Day 1: It might seem strange, but you're not actually pregnant the first week or two of the time allotted to your pregnancy. Yes, you read that correctly! Conception typically occurs about two weeks after your last period begins. To calculate your due date, your health care provider will count ahead 40 weeks from the start of your last period. This means your period is counted as part of your pregnancy — even though you weren't pregnant at the time.
Week 5: The fifth week of pregnancy, (3rd week after conception), is when the baby's brain, spinal cord, heart and other organs begin to form. The
heart, which is still outside the baby's body, begins to beat at regular a rhythm. Eye spots, arm and leg buds are also visible even though the baby is only about 1/4 of an inch long.
Week 7: Seven weeks into your pregnancy, (5th week after conception), your baby's brain and face are rapidly developing. Tiny nostrils become visible, and the eye lenses begin to form. The arm buds that sprouted last week now take on the shape of paddles.
Week 16: The baby now measures about 4.3 to 4.6 inches and weighs about 3.5 ounces. You should be able to feel the top of your uterus about 3 inches below your belly button. The baby's eyes can blink and the heart and blood vessels are fully formed. The baby's fingers and toes have fingerprints.
Week 21: The baby weighs about 10 ounces and is a little more than 6 inches long. Your uterus should be at the level of your belly button. The baby can suck a thumb, yawn, stretch, and make faces. Soon -- if you haven't already -- you'll feel your baby move, which is called "quickening."
*Cunningham G, et al. Williams Obstetrics. 21st ed. New York: McGraw-Hill Publishers; 2001.