Table of ContentsView AllTable of ContentsGerminal StageEmbryonic StageFetal StageFrequently Asked Questions
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Germinal Stage
Embryonic Stage
Fetal Stage
Frequently Asked Questions
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While you might think ofchild developmentas something that begins during infancy, the prenatal period is also considered an important part of the developmental process. The prenatal development stages are a time of remarkable change that helps set the stage for futurepsychologicaldevelopment. The brain develops over the course of the prenatal period, but it will continue to go through more changes during the early years of childhood
There are three stages of prenatal development: the germinal, embryonic, and fetal stages.
The first two weeks after conception are known as the germinal stage, the third through the eighth week is known as the embryonic period, and the time from the ninth week until birth is known as the fetal period.
At a GlanceThe three prenatal development stages involve the processes that occur from conception to birth. The first stage, known as the germinal stage, involves the formation of the zygote and early cell division. The second stage, called the embryonic stage, involves the early growth of the embryo, including the formation of the neural tube, which will eventually become the brain and spinal cord. The fetal period is the longest stage of prenatal development, and is when the organs, tissues, and body grow. Keep reading to learn more about the events that take place during each of these stages of prenatal development.
At a Glance
The three prenatal development stages involve the processes that occur from conception to birth. The first stage, known as the germinal stage, involves the formation of the zygote and early cell division. The second stage, called the embryonic stage, involves the early growth of the embryo, including the formation of the neural tube, which will eventually become the brain and spinal cord. The fetal period is the longest stage of prenatal development, and is when the organs, tissues, and body grow. Keep reading to learn more about the events that take place during each of these stages of prenatal development.
2:05Click Play to Learn More About the Stages of Prenatal Development
2:05
Click Play to Learn More About the Stages of Prenatal Development
Germinal Stage of Prenatal Development
The germinal stage begins at conception when the sperm and egg cell unite in one of the two fallopian tubes. The fertilized egg is called a zygote. Just a few hours after conception, the single-celled zygote begins making a journey down the fallopian tube to the uterus.
Important Events:Formation of the zygoteRapid cell divisionFormation of the blastocystJourney from the fallopian tube to the uterusImplantation
Important Events:
Formation of the zygoteRapid cell divisionFormation of the blastocystJourney from the fallopian tube to the uterusImplantation
Cell Division
Cell division begins approximately 24 to 36 hours after conception. Through the process of mitosis, the zygote first divides into two cells, then into four, eight, sixteen, and so on.
A significant number of zygotes never progress past this early part of cell division, with as many as half of all zygotes surviving less than two weeks.
Cell Differentiation
Once the eight-cell point has been reached, the cells begin to differentiate and take on certain characteristics that will determine the type of cells they will eventually become. As the cells multiply, they will also separate into two distinctive masses: the outer cells will eventually become the placenta, while the inner cells form the embryo.
Blastocyst Development
Cell division continues at a rapid rate during the approximately week-long journey from fallopian tube to uterus wall. The cells develop into what is known as a blastocyst. The blastocyst is made up of three layers, each of which develops into different structures in the body.
Implantation
Finally, the blastocyst arrives at the uterus and attaches to the uterine wall, a process known as implantation. Implantation occurs when the cells nestle into the uterine lining and rupture tiny blood vessels. The connective web of blood vessels and membranes that form between them will provide nourishment for the developing being for the next nine months.
However, it is important to recognize that implantation is not always an automatic and sure-fire process.
Researchers estimate that approximately 60% of all natural conceptions never become properly implanted in the uterus, which results in the new life ending before the mother is ever aware she is pregnant.
When implantation is successful, hormonal changes halt the normal menstrual cycle and cause a whole host of physical changes.
Embryonic Stage of Prenatal Development
At this point, the mass of cells is now known as an embryo. The beginning of the third week after conception marks the start of the embryonic period, a time when the mass of cells becomes distinct as a human embryo.
Important Events:Neural tube developmentDevelopment of basic body structuresNeurons form
Neural tube developmentDevelopment of basic body structuresNeurons form
Formation of the Neural Tube
The embryonic stage plays an important role in the development of the brain. Approximately four weeks after conception, the neural tube forms. This tube will later develop into the central nervous system, including the spinal cord and brain.
The neural tube begins to form along with an area known as the neural plate. The earliest signs of neural tube development are the emergence of two ridges that form along each side of the neural plate.
Over the next few days, more ridges form and fold inward until a hollow tube is formed. Once this tube is fully formed, cells begin to form near the center.The tube begins to close, and brain vesicles form. These vesicles will eventually develop intoparts of the brain, including the structures of the forebrain, midbrain, and hindbrain.
Other Basic Structures Start to Form
By the eighth week of development, the embryo has all of the basic organs and parts except those of the sex organs. At this point, the embryo weighs just one gram and is about one inch long.
By the end of the embryonic period, the basic structures of the brain and central nervous system have been established. At this point, the basic structure of theperipheral nervous systemis also defined.
The production ofneurons, or brain cells, begins around day 42 after conception and is mostly complete sometime around the middle of pregnancy.
As neurons form, they migrate to different areas of the brain. Once they have reached the correct location, they begin to form connections with other neural cells, establishing rudimentary neural networks.
Fetal Stage of Prenatal Development
Important Events:Nervous systems forms and basic reflexes emergeSex differentiation occursIncrease in size and development of organs and tissues
Nervous systems forms and basic reflexes emergeSex differentiation occursIncrease in size and development of organs and tissues
Nervous System Develoment
The early body systems and structures established in the embryonic stage continue to develop. The neural tube develops into the brain and spinal cord, and neurons continue to form. Once these neurons have formed, they begin to migrate to their correct locations. Synapses, or the connections between neurons, also begin to develop.
Between the ninth and twelfth week of gestation (at the earliest), reflexes begin to emerge. The fetus begins to make reflexive motions with its arms and legs.
Differentiation of Sex Organs
During the third month of gestation, the sex organs begin to differentiate. By the end of the month, all parts of the body will be formed. At this point, the fetus weighs around three ounces. The fetus continues to grow in both weight and length, although the majority of the physical growth occurs in the later stages of pregnancy.
The end of the third month also marks the end of the first trimester of pregnancy.
Second and Third Trimester Growth
During the second trimester, or months four through six, the heartbeat grows stronger, and other body systems become further developed. Fingernails, hair, eyelashes, and toenails form.Perhaps most noticeably, the fetus increases about six times in size.
So, what’s going on inside the brain during this important period of prenatal development? The brain andcentral nervous systemalso become more responsive during the second trimester. Around 28 weeks, the brain starts to mature faster, with an activity that greatly resembles that of a sleeping newborn.
During the period from seven months until birth, the fetus continues to develop, put on weight, and prepare for life outside the womb. The lungs begin to expand and contract, preparing the muscles for breathing.
While development usually follows this normal pattern, there are times whenproblems with prenatal developmentoccur. Disease, malnutrition, and other prenatal influences can have a powerful impact on how the brain develops during this critical period.
Takeaways
Brain development does not end at birth. A considerable amount of brain development takes place postnatally, including growing insize and volumewhile changing in structure. The brain quadruples in size between birth and preschool. As children learn and have new experiences, some networks in the brain are strengthened while other connections are pruned.
Frequently Asked QuestionsThe first 13 weeks of pregnancy are considered the most critical in prenatal development. It is during this period that the embryo forms organs. It is also the period when most miscarriages occur.The main stages of the embryonic period encompass gastrulation (the ectoderm, mesoderm, and endoderm form), neurulation (formation of neural tissue), organogenesis (development of the organs).Important fetal milestones at each of the prenatal development stages include:Germinal stage: The division of cells and implantation of the blastocyst.Embryonic stage: The development of the neural tube and organs.Fetal stage: Continued growth of organs and physical development in preparation for birth.
The first 13 weeks of pregnancy are considered the most critical in prenatal development. It is during this period that the embryo forms organs. It is also the period when most miscarriages occur.
The main stages of the embryonic period encompass gastrulation (the ectoderm, mesoderm, and endoderm form), neurulation (formation of neural tissue), organogenesis (development of the organs).
Important fetal milestones at each of the prenatal development stages include:Germinal stage: The division of cells and implantation of the blastocyst.Embryonic stage: The development of the neural tube and organs.Fetal stage: Continued growth of organs and physical development in preparation for birth.
Important fetal milestones at each of the prenatal development stages include:
5 SourcesVerywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.National Institutes of Health.What are stem cells, and why are they important?.Ochoa-Bernal MA, Fazleabas AT.Physiologic events of embryo implantation and decidualization in human and non-human primates.Int J Mol Sci. 2020;21(6):1973. doi:10.3390/ijms21061973Rice University.13.1 The Embryologic Perspective. In:Anatomy and Physiology.Rice University.28.3 Fetal Development. InAnatomy and Physiology.U.S. Department of Health and Human Services Office on Women’s Health.Stages of pregnancy.
5 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.National Institutes of Health.What are stem cells, and why are they important?.Ochoa-Bernal MA, Fazleabas AT.Physiologic events of embryo implantation and decidualization in human and non-human primates.Int J Mol Sci. 2020;21(6):1973. doi:10.3390/ijms21061973Rice University.13.1 The Embryologic Perspective. In:Anatomy and Physiology.Rice University.28.3 Fetal Development. InAnatomy and Physiology.U.S. Department of Health and Human Services Office on Women’s Health.Stages of pregnancy.
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
National Institutes of Health.What are stem cells, and why are they important?.Ochoa-Bernal MA, Fazleabas AT.Physiologic events of embryo implantation and decidualization in human and non-human primates.Int J Mol Sci. 2020;21(6):1973. doi:10.3390/ijms21061973Rice University.13.1 The Embryologic Perspective. In:Anatomy and Physiology.Rice University.28.3 Fetal Development. InAnatomy and Physiology.U.S. Department of Health and Human Services Office on Women’s Health.Stages of pregnancy.
National Institutes of Health.What are stem cells, and why are they important?.
Ochoa-Bernal MA, Fazleabas AT.Physiologic events of embryo implantation and decidualization in human and non-human primates.Int J Mol Sci. 2020;21(6):1973. doi:10.3390/ijms21061973
Rice University.13.1 The Embryologic Perspective. In:Anatomy and Physiology.
Rice University.28.3 Fetal Development. InAnatomy and Physiology.
U.S. Department of Health and Human Services Office on Women’s Health.Stages of pregnancy.
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