Fetal development during the first trimester of pregnancy

¶ … Trimester of Pregnancy

WHEN LIFE BEGINS

School new life begins when a woman's ovum or egg unites with a man's sperm in a process called fertilization (Bennington, 2001). That new life develops in the woman's body during pregnancy, which usually takes nine calendar months. Pregnancy is also called the gestation period. The gestation period, in turn, consists of three trimesters. These trimesters consist of the different stages of the embryo or fetus' development. The first trimester covers the first 13 weeks of pregnancy or the first 12 weeks of life. The second trimester covers the 14th to the 26th weeks and the third trimester, the 27th to the 40th weeks (Bennington).

In the first month, the embryo is usually 1/8th of an inch or.275 cm long (Bennington, 2001). It weighs roughly 3 grams. A yolk sac has already formed at this early stage. In the second month, It is about an inch or 2.5 cm long. It is 8.7 grams heavy. The head, tail and the umbilical cord are formed and the sex glands determined. The limbs, toes, fingers, the skeleton and bone cells have also been formed at this stage. A distinctively human appearance develops. Facial features, the main organ systems also take shape. By the end of the eighth week, the structures of the brain, heart, liver, limbs, ears, nose and eyes evolve. This is a most critical period of development. Harmful medications, drugs and alcohol may disturb the processes of development and cause defects or snags in the embryo. And in the third month, the embryo becomes a fetus with distinctively human features. The limbs begin to move although the movements are still uncoordinated and cannot yet be felt by the mother. The fetus is now 1-3 inches long and weighs roughly an ounce. The spleen takes over the production of red blood cells from the liver. Between the ninth and the 12th months, the fetus' waste products are channeled to the mother's circulatory system through the placenta (Bennington).

New Test for Down Syndrome

Down syndrome is one of the most common birth defects, which affects one in every 600 newborns (Market Wire, 2000). An early screening test was introduced as an alternative to the currently used Triple Test. This new test can detect 90% of cases of Down syndrome 6 to 8 weeks earlier through the use of a blood test and an ultrasound examination (Market Wire).

A collaborative study was conducted by the NTD Laboratories, Huntington Station of New York; Centro Di Diagnosi Prenatale of Palermo, Italy; GeneCare Medical Genetics Center of North Carolina; and The George Washington University Medical Center (Market Wire, 2000). The new test is called Ultrascreen. Among its capabilities are an increased detection of Down syndrome, earlier reassurance to those who obtain normal results, more time and options for those who obtain risk results, and detection of Down syndrome in women who will have a miscarriage (Market Wire).

Caution Over Vitamin A Supplements

According to the Institute of Medicine, pregnant women do not need vitamin-mineral supplements unless there is a risk for nutritional deficiency (Nutrition Research Newsletter, 2000). Risks include chronic disease or abuse of drugs, alcohol or tobacco. Unnecessary or excess supplements may cause harm. Large consumptions of retinoid compounds during the first trimester have, in some cases, shown to have caused fetal craniofacial, cardiac, thymic and central nervous system abnormalities. This is called retinoic acid embryopathy (Nutrition Research Newsletter).

Published studies conducted by the American Dietetic Association showed that the average diet of pregnant women in the United States had higher intakes of Vitamin A or retinol than the recommended dietary allowance (Nutrition Research Newsletter, 2000). Physicians and dietitians recommended that pregnant women at a low nutritional risk may take Vitamin A in the form of beta carotene to reduce the risk of excessive intake. Over-the-counter vitamin-mineral supplements often lead to high levels of retinol intake (Nutrition Research Newsletter).

Stress in the First Trimester

Studies revealed that severe stress in the first trimester may prompt early delivery (Bates, 2005). Findings showed that stress transmits signals to the fetus, which produces high levels of hormones. These hormones, in turn, hasten delivery. The findings suggested the presence of a kind of "placental clock" for delivery. Tested subjects in their first trimester had highly elevated levels of stress hormones as compared with the much lower levels of subjects in their third trimester. Examples were women who were exposed to earthquakes and delivered earlier than normal schedule. Further studies on 550 pregnant women yielded consistent links between high levels of maternal cortisol and increased levels of the placenta hormone in the first trimester. Raised hormone levels not only speeds up delivery but also leads to serious consequences on the fetus' response to stimuli and, eventually, the child's response to stress (Bates).

Levels of neuropeptides increase from the mother's hypothalamic-pituitary-adrenal stress network (Bates, 2005). The placenta responds by producing circulating corticotrophin-releasing hormones. This event adversely affects the maternal stress system and blocks communication between the hypothalamus and the pituitary. The fetus appears to be quite vulnerable to stress signals. Exposure to very high levels of stress inclines the fetus to view the environment as hostile and prepares to escape the womb in response (Bates).