How Big is My Baby?

From Cells to Baby

During the nine months of pregnancy, your baby grows from an embryo the size of a few cells into an infant who will weigh between 6 to 10 pounds at birth.

Pregnancy can be a surreal experience. Your body is changing, and you can feel a little person growing inside you. You see an image of your baby during your ultrasound, but, in reality, everything is happening out of your sight. Until you meet your baby for the first time, this sense of mystery may make you feel as though you aren't really pregnant. Rest assured though: While morning sickness is raging, you're tossing and turning at night, and you're feeling your baby's kicks, he's growing and developing from a clump of cells into a baby ready to meet the world.

Early Pregnancy

The first 12 weeks of pregnancy are called the first trimester. This can be the time that pregnancy may feel the most surreal because the baby is only just starting to make her presence felt. If not for the nausea, exhaustion and mood swings, you might not even know you were pregnant. A lot is going on inside of you, though. By the end of the first trimester, your baby will have grown from an embryo until she is about 3 inches long and weighs about an ounce. Her heart started to beat regularly at around 8 weeks. All of her major organs are in place and developing by the end of those first three months, and your baby has tiny fingers, toes and eyelids. Her muscles and nerves start to become coordinated, and she can make a fist and move her limbs, although you probably won't feel it yet.

Growing and Developing

The second trimester covers weeks 13 to 28 and encompasses a great deal of growth and development. Major second trimester milestones include the emergence of the sucking reflex at about 16 weeks and more advanced lung formation at about 24 weeks. At 20 weeks, or the halfway mark, your baby is about 6 inches long, and he weighs approximately 9 ounces. By the end of the second trimester, you are probably feeling your baby start to kick and turn. He becomes easier to feel because he has grown to be about 12 inches long and weighs a whopping 20 ounces. After about 23 weeks, your baby is considered viable, meaning that with intensive care, he has a good chance of surviving outside of your womb. Of course, it is much better for him to stay inside and keep growing for another few months.

Getting Bigger and Bigger

The third trimester extends from week 29 through 40, and it's the time when your baby gets ready to meet the outside world. By the end of week 32, she weighs about 4 pounds, and by week 40, your baby is full sized. She could weigh from 6 to 10 pounds and is 19 to 21 inches long. Your baby's bones are soft but fully formed by week 32, and she starts to practice breathing. Those kicks and stretches will feel more defined as she grows and runs out of room to move inside you. By 39 weeks, your baby is considered full term and ready to meet the world. As you get closer to your due date, she will start to turn into a head-down position to get ready for birth.

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