KTVN Channel 2 - Reno Tahoe News Weather, Video - What happens during each trimester of pregnancy

Your unborn baby develops rapidly throughout pregnancy. A cluster of cells forms when the sperm fertilizes the egg. By the fifth week of pregnancy, the fetus's heart will begin to beat. In the middle of the second trimester, your baby will be able to suck his or her thumb. After a mere 40 weeks, you'll have a precious newborn to hold in your arms.

While the transformation from cells to fetus to newborn is indeed amazing, your own body will also undergo some changes.  

The stages of pregnancy

Pregnancy is broken into three stages called trimesters. Each trimester lasts 13-plus weeks:

• First trimester: Weeks 0 (from the first day of your last menstrual period) to 13
• Second trimester: Weeks 14 to 27
• Third trimester: Weeks 28 to 40

What happens during each trimester?

Here is a snapshot of how your baby develops and how your body changes during each trimester of pregnancy.

First trimester (Weeks 0 to 13)

What happens to baby:

• The sperm fertilizes the egg in the fallopian tube. The fertilized egg moves down the fallopian tube and attaches to the uterine wall.
• All of the major organs and body structures - including the brain, heart, spinal cord and intestines - start to develop during the first half of this trimester.
• Bones and muscles start to form. Muscles can contract and your baby can make a fist.
• The baby weighs about one ounce and is about three inches long at the end of this stage.

What happens to you: Pregnancy-related hormone changes will start to affect your entire body. You may feel the effects of these changes before you even know you're pregnant. Some women experience the following conditions during the first trimester of pregnancy. But some women feel none at all:

• Morning sickness
• Weight gain
• Exhaustion
• Breast swelling and soreness
• Cravings for certain foods or aversion to foods you usually like
• Mood swings
• Headaches
• Need to urinate more frequently
• Constipation

Second trimester (Weeks 14 to 27)

What happens to baby:

• By the start of the second trimester, sex organs form. Your doctor may be able to tell if your baby is a boy or girl by now.
• The placenta finishes developing.
• The eyebrows, eyelashes and fingernails form. Your baby has his or her own unique fingerprint.
• Your unborn baby can swallow, hear and suck his or her thumb.
• The baby's body will be wrinkly and covered by a wax-like substance (vernix) and thin hair (lanugo). The baby's real hair will start to grow by the end of this trimester.
• In girls, all of the eggs will develop in her ovaries. In boys, the testicles will drop down from the abdomen into the scrotum.
• Your baby will start a regular sleep and wake cycle. He or she will be active during hours spent awake. You should be able to feel him or her move around and kick by the middle of the second trimester (at about 20 weeks).
• The baby weighs a little over two pounds and is about 14 inches long.

What happens to you: By now, morning sickness and fatigue have often subsided. This is when you start "looking pregnant" as a result of your growing baby. You may experience the following discomforts as your body expands:

• Body aches, especially in your back and abdomen
• Stretch marks
• Dry, itchy stomach
• Tingly or numb hands
• Slight swelling in your feet, fingers and face (if swelling comes on quickly, call your doctor because this could be a sign of preeclampsia)
• A dark line running from your belly button to your pubic line, called the linea nigra

Third trimester (Weeks 28 to 40)

What happens to baby:

• Your baby grows the most during the third trimester.
• The baby opens his or her eyes for the first time since the end of the first trimester. He or she can even notice changes in light.
• The lanugo starts falling off at the start of this trimester. The skin will be less wrinkled.
• The baby will likely descend down the uterus into the heads-down position to get ready for delivery.
• Your baby's taste buds will form and he or she will be able to tell the difference between sweet and sour tastes. The baby may even hiccup.
• All organs will be fully developed by the end of the third trimester.
• At birth, your baby will be around 20 inches long and weigh between six and nine pounds. But healthy babies can come in all shapes and sizes.

What happens to you: You may be the most uncomfortable during the final stage of pregnancy. Because of your size, you may find it hard to get comfortable and sleep at night. In addition to what you felt during the second trimester, you may also experience:

• Heartburn
• Shortness of breath
• Pre-milk called colostrum leaking from your nipples
• Contractions that may signal real or false labor