The first trimester is week 1 through week 12 of your pregnancy. Many hormonal changes are affecting almost every organ system in your body. Some of the changes that might occur are:
Good News – most of these discomforts should go away as your pregnancy progresses. Some women might not feel any discomfort at all! Each pregnancy is different. If you have been pregnant before, you may not have the same exact experience.
2 Weeks – Fertilization occurs when the sperm and egg unite in the fallopian tube to form a single cell. This cell is smaller than a grain of salt and contains all the genetic information for every detail of the newly created life. The developing embryo is still rapidly dividing as it travels down the fallopian tube to the uterus. The lining of the uterus is preparing to receive the embryo.
3 Weeks – The embryo begins to implant in the lining of the uterus. Hormones trigger the mother’s body to nurture the pregnancy and prevent her monthly periods. The baby is about the size of the “period” at the end of this sentence.
4 Weeks – The hCG hormone found in the mother’s urine at this time is used to determine pregnancy. The baby’s brain, spinal cord, and heart begin to form and arm and leg buds appear.
5 Weeks – The heart, about the size of a poppy seed, begins to beat. The first signs of brain development are evident and the foundation for every organ system is beginning to develop.
6 Weeks – The basic structure for the entire central nervous system (brain and spinal cord) has formed. The eyes are developing and the arm and leg buds are visible. An ultrasound scan can pick up the heartbeat.
7 Weeks – The baby is now making its own blood. The genitals are forming to determine whether the baby is a boy or girl.
8 Weeks – At the end of eight weeks, the baby appears more human and is nearly 1 inch long and weighs less than one-eighth ounce. Fingers and toes have begun to form. The eyes have moved forward on the face and eyelids are forming. Brain waves can be measured.
9 Weeks – The ears and nose are visible and there is pigment in the retina. The limbs and fingers are rapidly growing and the bones in the arms are beginning to calcify and harden.
10 Weeks – At this stage for the first time in development, the brain can make the muscles move on purpose. The brain is producing almost 250,000 new neurons a minute. Twenty baby teeth are forming in the gums.
11 Weeks – He or she is no longer called an embryo but is now known as a fetus, a Latin word for “young one.” The baby can now yawn and suck. The eyelids are fully formed and closed to protect the developing eyes but will open again the 28th week. The kidneys begin to produce urine. The next several weeks will show rapid growth with the baby’s weight increasing 30 times and his/her length tripling.
12 Weeks – The brain is fully formed and the baby can feel pain. Vocal chords are complete and the baby can and does sometimes cry silently. The external sex organs show if your baby is a boy or girl. An ultrasound in the second trimester or later might be able to show the baby’s sex.