1 Week of Pregnancy

Baby's Growth and Development at Week One

It may seem strange, but your pregnancy journey begins before your baby even is conceived.

The first week of pregnancy actually begins with the start of your last menstrual period. Why? It's hard to pinpoint exactly when your egg becomes fertilized, but the date of your last cycle is a more accurate starting point. Your doctor will calculate your due date by counting 40 weeks from the start of your last menstrual period.

It's called the Gestational Age, and it's how most doctors measure pregnancies. Because ovulation and conception take place about two weeks after your period begins, your baby's Fetal Age (which begins when your egg is fertilized) will be two weeks less than his Gestational Age. So, when you're 8 weeks pregnant, your baby's fetal age is 6 weeks.

5 Week of Pregnancy

Baby's Growth and Development at 5 Week Pregnant

After weeks of rapid cell development, your baby takes on a more distinct form. During the fifth week of pregnancy, here's what's happening inside:

• Her heart and circulatory system take shape — a bulge indicates where your baby's heart is developing. By the end of the 5^th week of pregnancy, your baby's earliest blood vessels form.
• Around the 5^th week of pregnancy, your baby's heart begins to beat and may be visible on an ultrasound.
• The umbilical cord replaces the yolk sac. The umbilical cord works with the placenta to bring nutrition and oxygen to your baby and remove waste.
• At 5 weeks pregnant, your baby is the length of the tip of a pen, about 1/17 inches, and growing rapidly every day.

10 Week of Pregnancy

Baby's Growth Development at 10 Week Pregnant

It's official! After weeks of life as an embryo, by the end of the 10th week of your pregnancy, your baby becomes a fetus*. Here are some of the other changes your baby is going through during your 10th week of pregnancy:

• By the 10th week of pregnancy, your baby measures more than one inch, or roughly the length of a quarter. By the end of the 1st trimester, your baby will grow to be about 3 inches — around the length of a kiwi fruit. This measurement doesn't even take into account arms and legs. That's because in the 1st trimester, your baby is measured from the top of the head to the bottom of the rump.
• By the beginning of the 10th week of pregnancy, all of your baby's vital organs have formed.
• His embryonic tail, located at the bottom of his spinal cord, has disappeared.
• His bones continue to develop. On an ultrasound, your baby's bones appear white.
• At 10 weeks pregnant, his ears get close to their final form.
• His teeth buds emerge and his eyelids develop further.
• His testes start producing the male hormone testosterone around the 10th week of pregnancy.
• Tiny fingers and toes are fully separated (no more webbing).

15 Week of Pregnancy

Baby's Growth and Development at 15 Week Pregnant

Your baby's internal and external growth continue at a remarkable pace throughout the 15th week of pregnancy.

• When you're 15 weeks pregnant, your baby is about 4 1/2 inches from head to rump, and weighs about 2 to 3 ounces. She’s about the length of a large apple.
• Your baby's hair might appear on her scalp and eyebrows. Hair follicles even begin to generate the pigments that give hair its color.
• By your 15th week of pregnancy, your baby's ears probably have reached their permanent position on the side of her head, and her eyes are moving to where they belong on the front of her face.
• Your baby's skin is developing, but remains extremely thin.
• Your baby's skeletal system and muscles further develop and strengthen.
• By the end of your 15th week of pregnancy, your baby might be able to wiggle fingers and toes, make a fist, or even suck her thumb!

20th Week of Pregnancy

Baby's Growth and Development at 20 Weeks Pregnant
When you're 20 weeks pregnant, your baby is getting used to all his developing parts. Your baby is moving around and you may be able to feel it. Baby development includes:

• When you're 20 weeks pregnant, your baby measures about 6 inches, about the length of an eggplant, and weighs about half a pound.
• Your baby's skin thickens and develops layers under the vernix during the 20th week of pregnancy.
• His hair and nails continue to grow.
• His limbs are well developed when you’re 20 weeks pregnant.
• Your baby is moving and you can feel it. Make a note of when you felt these movements start and let your doctor know.

25th Week of Pregnancy

Baby's Growth and Development at 25 week Pregnant

During the 25th week of pregnancy, your baby uses her tiny developing hands to learn about herself and her environment. Here's what else is going on:

• This week, your baby weighs about a pound and a half, and is about the length of a small cantaloupe.
• Reach for the stars! When you're 25 weeks pregnant, your baby's hands are fully developed. She even can make a fist.
• The nerve connections in her hands continue to develop.
• She uses her hands to explore her environment.

30th Week of Pregnancy

Baby's Growth and Development When You are 30 Week Pregnant

During this 30th week of pregnancy, your baby continues to steadily add weight and important, insulating layers of fat to his body.

• At 30 weeks of pregnancy, your baby weighs about 3 pounds and is about 10 1/2 inches long from crown to rump, or about the length of a bunch of celery. (His legs and feet increase this measurement by many more inches.)
• From this week until week 37 of pregnancy, your baby gains an impressive half a pound a week!
• Your baby might be practicing breathing movements as he rhythmically moves his diaphragm. You even might notice a slight twitching in your abdomen when this happens.
• Your baby's brain continues to expand and develop, creating additional grooves and folds in the brain's surface. These wrinkles give your baby's brain tissue the needed room to expand as he develops and learns throughout his lifetime.
• Your baby's brain can now regulate his temperature, so he begins to lose the lanugo — fine hair that has been covering his body for warmth.