By Brandi M. Seals
During pregnancy the fetus grows at alarming rate. The zygote (fertilized egg) starts out small then the size of a pin head and develops within 38 weeks into a fully matured fetus generally weighing a little over 7 pounds.
Mothers give birth generally during the weeks 38 through 40. But if you thought that meant 38 to 40 weeks after conception, you were wrong. When the egg becomes fertilized the unborn child is already 2 weeks old. Pregnancy is counted from the first day of the mother's last period.
During fertilization the sperm and the egg join together in the fallopian tube and form a zygote. The unborn baby is considered a zygote until it reaches the uterus in the next 3 to 4 days. The baby's physical characteristics will be determined by 46 chromosomes. 23 chromosomes come from the father and 23 chromosomes come from the mother.
In week three the developing embryo is looking to implant in the uterus. The embryo is more than just a group of cells at this point. The beginnings of the central nervous system, backbone, kidneys, liver, intestines and spinal column have begun to develop. The heart has also begun to form.
The mother's menstrual cycle stops due to hormones released by the embryo. The embryo implants and upon doing so the placenta begins to form.
A lot is currently underway. The embryo's heart will begin beating by day 21. The brain has developed into 5 areas. Arm and leg buds are starting to form and the facial features, such as eyes, lips, and nose, have begun to take shape. The embryo appears to have a tail as the spinal cord grows faster than the rest of the body. Do not worry; this will disappear as the embryo continues to grow.
Despite all of the development, the embryo is quite small. In fact, it measures about 1/5 of an inch in length.
The changes inside the embryo continue. The major organs have begun to form. The embryo now has its own unique blood type. Knees and elbows are forming as are hair follicles and nipples. The eyes are developing and have a retina and lens. The muscle system is developed and the embryo can move.
The embryo is able to swim and move in its amniotic sac. Hands and feet have developed. At the end of week 8 the embryo becomes a fetus.
The heart is nearly completed and its beat can be heard through the use of machines at the doctor's office. The baby's face is pretty much formed and the eyes are almost fully developed. During this stage the eyelids will close and they will not reopen until week 28. Fingers and toes are fully formed. Nails and earlobes will begin to grown. The embryo is about 1 inch in length.
The brain is developed. Muscles tissue lengthens and bones become harder. The fetus begins to grow eyebrows and eyelashes. It also becomes active. It can kick, move around and even somersault. The fetus is approximately 3 inches long and weighs nearly an ounce. Perhaps most excitingly, this is when the sex organs form.
The fetus is about 5 inches long and has begun to grow hair on the head and the rest of the body.
This is when the mother can generally start to feel the fetus move. A fine hair covers the entire body. The fetus can hear and recognize its mother's voice. Now is the time to schedule an ultrasound as the sex organs will now be visible.
The fetus has started to gain weight and should weigh around 1/2 a pound. The fetus has also grown and is about 10 inches from head to toe. The fetus' skin is no longer transparent. It has turned opaque.
The fetus' unique footprints and fingerprints are forming. The fetus begins practicing breathing by inhaling amniotic fluid into the developing lungs.
Weeks 25 - 28
The brain develops rapidly and the nervous system is now able to control some body functions. Babies born this early do have a chance at survival and a fetus is considered legally viable at 28 weeks.
Weeks 29 - 32
The fetus begins to gain weight rapidly.
Weeks 38 - 40
The fetus is now at full-term and can be born any day now.