Fetal Development Trimester to Trimester

Pregnancy is a stage in a woman's life lasting 9 months, equivalent to 3 trimesters, or 40 weeks, or 280 days counting from the first day of her last menstrual period. Hence, your first trimester of pregnancy lasts from week 1 to week 13; the second trimester goes from week 14 to week 27; and the third and last from week 28 to week 40 or until birth, since labor or delivery may occur before or after.

When it comes to talking about fetal development, we are speaking of the embryo becoming the fetus that will be delivered as your newborn baby. Every trimester has particular milestones in this development. The first trimester is when you will hear the baby's heartbeat for the first time. During the second trimester, the baby moves for the first time, while in the third trimester, many pregnant women may experience Braxton Hicks contractions preparing the body for labor.

To ensure the correct fetal development, some tests are done during the first trimester, including the chorionic villus sampling. The second trimester is the time for amniocentesis, a diagnostic test, and the Rhesus incompatibility that scans the mother and the baby's blood searching for their Rh factor. While the third trimester is usually intended to find certain problems in the mother, such as gestational diabetes, which can prevent further development and harm to the baby.

Fetal development begins around week 6 during the first trimester, when the embryo is about 1/5 of an inch in length, and the baby's heart is beating. Mouth, head, liver, and intestines begin to take shape until week 10 when the embryo is about 1 inch in length and the facial features, fingers hands, feet, toes and limbs become apparent, while many of the embryo internal organs begin to function and the nervous system is responsive.

During the second trimester, the embryo is now a 3 inches long fetus that weighs almost an ounce, while sex organs and muscles begin to form and develop. Fingernails, toenails and eyelids also form, and the baby's spontaneous movements can be clearly observed. By week 18, the fetus is about 5 inches long. Baby grasps, blinks, and moves the mouth, while hair grows on the head and body.

By the end of the second trimester, the fetus is about 10 inches from head to toe and weighs near 1/2 a pound. The baby's external skin turns from transparent to opaque and sweat glands develop.

Starting the third Trimester, the fetus can inhale, exhale and even cry. The baby's tongue develops taste buds and the eyes are formed completely. At this stage, the fetus has over 50% chances of surviving outside the womb under intensive medical care. By week 30, the fetus is now capable of living outside the womb in case of premature birth; otherwise, it develops until week 40 when the normal gestational period ends.