Fertilization starts in the fallopian tube, and it occurs when the man’s sperm reaches the egg of the female and penetrates it. The sperm and the egg merge and form a tiny single-celled organism called a zygote. The zygote is made up of the 23 chromosomes from the man’s sperm and the 23 chromosomes from the female’s egg. These chromosomes are the ones that determine the baby’s hair color, eye color and sex (Watson, undated, First Trimester: From Conception to Embryo). After fertilization, the zygote journeys through the fallopian tube to the uterus. It is during this journey that the zygote divides.
The zygote continues to divide until it has gone from one cell to 100 cells, and then forms into what is called a blastocyst (Watson, undated, First Trimester: From Conception to Embryo). A blastocyst is where the first cavity appears, pushing cells to either outside or inside, and as it falls — floating through the fallopian tube — about 70-75% will implant in the uterine wall (The Visible Embryo, undated). The inner group of cells will form the embryo, while the outer group forms the placenta, which will provide nourishment to the fetus (Watson, undated, First Trimester: From Conception to Embryo).
First Trimester Weeks 1 to 4 Three weeks after conception, the blastocyst implants itself into the mother’s uterine wall and releases hCG — human chorionic gonadotropin (Watson, undated, First Trimester: From Conception to Embryo). By the end of the first month of pregnancy, the baby (two-weeks old if counted from conception), looks like a tiny, tadpole-shaped embryo, smaller than a grain of rice. There is now a head – with a mouth opening – a primitive heart that begins to pump, and a rudimentary brain (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 109). Weeks 5 to 8
By the fifth week, aside from the brain and heart, the baby’s spinal cord and other organs begin to form. The embryo is now made up of three layers — the ectoderm, mesoderm, and endoderm – from which every organ and tissue will form. From the ectoderm, the nervous system and backbone will develop; from the mesoderm, the heart and circulatory system; and from the endoderm, the lungs, thyroid, gastrointestinal tract, liver and pancreas. The placenta has started to form, as well as the umbilical cord, which delivers nutrients to and removes wastes from the embryo (Watson, undated, First Trimester: From Conception to Embryo).
Moreover, at this stage, the embryo is about one-inch long, and its tail gone. By the end of the second month, arms and feet – complete with fingers and toes – have formed from tiny buds, along with eyes, ears, a nose tip, and a tongue. The embryo now makes spontaneous movements, too (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 134). It is around the 8th week that the embryo becomes a fetus. This is also the stage where the external genitalia are formed (Watson, undated, First Trimester: From Embryo to Fetus). Weeks 9 to 13
This is the last month of the first trimester. The fetus can now reach 2 ? to 3 inches in length and weighs 1 ? ounces. It is now about the size of an apple. The head – which now sit1s on a neck – is still disproportionately large. The eyes are now moving closer together and the ears are on the sides of the head. Moreover, fingers and toes now have soft nails, and the hands have become more functional. Inside the fetus’s mouth, taste buds have developed, as well as the sucking reflex, and twenty buds that will become baby teeth in the future have formed.
The baby makes urine and excretes it in the amniotic fluid. The external genetalia are now well-developed enough to be able to detect the baby’s sex by ultrasound. The heartbeat can now be heard with a Doppler (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 155). Possible complications during first trimester The mother needs to be extra careful during the first trimester when the formation of the delicate organs takes place (Watson, undated, First Trimester: From Embryo to Fetus). Around one out of eight known pregnancies is lost in the first trimester.
In fact, this number is an underestimate, since some women miscarry before they even know they are pregnant, and interpret the bleeding as menstrual period (Greenfield, 2004) . Ectopic pregnancies also occur during the first trimester. Signs of an ectopic pregnancy are sharp, abdominal cramping or searing pain on one side, depending on the fallopian tube involved (Rosenthal, 1998, Introduction section). It happens when an embryo is implanted outside the uterus, usually in the fallopian tubes. This usually occurs because some irregularity in the tube blocks the passage of the egg down to the uterus.
In rare occasions, the fertilized egg gets implanted in the ovary, the abdominal cavity, or the cervix (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 124). Ectopic pregnancies have become more common after the results of sexually transmitted diseases, pelvic inflammatory disease, and assisted reproductive technology started to factor into the childbearing population (Rosenthal, 1998, Introduction section). Moreover, women who contract chicken pox between the second and fourth month of pregnancy have a slightly higher rate of miscarriage and have a slightly higher rate of delivering babies with birth defects (Gliksman, M. & DiGeronimo, T. , 1999, p. 97).
Since this trimester is when organ formation occurs, exposure to teratogens can cause serious problems. A teratogen is a chemical, medication, infectious disease, or environmental agent that might interfere with a fetus’ normal development and result in miscarriage, birth defect, or complication during pregnancy (Mother & Child Glossary, undated). Second Trimester Weeks 14 to 17 The fetus is now about 5 inches long and weighs about five ounces, with the body growing faster than the head and reaching more realistic proportions.
Fingerprints and toeprints have developed, and temporary hair – lanugo – has appeared on the body. The baby can now suck its thumb, swallow amniotic fluid, which is passed as urine, and do practice breathing movements. The placenta is now fully functional. A baby girl’s uterus is formed and the ovaries equipped with primitive egg cells. The baby’s bones are harder and it can already move its arms and legs (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 173). Moreover, blood vessels can easily be seen through the skin, which is still thin and translucent.
The fetus can also make a fist, open its mouth, and move its lips. The heart is beating 117 to 157 times per minute, the stomach is producing digestive juices, and the kidneys are producing urine. White fatty material also begins to enclose the nerve fibers of the spinal cord, and the hearing starts to develop, enabling the baby to hear internal-organ and outside-world sounds (Gliksman, M. & DiGeronimo, T. , 1999, pp. 108-109). Weeks 18 to 22 At this time, the skeleton can be clearly outlined on x-rays of the fetus. Ears stand out from the head, and lanugo covers the entire body (Gliksman, M. & DiGeronimo, T. , 1999, p. 109).
The baby’s digestive system now produces meconium – a black, tar-like substance that will make up its first few bowel movements. The fetus is also coated in a white greasy substance called vernix caseosa, which protects its skin from the amniotic fluid in utero (Watson, undated, Second Trimester: Halfway There). At the end of the fifth month, the baby is about 7 to 9 inches long, and weighs nearly a pound. As muscles strengthen, nerve networks expand, and the fetus is much more active and coordinated – capable of certain movements that help the baby grow and develop motor skills.
The baby, moreover, has regular periods of sleep and wakefulness, and is capable of various facial expressions. A baby boy’s testicles have started their descent from the abdominal cavity into the scrotum (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 205). Weeks 23 to 27 At this stage, the baby’s eyebrows and eyelashes are forming; lips are getting more distinct; eyes are becoming more developed, but still lack color; and the first signs of teeth appear beneath the gum line. Blood vessels in the lung are also developing (Gliksman, M. & DiGeronimo, T. , 1999, p. 130).
Moreover, the baby is over a foot long and weighs close to 2 pounds. The fetus is still quite active and even more coordinated in its movements and has developed a strong grip. The baby’s eyes can open and close and can already react to light. Vocal cords are functioning, although the baby won’t make a sound until the first cry after birth. Hiccups, however, are common and may shake baby’s uterine home often. A baby born at this stage can now survive, but with intensive care (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 240).
Possible complications during first trimester After the first trimester, the risks of miscarriage lessen, although not eliminated. Later miscarriages may be caused by an abnormality or infection in the uterus or in the placenta, or a weak cervix. An incompetent cervix is a cervix that is softer and weaker than the normal ones. It may shorten and dilate as the weight of a growing baby puts pressure on it, causing second trimester miscarriage, premature rupture of the fetal membranes, or pre-term delivery.
Another second trimester complication is placenta abruption, where the placenta separates prematurely from the uterus (Second Trimester Complications that May Cause Miscarriage, 2001). Third Trimester Weeks 28 to 31 The baby is gaining weight rapidly as more fat is deposited under the skin. By the end of this month, the baby will weigh in at about 3 pounds and measure about 16 inches long. Lanugo has started to disappear and head hair starts to grow. Nails have reached the top of fingers and toes, and the skin is pink and smooth.
Brain growth in this trimester will be dramatic, and will continue in the first two years of life. The lungs, though still immature, are beginning to function (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 261). Weeks 32 to 35 The fetus is now about 18 to 20 inches and 5 to 6 pounds, gains at a rate of ? ounce a day; looks plump and less wrinkly now as fat deposits fill out its adorable form; creases have formed around the wrists and neck. The fetus will now have regular periods of REM. The lungs are approaching maturity (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 285).
Weeks 36 to 40 More fat layers are now added to help control the baby’s body temperature after birth. At week 38, the baby is already “full term,” which means that if born at this time, it is considered a full-grown baby. All organs are now ready to function outside the womb, and the lungs are fully developed (Gliksman, M. & DiGeronimo, T. , 1999, pp. 167-168). Most babies have already settled into a head-down birthing position by the end of the third trimester.
The umbilical cord has now grown to over 2 feet in length and the placenta weighs in at about a pound a half (Murkoff, H. , Eisenberg, A. , & Hathaway, S. , 2002, p. 317). Possible complications during first trimester Certain complications can occur in the third trimester, like placenta praevia (the placenta is implanted low down in the uterus and lies over/near the mouth of the uterus. It is in front of the presenting part of the baby and can cause life-threatening bleeding), abruptio placentae (involves the detachment of the placenta from the wall of the uterus.
The blood clot is formed between the placenta and uterus) and Pre-eclampsia/eclampsia (hypertension with protein in the urine with or without oedema after 20 weeks of pregnancy is known as pre-eclampsia. Eclampsia is pre-eclampsia with convulsions, which are not due to co-incidental nervous system disease) (Complications in the Third Trimester, undated).
References Complications in the Third Trimester. Retrieved May 3, 2008, fromPlan a Baby Web site: http://www. planababy. com/COMPLICATION%203rd%20TRIMISTER. HTM Gliksman, M. & DiGeronimo, T. (1999). The Complete Idiot’s Guide to Pregnancy and Childbirth.
New York: Macmillan Publishing. Greenfield, M. (2004). First Trimester Miscarriage. Retrieved May 2, 2008, from The Dr. Spock Company Web site: http://www. drspock. com/article/0,1510,4444,00. html Lewis, M. (2001). Second Trimester Complications that May Cause Miscarriage: Incompetent Cervix, Placenta Abruption, and Prenatal Testing. Retrieved on May 3, 2008 from Suite 101 Web site: http://www. suite101. com/article. cfm/pregnancy_after_miscarriage/58284 Mother & Child Glossary. Retrieved May 2, 2008, from Health on the Net Foundation Web site: http://www. hon. ch/Dossier/MotherChild/pregnancy/teratogens.html Murkoff, H. , Eisenberg, A. , & Hathaway, S. (2002). What to Expect When You’re Expecting, 3rd Edition. New York: Workman Publishing. Rosenthal, S. (1998). Problems In the First Trimester. The Fertility Sourcebook.
Retrieved May 2, 2008, from WebMD, Inc. Web site: http://www. webmd. com/content/Article/4/1680_51231. htm The Visible Embryo. Retrieved May 2, 2008, from Creative Commons Web site: http://www. visembryo. com/baby/index. html Watson, S. How Pregnancy Works. Retrieved May 2, 2008, from How Stuff Works, Inc Web site: http://health. howstuffworks. com/pregnancy1. htm
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