Over the course of nine months the beginnings of a new human life starts as a singled celled zygote that with nourishment, care and an ideal set of various factors develops into a complex system of cells that allows for the fetus to maintain homeostasis and function in the world independent from it’s prenatal life source. The fetus transitions through three distinct periods of prenatal development, germinal, embryonic, and fetal arriving at the end of the third trimester with organized systems that allows for regulated functioning. During the course of prenatal periods the introduction of teratogens has the potential to disrupt the natural course of progress, factors associated with the impact of teratogens on the developing fetus include timing, frequency of exposure and additive impact, and the health of the mother during the course of pregnancy.
The germinal stage of pregnancy occurs begins with fertilization (day 0) and continues through the second week. In that time the one-celled zygote travels slowly down the fallopian tube towards the uterus while multiplying and dividing (Berger, 2012, p. 90). Cells begin to differentiate into the placenta and the early embryonic mass and prepare to take on various functions. While that occurs, the first task at hand for the blastocyst is implanting itself to the uterine wall where it will take root and continue it’s development.
Days 14 through 56 constitute the embryonic stage of development, beginning with implantation. It is in this stage that the most rapid prenatal changes occur as the embryo lays the groundwork for the complex systems it will come to develop (Berk, 2012, 98). It is for this reason that during this stage of pregnancy the embryo is most susceptible to the various teratogens, ranging from maternal illness, drugs, and various other toxins, that find their way across the placenta (Weng, Odouli, & Li, 2008). The first weeks of this period begin with the development of three distinct layers of the embryo, the ectoderm, mesoderm and endoderm which will develop into the nervous system and skin, the musculoskeletal system, and the digestive, excretory and respiratory systems respectively (Berk, 2012, p. 99). The central nervous system begins its advancement with the appearance of the neural tube that will develop in to the brain and spinal column (Berger, 2012, p. 91), and the heart begins to beat though at an imperceptible flutter (Moore & Persaud, 2008). Facial features begin to appear, as do the extremities, and digits. The embryonic period is distinct in that all major body systems have taken root and continue to develop over the course of weeks, at the end of which the embryo is roughly one inch long and weighs 1 gram (Berger, 2012, p. 100).
The germinal and embryonic periods are both within the first trimester of pregnancy, the second and third trimester both make up the final period of prenatal development, the fetal stage. The period of the fetus begins in the 9th week of gestation and last until the birth of the fetus in ideally between the 37th and 42nd week of gestation. Fetal growth slows and continues in a cephalocaudal (head to tail) and proximodistal (center and out) manner, and at 12 weeks a gender distinction can be made (Simkin, 2008). By birth the head will make up half of the newborns birth weight. As the framework has already been set in place, the purpose of the fetal period is about fine-tuning the details, the digestive and excretory systems develop, teeth buds and hair appears and eye movement can be monitored (Berk, 2012, p. 100).Research has shown that during this stage, as brain capacity develops, the fetus becomes conscious of it’s environment and develops things such as preference to taste and sound, the ability to feel pain, and the ability to remember various stimuli (Lee et al., 2005). The neurological, respiratory and cardiovascular systems continue to become more sophisticated during this time period, and when all three of...
References: Berger, K. S. (2012). The developing person through the life span. New York, NY: Worth Publishers.
Berk, L. E. (2012). Infants and children: Prenatal through middle childhood. Boston, MA: Pearson Publishers.
Lee, S. J., Ralston, H. J., Partridge, J. C., & Rosen, M. A. (2005). Fetal pain: A systematic multidisciplinary review of the evidence. Journal of American Medical Association, 294, 947-954.
Moore, K. L. & Persaud, T. V. N. (2008). Before we are born (7th ed). Philadelphia, PA: Saunders.
Simkin, P. (2008). The birth partner: A complete guide to childbirth for dads, doulas, and all other labor companions (3rd ed). Boston, MA: Harvard Common Press.
Weng, X., Odouli, R., & Li, D. K. (2008). Maternal caffeine consumption during pregnancy and the risk of miscarriage: A prospective cohort study. American Journal of Obstetrics and Gynecology, 198, 279-287.
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