Reasons for a Small Baby at 38 Weeks

Prenatal development

Prenatal Development 2169

Photograph past: soupstock

Definition

Prenatal development refers to the process in which a baby develops from a single cell after formulation into an embryo and later a fetus.

Description

The average length of time for prenatal evolution to consummate is 38 weeks from the date of conception. During this time, a single-celled zygote develops in a series of stages into a full-term babe. The three primary stages of prenatal development are the germinal phase, the embryonic phase, and the fetal stage.

Germinal stage

Formulation occurs when the female egg (ovum) is fertilized by a the male person sperm. Under normal circumstances, i egg is released approximately once a month from a woman'southward ovary during a process called ovulation. The egg makes its way into a fallopian tube, a structure that guides the egg abroad from the ovary toward the uterus. For fertilization to occur, sperm ejaculated during sexual intercourse (or introduced during artificial insemination) in a substance called semen must accept made their way from the vagina into the uterus and afterward into the fallopian tube where the ovum has been released. This process can have up to ten hours afterwards ejaculation. For fertilization to occur, a sperm must penetrate the tough outer membrane of the egg called the zona pellucida. When one sperm successfully binds with the zona pellucida, a series of chemical reactions occurs to allow simply that sperm to penetrate. Fertilization occurs when the sperm successfully enters the ovum'southward membrane. The genetic material of the sperm and egg and so combine to form a single cell called a zygote and the germinal stage of prenatal development commences.

The zygote soon begins to separate rapidly in a procedure called cleavage, first into two identical cells called blastomeres, which further dissever to iv cells, then into eight, and then on. The grouping of diving cells begins to move forth the fallopian tube toward the uterus. Well-nigh lx hours subsequently fertilization, approximately sixteen cells accept formed to what is called a morula, still enclosed by the zona pellucida; three days later on fertilization, the morula enters the uterus. Every bit prison cell partitioning continues, a fluid-filled cavity called a blastocoele forms in the eye of the group of cells, with the outer shell of cells called trophoblasts and an inner mass of cells chosen embryoblasts. The zona pellucida disappears and the morula becomes a blastocyst. At this stage the blastocyst consists of 200 to 300 cells and is ready for implantation.

Implantation, the process in which the blastocyst implants into the uterine wall, occurs approximately six days after formulation. Hormones secreted from the female parent'south ovaries and a chemical secreted past the trophoblasts brainstorm to set the uterine wall. The blastocyst first adheres to the wall and so moves into the uterine tissue. Implantation marks the end of the germinal phase and the starting time of the embryonic stage.

Embryonic phase

The embryonic stage begins after implantation and lasts until viii weeks afterwards conception. Soon after implantation, the cells keep to rapidly split and clusters of cells begin to take on different functions (called differentiation). A process (gastrulation) leads to the formation of three distinct layers called germ layers: the ectoderm (outer layer), the mesoderm (middle layer), and the endoderm (inner layer). Equally the embryo develops, each germ layer differentiates into dissimilar tissues and structures. For example, the ectoderm somewhen forms skin, nails, pilus, brain, nervous tissue and cells, nose, sinuses, mouth, anus, tooth enamel, and other tissues. The mesoderm develops into muscles, basic, middle tissue, lungs, reproductive organs, lymphatic tissue, and other tissues. The endoderm forms the lining of lungs, bladder, digestive tract, tongue, tonsils, and other organs.

The process of differentiation takes identify over a period of weeks with different structures forming simultaneously. Some of the major events that occur during the embryonic stage are as follows:

Illustration of prenatal development, from the two-cell, or zygote, stage through the embryonic stage, in which the major body systems develop, to the fetal stage, during which the babys brain develops and the body adds size and weight. (Illust

Illustration of prenatal development, from the 2-cell, or zygote, stage through the embryonic stage, in which the major body systems develop, to the fetal stage, during which the baby's brain develops and the torso adds size and weight.

(Illustration past GGS Information Services.)

Calendar week 3: Beginning evolution of the brain, centre, blood cells, circulatory arrangement, spinal string, and digestive arrangement.
Week 4: First evolution of bones, facial structures, and limbs (presence of arm and leg buds); continuing evolution of the heart (which begins to beat), brain, and nervous tissue.
Calendar week 5: Beginning development of eyes, nose, kidneys, lungs; continuing development of the middle (germination of valves), brain, nervous tissue, and digestive tract.
Week 6: Kickoff development of hands, anxiety, and digits; continuing development of brain, heart, and circulation system.
Calendar week seven: Beginning development of hair follicles, nipples, eyelids, and sex organs (testes or ovaries); first formation of urine in the kidneys and starting time evidence of brain waves.
Week 8: Facial features more distinct, internal organs well developed, the brain can indicate for muscles to move, heart evolution ends, external sex organs begin to form.

Past the finish of the embryonic phase, all essential external and internal structures take been formed. The embryo is now referred to as a fetus.

Fetal phase

Prenatal development is most dramatic during the fetal stage. When an embryo becomes a fetus at eight weeks, it is approximately three centimeters (1.ii inches) in length from crown to rump and weighs near 3 grams (0.1 ounce). By the time the fetus is considered total-term at 38 weeks gestation, he or she may be fifty centimeters (20 inches) or 3.3 kilograms (7.3 pounds). Although all of the organ systems were formed during embryonic development, they go on to develop and grow during the fetal stage. Examples of some of the major features of fetal evolution by week are as follows:

Weeks 9–12: The fetus reaches approximately 8 cm. (3.two in.) in length; the head is approximately half the size of the fetus. External features such as the face, neck, eyelids, limbs, digits, and genitals are well formed. The beginnings of teeth appear, and red blood cells begin to be produced in the liver. The fetus is able to make a fist.
Weeks 13–15: The fetus reaches approximately 15 cm. (half-dozen in.) in length. Fine hair called lanugo first develops on the caput; structures such as the lungs, sweat glands, muscles, and bones go along to develop. The fetus is able to eat and make sucking motions.
Weeks sixteen–20: The fetus reaches approximately 20 cm. (8 in.) in length. Lanugo begins to encompass all skin surfaces, and fat begins to develop under the skin. Features such equally finger and toenails, eyebrows, and eyelashes appear. The fetus becomes more active, and the mother tin can sometimes brainstorm to feel fetal movements at this stage.
Weeks 21–24: The fetus reaches approximately 28.5 cm. (11.two in.) in length and weighs approximately 0.7 kg (1 lb. 10 oz.). Hair grows longer on the caput, and the eyebrows and heart lashes finish forming. The lungs continue to develop with the formation of air sac (alveoli); the optics finish developing. A startle reflex develops at this time.
Weeks 25–28: The fetus reaches approximately 38 cm. (15 in.) in length and weighs approximately i.2 kg (2 lb. xi oz.). The side by side few weeks marking a menses of rapid brain and nervous system evolution. The fetus gains greater control over movements such equally opening and endmost eyelids and certain torso functions. The lungs take developed sufficiently that air breathing is possible.
Weeks 29–32: The fetus reaches approximately 38–43 cm. (15–17 in.) in length and weighs approximately 2 kg (iv lb. 6 oz.). Fat deposits become more than pronounced under the skin. The lungs remain young but breathing movements begin. The fetus'southward bones are developed just non nonetheless hardened.
Weeks 33–36: The fetus reaches approximately 41–48 cm. (xvi–xix in.) in length and weighs ii.6–3.0 kg (5 lb. 12 oz. to 6 lb. 12 oz.). Trunk fat continues to increase, lanugo begins to disappear, and fingernails are fully grown. The fetus has gained a loftier caste of control over torso functions.
Weeks 36–38: The fetus reaches 48–53 cm. (nineteen–21 in.) in length is considered to exist full-term by the end of this flow. Lanugo has generally disappeared and is replaced with thicker hair on the head. Fingernails accept grown past the tips of the fingers. In a healthy fetus, all organ systems are functioning.

Common bug

Although 90 per centum of babies born in the United States are considered healthy, abnormalities may ascend during prenatal evolution that are considered built (inherited or due to a genetic aberration) or environmental (such equally cloth derived abnormalities). In other cases, problems may arise when a fetus is built-in prematurely.

Congenital abnormalities

In some cases abnormalities may arise during prenatal development that cause physical malformations or developmental delays or affect diverse parts of the body subsequently the child is built-in. The cause may be a small mutation in or damage to the genetic material of cells, or a major chromosomal aberration (each normal cell has two copies each of 23 strands [chosen chromosomes] of genetic material, and abnormalities can arise if there are 3 copies of a strand or only one). Sometimes the aberration is inherited from one or both parents; in other cases, the defect occurs because of an fault in prenatal development.

Some abnormalities are minor and do non affect the long-term prognosis once the child is built-in. At the other end of the spectrum, abnormalities may be and so severe that fetal demise is inevitable. Approximately ten to 15 percent of pregnancies terminate before the twentieth week, a procedure called miscarriage or spontaneous ballgame; congenital abnormalities account for a significant proportion of miscarriages. Genetic abnormalities business relationship for approximately 5 percent of miscarriages.

Maternal derived abnormalities

The age, health condition, nutritional condition, and environment of the mother are all closely tied to the health of a growing embryo or fetus. Some examples of environmental factors that may pb to developmental abnormalities include:

Age: As of 2004, research showed that babies born to mothers betwixt the ages of seventeen and thirty-five tend to be healthier. One reason is that the risk of sure built abnormalities such as Down syndrome increases with female parent'due south age (particularly mothers over forty). Another reason is that the risk of having pregnancy or birth complications is greater with women over the age of thirty-5.
Health condition: In some cases a mother may pass a viral or bacterial infection to the fetus, such as in human immunodeficiency virus (HIV). In other cases, a mother'southward illness may cause built malformations; an example is rubella , which tin cause centre defects, deafness, developmental delays, and other issues in a fetus if the mother contracts it during pregnancy.
Nutritional status: A well-balanced diet rich in nutrients such every bit folic acid , calcium, atomic number 26, zinc, vitamin D, and the B vitamins is recommended for pregnant women. Sure vitamin and mineral deficiencies can interfere with normal prenatal development. For case, a deficiency in folic acid during the early on stages of pregnancy may lead to neural tube defects such as spina bifida . Mothers are recommended to eat approximately 300 boosted calories a day (above and beyond a normal non-pregnancy nutrition) to support the fetus's growth and evolution.
Other environmental factors: Exposure to certain substances called teratogens (agents that may interfere with prenatal development) during pregnancy may cause embryonic or fetal malformations. Examples of teratogens include alcohol, thalidomide, cocaine, certain seizure medications, diethylstilbestrol (DES), and the anti-acne drug Accutane.

Prematurity

Advances in medical care have fabricated it possible for many infants built-in prematurely to survive and develop normally. The earlier the gestational age, the greater the chance of death or meaning medical bug. Whether or not a premature infant volition survive is intimately tied to his or her gestational historic period:

21 weeks or less: 0 percent survival charge per unit
22 weeks: 0–10 percent survival rate
23 weeks: 10–35 percent survival rate
24 weeks: 40–lxx percent survival rate
25 weeks: 50–eighty percentage survival rate
26 weeks: 80–ninety percent survival charge per unit
27 weeks: greater than 90 percent survival rate

KEY TERMS

Miscarriage —Loss of the embryo or fetus and other products of pregnancy before the twentieth calendar week. Often, early on in a pregnancy, if the condition of the baby and/or the mother'south uterus are not compatible with sustaining life, the pregnancy stops, and the contents of the uterus are expelled. For this reason, miscarriage is likewise referred to equally spontaneous ballgame.

Ovary —One of the two almond-shaped glands in the female reproductive system responsible for producing eggs and the sexual practice hormones estrogen and progesterone.

Teratogen —Any drug, chemical, maternal affliction, or exposure that tin can cause physical or functional defects in an exposed embryo or fetus.

Uterus —The female person reproductive organ that contains and nourishes a fetus from implantation until birth. Also chosen the womb.

Parental concerns

Many parents have questions or concerns about the prenatal development of an existing or anticipated kid and what steps they should take to ensure their child's health. During prenatal visits to an obstetrician, a pregnant mother should be educated in proper nutrition and prenatal intendance; often, prenatal vitamins are prescribed to avert nutritional deficiencies. Prenatal testing is often recommended to parents-to-be as a means of assessing the fetus'south wellness and the risk of developing certain weather. Some mutual prenatal tests that relate to prenatal evolution are as follows:

blood tests to check for diseases that could affect the fetus, such as HIV, hepatitis B , or other sexually transmitted diseases
blood tests to check if the female parent carries a protein called Rh factor on her red claret cells; if she does not and her baby does (determined by whether the begetter is Rh-positive or not), she will require handling to preclude a potentially damaging reaction to the baby
chorionic villus sampling, a prenatal test that takes a tiny sample of the placenta with a needle to test for chromosomal abnormalities
nuchal fold or nuchal translucency screening test, which measures a minor space at the back of the fetus'southward neck using ultrasound; fetuses with larger nuchal folds take a greater risk of having a chromosomal abnormality
amniocentesis, a test that takes a sample of the fluid that surrounds the fetus in the uterus to identify sure genetic disorders, congenital malformations, or the maturity of the fetus's lungs

Resources

BOOKS

Gilbert, Scott F. Developmental Biology , 6th ed. Sunderland, MA: Sinauer Associates, Inc., 2000.

PERIODICALS

Miller, Sharon M., and Jeanne 1000. Isabel. "Prenatal Screening Tests Facilitate Chance Assessment." Medical Laboratory Observer 34, no. 2 (February 2002): viii–21.

ORGANIZATIONS

March of Dimes Birth Defects Foundation. 1275 Mamaroneck Ave., White Plains, NY 10605. Web site: http://www.marchofdimes.com.

National Institute of Child Health and Human Development (NICHD) Information Resource Center (IRC). PO Box 3006, Rockville, MD 20847. Web site: http://world wide web.nichd.nih.gov.

WEB SITES

Colina, Mark. UNSW Embryology , 2004. Bachelor online at http://embryology.med.unsw.edu.au (accessed Dec 11, 2004).

McPherson, Katrina. "Fetal Development." MedlinePlus , May viii, 2004. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002398.htm (accessed December 11, 2004).

Stephanie Dionne Sherk