Fetal Development in the First Trimester Chrystal DeCoste

Week 1 & 2 The first week of your pregnancy is actually the week you started your last period. As a result, the baby's age is two weeks behind the gestational age. During the second week, estrogen triggers your uterus to form a lush, blood-rich lining of tissue. Rising levels of the hormone progesterone prepare the uterus to support a fertilized egg. At the same time, the ovaries ripen eggs in fluid-filled sacs called follicles. It's during this brief period that your body's preparation can result in conception once sperm meets the egg.

Week 3 By the third week, things really do start to happen baby-wise. Around mid-cycle (day 14 of a typical 28-day cycle), you ovulate-one of your eggs is swept into your Fallopian tube. In the next 12 to 24 hours that egg can be fertilized, if one of the 350 million sperm manages to trek all the way to the Fallopian tube--from the vagina through the uterus--to penetrate the egg.

Fertilization When life begins. When sperm and ovum meet to form a single cell, new life is created. A fertilized egg is called a zygote. It begins dividing into identical cells as it sails down the Fallopian tube to the uterus, where it will continue to grow. All characteristics (sex, eye color, shoe size, intelligence, etc.), is determined at fertilization by the baby’s genetic code. Life truly begins at fertilization,this is when the sperm and the ovum meet to form a single cell, a new human life is created. All characteristics of each person - sex, eye color, shoe size, intelligence, etc. - are determined at fertilization by the baby's genetic code in the 46 human chromosomes. Every person begins as a separate single cell; nothing new is added but oxygen and nutrition. If the process is not interrupted, a human being will live about nine months in the mother's uterus and decades outside it. That person has never existed before and will never exist again. This photograph was taken about 30 hours after fertilization. Within one week of fertilization, a new human being implants in the mother's uterus and is nourished there.

Week 4 The cells of your fertilized egg, now called a blastocyst, are multiplying. Once down the Fallopian tube, it nests in the uterus, where it divides into two parts. The half attached to the uterine wall becomes the placenta, the support system that nourishes the developing life. The other half will become the baby.

Week 4 cont’ Nerve growth begins when a sheet of cells on the back of the embryo folds in the middle to form a tube, which will become the spinal cord. At one end, the tube enlarges to form the brain's major sections. What will become amniotic fluid begins to collect now. In the weeks and months ahead this fluid will cushion the fetus. By the end of the first month, the embryo is about 1/10 of an inch long. The heart, no larger than a poppy seed, has begun beating.

6 weeks Around week six, the embryo has the beginnings of a mouth and digestive system. A simple brain spine and central nervous system. Pits have formed which will become the baby’s eyes and ears.

6 weeks cont’ The baby has brain waves that can be measured with an electroencephalogram. Stomach and chest are also developing and the heart begins as a bulge in the chest and will begin beating by the end of the week. Limb buds have developed as well as a systems of blood vessels.

7 weeks The baby is already kicking. The unborn baby swims freely in the amniotic sac with a natural swimmers stroke. Although the baby is moving, the mother does not begin to feel the baby until 4 1/2 months.

9 weeks The baby is now extremely active. At this stage, it is commonplace for parents to watch their child moving around in the uterus through ultrasound pictures. The baby begins swallowing amniotic fluid as early as this stage.

10 weeks The baby is now sensitive to touch. The baby can also “breathe” amniotic fluid and urinate. At this age, he or she will seize an object placed in the hand.

11 weeks All organ systems are now functioning. These tiny human feet are perfectly shaped, and could stand on an adult’s fingernail. The baby also has eyelids, nails, and fingerprints.

From this age on, there is only growth in size and maturation of the organs already present. All organ systems are functioning. The baby has a skeletal structure, nerves, and circulation.

12 weeks At this age, the heart pumps several quarts of blood through the body every day. At this point, the baby has developed the body parts required to experience pain, including all of the nerves, spinal cord and thalamus.

By the end of this trimester, your baby will weigh approximately 1 ounce, and be about 3 inches in length. By the end of this trimester, your baby's fingers and toes are close to being fully formed. The facial features are becoming well defined, with an obvious chin, nose, and forehead. Eyes are fully formed and eyelids are developing. If you were to have an ultrasound now, you would be able to see fetal movements, although you will not feel these for at least another month.

References http://www.clicked.com/babytime/trimester1.html#fetus http://babyzone.com/stage.htm http://www.carnationbaby.com/P/Pc.html

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