Fetus & Infant Development in the Womb

Pregnancy

• There are 40 weeks in a pregnancy, or 10 months, which can be confusing for some. There are two ages to be aware of in pregnancy; gestational age and fetal age. Gestational age is started on the first day of the mother's last menstrual period. Fetal age is the age of the fetus from the date of conception. There are 40 weeks in pregnancy according to the gestational age. For example, if you are six gestational weeks along, the fetus is actually four weeks old. Pregnancy technically begins when a sperm fertilizes an egg.

First Trimester

• The first trimester of pregnancy begins after the fertilized egg has implanted. The gender has already been determined (when the egg and the sperm met), so your little one is already a he or a she. All the body parts begin to form during this trimester, including organs. American Pregnancy says that by week six, a heartbeat may be detected through a vaginal ultrasound. By the end of the first trimester, or 12 weeks, the fetus is almost three inches long and weighs about an ounce.

Second Trimester: Part One

• The fetus is alive and kicking (literally) by the second trimester. The mom may begin to notice little flutter-like movements which is the fetus moving and kicking around in the womb. These movements are typically felt between sixteen and twenty weeks. The fetus also has developed its own set of fingerprints, fine hair called lanugo is beginning to grow all over the body and the fingernails begin to grow. Midway through the second trimester the bones of a fetus have hardened from the rubbery cartilage that they once were, according to BabyCenter.com. There are so many developments in the fetus over the second trimester.

Second Trimester: Part Two

• During this trimester is when many expectant parents find out the gender of the fetus, usually at an ultrasound between weeks 20 and 22. Week 24 marks an exciting time as the baby could be born and have a good chance of surviving with the help of serious medical intervention. They eyebrows as well as the eyelids are in place during the latter part of the second trimester. By the end of the second trimester, the fetus weighs almost two-and-a-half pounds and is more than a foot in length. Some would say that the baby is now looking pleasingly plump and looks much more like a newborn would than the fetus did at the beginning of the second trimester.

Third Trimester

• The third trimester is a time of rapid weight gain for the fetus as he puts on extra fat and grows to a newborn size. Midway through this trimester, the fetus typically moves into a head down position to prepare for birth. The fetus is getting very cramped in the womb as he rapidly grows in the small space. By the end of the third trimester, the fetus will weigh an average of eight pounds and will be 20 inches long, though this will vary greatly.