At fertilization the egg and the sperm exchange parts of their dna segments to create a blueprint for the next individual. Any error in this blueprint accounts for the majority of fetal loss or miscarriage. Some researchers think that up to 80% of fertilized eggs don’t "take". Of the ones that do there is still about a 10% loss rate. From this one microscopic cell that will turn into another person. 98% of newborns are completely normal. At this time the gender or sex is decided, but it will be some time before anyone will know for sure.

About a week (week 1) after fertilization the ball of cells or zygote implants into the uterus. (see #3 in the figure to the right) Within two weeks our one cell miracle is now many thousands of cells, and we call this an embryo.



This next phase begins the organ development in the embyo. This is the most critical phase for the mother to avoid environmental toxins, certain medicines, alcohol, and tobacco.

At about (5 weeks) we see a gestational sac on ultrasound.

In the beginning of the 6th week we can see a small ring called a yolk sac on ultrasound. At the end of the 6th week we can see the fetal pole and perhaps cardiac activity in the embryo.

At the (7th week) we see a well defined fetal pole and definite cardiac activity.

By the (9th week) we call this baby a fetus. At this time we can hear the heartbeat with a doptone device about 50% of the time.

At the end of the first trimester (week 12), the baby is about 3.5 inches long and weighs about 1.5 ounces. At this time the placenta is formed and is suppling the baby with oxygen from mother's blood supply, and ridding wastes through mom’s blood system.

At, (week 13) the baby is growing very quickly and can be seen moving about on ultrasound. Within the next few weeks some ultrasonographers might be able to guess at the gender. Hopefully, any morning or evening sickness from the pregnancy will start to abate.

16-20 weeks you may feel a fluttering that is the baby's movement (quickening).

20 weeks– the baby is half-way fully formed with arms, legs, abdomen, thorax, and a head. The baby is quite active now and is moving often. Your uterus or womb is about up to your umbilicus or belly button.

21 weeks your baby's eyes are still closed; movement is stronger and more pronounced. Your baby's skin is pink. It's common to notice colostrum from the breast. By now there is a darkening of the pigmented areas of the mother's body. You may find sometimes it's a little hard to breathe with more strenuous activities. As the baby and uterus grow, they are displacing organs that reside normally in the lower abdomen and pelvis.

By the 24th week the uterus is having intermittent contractions. Your baby weighs over a one and one half pound .

24 weeks we consider your baby viable. This means about half the babies born at this age do survive. Please do not plan on delivering this early if you can help it as you are just now leaving the second trimester and heading into the last one.

26 to 28 weeks the lungs are maturing, the baby is starting to store fat in the subcutaneous layer of the skin, and hair is growing. Your baby at 28 weeks is about 15 inches long and weighs almost 3 pounds. Your baby's eyelashes, fingernails, and hair are all growing. The eyes can open and your baby becomes increasingly more responsive to the world outside the womb. Continue to talk to your baby. Many moms perceive the baby having intermittent hiccups beginning about this time.

32 to 33 weeks your baby weighs about 4 1/2 pounds and is about 16-17 inches long. Your baby's fat deposits are starting to fill out.

At about 34 weeks your baby's lungs start to work well. At 34 weeks or beyond, we usually do not give steroids if we anticipate a preterm birth. Your baby is exhibiting activities we associate with full term babies, like grabbing and sucking reflexes. If you have not begun your search for a pediatrician, please do so. Your baby may be running out of room but each and every day you should feel movement, please call us if you do not.

From 36 weeks on we consider your baby fully developed although there are organs like the nervous system which continue developing until about age 4. Many babies can still have some minor trouble with jaundice, temperature regulation and feeding, but most do just fine. Your baby will look just like a baby now. Your baby!