Prenatal Development - Baby, Stages, Average, Definition, Description, Common Problems (2023)

Definition

Prenatal development refers to the process by which a baby develops from a single cell to an embryo and then to a fetus after conception.

description

The average length of prenatal development is 38 weeks from the date of conception. During this time, a single-celled zygote develops through several stages until it becomes a full-term baby. The three main stages of prenatal development are the germinal stage, the embryonic stage, and the fetal stage.

germination stage

Conception occurs when the female egg (ovum) is fertilized by a male sperm. Under normal circumstances, a woman's ovary releases an egg about once a month during a process called ovulation. The egg enters a fallopian tube, a structure that carries the egg from the ovary to the uterus. For fertilization to occur, sperm ejaculated during intercourse (or introduced during artificial insemination) must have traveled from the vagina to the uterus, in a substance called semen, and then to the fallopian tube, where the egg was released. This process can take up to ten hours after ejaculation. For fertilization to take place, a sperm must penetrate the tough outer membrane of the egg, the so-called zona pellucida. When a sperm successfully attaches to the zona pellucida, a series of chemical reactions take place to allow only that sperm to enter. Fertilization occurs when the sperm successfully penetrates the membrane of the egg. The genetic material from the sperm and egg then combine into a single cell called a zygote and the germinal stage of prenatal development begins.

The zygote soon begins to divide rapidly in a process called fission, first into two identical cells called blastomeres, which then divide into four cells, then eight, and so on. The group of diving cells begins to move along the fallopian tube towards the uterus. About sixty hours after fertilization, about sixteen cells have formed in the so-called morula, which is still surrounded by the zona pellucida; Three days after fertilization, the morula enters the uterus. As cell division proceeds, a fluid-filled cavity called the blastocoel forms in the center of the cell group, containing the outer cell envelope, the trophoblast, and an inner cell mass, the embryoblast. 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 by which the blastocyst attaches to the wall of the uterus, occurs about six days after conception. Hormones secreted by the mother's ovaries and a chemical secreted by the trophoblasts begin to prepare the uterine wall. The blastocyst first attaches to the wall and then migrates to the uterine tissues. Implantation marks the end of the germinal stage and the beginning of the embryonic stage.

Embryonic Stadium

The embryonic stage begins after implantation and lasts up to eight weeks after conception. Soon after implantation, cells continue to divide rapidly, and groups of cells begin to take on different functions (called differentiation). One process (gastrulation) leads to the formation of three distinct layers called the germ layers: the ectoderm (outer layer), the mesoderm (middle layer), and the endoderm (inner layer). As the embryo develops, each germ layer differentiates into different tissues and structures. For example, the ectoderm eventually forms the skin, nails, hair, brain, nerve tissue and cells, the nose, sinuses, mouth, anus, tooth enamel, and other tissues. Mesoderm develops into muscle, bone, cardiac tissue, lungs, reproductive organs, lymphatic tissue, and other tissues. The endoderm forms the lining of the lungs, bladder, digestive tract, tongue, tonsils, and other organs.

The differentiation process takes place over a period of weeks, with different structures forming at the same time. Some of the main events that occur during the embryonic phase are the following:

• Week 3: The development of the brain, heart, blood cells, circulatory system, spinal cord, and digestive system begins.
• Week 4: Beginning of development of bones, facial structures, and limbs (presence of arm and leg buds); Further development of the heart (which begins to beat), the brain, and nerve tissue.
• Week 5: Beginning of development of eyes, nose, kidneys, lungs; Further development of the heart (valve formation), brain, nervous tissue, and digestive tract.
• Week 6: Beginning of development of hands, feet and fingers; Greater development of the brain, heart and circulatory system.
• Week 7: Beginning of the development of hair follicles, nipples, eyelids and sexual organs (testicles or ovaries); first urine formation in the kidneys and first evidence of brain waves.
• Week 8: More pronounced facial features, internal organs well developed, brain can signal muscle movements, heart development completes, external sex organs begin to form.

By the end of the embryonic stage, all essential external and internal structures are formed. The embryo is now called a fetus.

Fotales Stadium

Prenatal development is most dramatic during the fetal stage. When an embryo develops into a fetus at eight weeks, it is about 3 centimeters long from crown to rump and weighs about 3 grams (0.1 ounces). When the fetus is considered full term at 38 weeks gestation, it can weigh 50 centimeters (20 inches) or 3.3 kilograms (7.3 pounds). Although all organ systems are formed during embryonic development, they continue to develop and grow during the fetal period. Examples of some of the key features of fetal development by week are as follows:

• Weeks 9-12: The fetus reaches about 8 cm. (3.2 inches) long; The head is about half the size of the fetus. External features such as the face, neck, eyelids, limbs, fingers, and genitalia are well formed. The beginnings of the teeth appear and the production of red blood cells in the liver begins. The fetus can make a fist.
• Weeks 13-15: The fetus reaches about 15 cm. (6 inches) long. Fine hair called lanugo develops first on the head; Structures such as the lungs, sweat glands, muscles, and bones continue to develop. The fetus can swallow and make sucking movements.
• Weeks 16-20: The fetus reaches about 20 cm. (8 inches) long. Lanugo begins to cover all surfaces of the skin, and fat begins to develop under the skin. Features such as fingernails, toenails, eyebrows, and eyelashes appear. The fetus becomes more active and the mother can sometimes begin to feel fetal movements at this stage.
• Week 21-24: The fetus reaches about 28.5 cm. (11.2 in) long and weighs approximately 0.7 kg (1 lb. 10 oz.). Hair grows longer on the head, and eyebrows and eyelashes are gone. The lungs continue to develop with the formation of air sacs (alveoli); The eyes are coming to an end. At this point, a startle reflex develops.
• 25-28 Week: The fetus will measure about 38 cm. (15 in) long and weighs about 1.2 kg (2 lb 11 ounces). The next few weeks mark a period of rapid brain and nervous system development. The fetus gains more control over movements such as opening and closing the eyelids and certain bodily functions. The lungs have developed to the point where it is possible to breathe air.
• Week 29-32: The fetus reaches about 38-43 cm. (15–17 in.) long and weighs about 2 kg (4 lb 6 oz). Fat deposits become more pronounced under the skin. The lungs remain immature, but respiratory movements begin. The fetal bones are developed but not yet hardened.
• Week 33-36: The fetus reaches about 41-48 cm. (16–19 in.) long and weighs 2.6–3.0 kg (5 lb 12 oz to 6 lb 12 oz). Body fat continues to increase, the lanugo begins to disappear, and the nails have grown. The fetus has gained a high level of control over bodily functions.
• Week 36-38: The fetus reaches a size of 48-53 cm. (19-21 in.) in length is considered an adult at the end of this period. Lanugo has all but disappeared, being replaced by thicker hair on top of the head. The nails have grown beyond the tips of the fingers. In a healthy fetus, all organ systems function.

general problems

Although 90 percent of babies born in the United States are considered healthy, abnormalities that are considered congenital (inherited or due to a genetic abnormality) or environmental (such as abnormalities caused by materials) can occur during prenatal development. In other cases, problems can arise when a fetus is born prematurely.

congenital anomalies

In some cases, abnormalities can occur during prenatal development that result in physical deformities or developmental delays, or affect different parts of the body after the baby is born. The cause can be a small mutation or damage to the genetic material of the cells, or a large chromosomal abnormality (each normal cell has two copies of every 23 strands [called chromosomes] of genetic material, and abnormalities can occur when there are three copies of one strand or just one). Sometimes the abnormality is inherited from one or both parents; in other cases, the defect is caused by an error in prenatal development.

Some abnormalities are minor and do not affect the long-term prognosis after delivery. At the other end of the spectrum, abnormalities can be so severe that stillbirth is inevitable. About 10 to 15 percent of pregnancies end before the 20th week, a process called miscarriage, or miscarriage; Congenital anomalies account for a significant proportion of spontaneous abortions. Genetic abnormalities account for about 5 percent of miscarriages.

maternal abnormalities

The mother's age, health status, nutritional status, and environment are closely related to the health of a growing embryo or fetus. Some examples of environmental factors that can lead to developmental delays include:

• Age: As of 2004, research has shown that babies born to mothers between the ages of seventeen and thirty-five tend to be healthier. One reason is that the risk of certain birth defects such asDown syndromeincreases with maternal age (particularly in mothers older than 40 years). Another reason is that the risk of complications in pregnancy or childbirth is higher in women older than 35 years.
• Medical Conditions: In some cases, a mother can transmit a viral or bacterial infection to the fetus, such as: B in humans immunodeficiency virus (HIV). In other cases, the mother's disease can cause birth defects; an example is rubella , which can cause heart defects, deafness, developmental delays, and other problems in the fetus if the mother contracts it during pregnancy.
• Nutritional status: A balanced diet rich in nutrients such as folic acid , Calcium, Iron, Zinc, Vitamin D and B vitamins It is recommended for pregnant women. Certain vitamin and mineral deficiencies can interfere with normal prenatal development. For example, a lack of folic acid in early pregnancy can lead to neural tube defects such as spina bifida . It is recommended that mothers consume about 300 additional calories per day (in addition to a normal non-pregnancy diet) to support fetal growth and development.
• Other Environmental Factors: Exposure to certain substances called teratogens (agents that can affect prenatal development) during pregnancy can cause embryonic or fetal birth defects. Examples of teratogens include alcohol, thalidomide, cocaine, certain anti-seizure medications, diethylstilbestrol (DES), and the acne medication Accutane.

precocity

Advances in medical care have allowed many premature babies to survive and develop normally. The earlier the gestational age, the greater the chance of death or serious medical problems. Whether or not a premature baby survives is closely related to its gestational age:

• 21 weeks or less: 0% survival rate
• 22 weeks: 0-10 percent survival rate
• 23 weeks: 10-35 percent survival rate
• 24 weeks: 40-70 percent survival rate
• 25 weeks: 50-80 percent survival rate
• 26 weeks: 80-90 percent survival rate
• 27 weeks: Survival rate of more than 90 percent

parental concerns

Many parents have questions or concerns about the prenatal development of an existing or expecting child and what steps they need to take to ensure their child's health. During prenatal visits to an obstetrician, a pregnant mother should be properly informed nutrition and prenatal care; Prenatal vitamins are often prescribed to prevent nutritional deficiencies. Prenatal tests are often recommended for parents-to-be to assess the health of the fetus and the risk of developing certain medical conditions. Some common prenatal tests related to prenatal development are as follows:

• Blood tests to detect diseases that could affect the fetus, such as B. HIV,Hepatitis B, or other sexually transmitted diseases
• blood tests to see if the mother has a protein called Rh factor in her red blood cells; If she doesn't and her baby does (depending on whether the father is Rh positive or not), she needs treatment to prevent a potentially harmful reaction to the baby.
• Chorionic villus sampling, a prenatal test that uses a needle to take a small sample of the placenta to check for chromosomal abnormalities.
• nuchal fold screening or nuchal translucency, which measures a small space in the fetal neck with ultrasound; Fetuses with larger nuchal folds are at higher risk of having a chromosomal abnormality
• Amniocentesis, a test in which a sample of the fluid that surrounds the fetus in the womb is taken to identify certain genetic disorders, birth defects, or the maturity of the fetal lungs.

BOOKS

Gilbert, Scott F.Developmental biology, 6th edition Sunderland, MA: Sinauer Associates, Inc., 2000.

MAGAZINES

Miller, Sharon M., and Jeanne M. Isabel. "Prenatal screening tests facilitate risk assessment."medical laboratory observer34, no. 2 (February 2002): 8–21.

THE ORGANIZATION

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

Information Resource Center (IRC) of the National Institute for Child Health and Human Development (NICHD).PO Box 3006, Rockville, MD 20847. Sitio web: http://www.nichd.nih.gov.

WEBSITES

Hill, Mark.UNSW Embryology, 2004. Available online athttp://embryology.med.unsw.edu.au(Accessed December 11, 2004).

McPherson, Katrina. "Development of the fetus".Medline Plus, May 8, 2004. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002398.htm (accessed December 11, 2004).