjoy these brief months when your baby lives nestled under your heart as you anticipate the moment when he's snuggled in your arms instead.

Show Sources


Annette Perez-Delboy, MD, associate professor of obstetrics and gynecology, Columbia University Medical Center, New York. 

Regan, L. I’m Pregnant: A Week-by-Week Guide from Conception to Birth, DK Publishing Inc., 2005.

Burt, C. Continuing Education in Anaesthesia, Critical Care & Pain,  2009; vol 9: pp 44-47. 

March of Dimes: "Pre-term Labor."  

American Pregnancy Association: "Swelling During Pregnancy." 

© 2011 WebMD, LLC. All rights reserved. View privacy policy and trust info