Have you ever wondered why some babies are born with birth defects? Intellectual disabilities? Born too early? Through studying prenatal development, we can begin to understand the answers to all these questions.
- What is prenatal development?
- What are the key stages of prenatal development?
- What are factors affecting prenatal development?
Prenatal Development Definition
Prenatal development is the period from the conception of the zygote to the baby's birth. During this phase, the baby develops from a fertilized egg to a fully formed tiny human.
Stages of Prenatal Development
The following text describes in detail three major prenatal developmental phases.
Germinal Phase of Development
The germinal phase includes the fertilization of the egg and continual cell division from a couple of cells to a couple of hundreds. After these first two weeks, the developing zygote enters the embryonic phase.
The germinal period is the first phase of prenatal development that the zygote undergoes, encompassing the first two weeks after conception.
The zygote is the fertilized egg that will eventually develop into the fetus.
Embryonic Phase of Development
The embryonic development period lasts from the second to the eighth week. This phase is crucial in laying the groundwork for developing bodily structures and organs.
Once the zygote enters this phase, it is now called an embryo. The embryo continues the process of cell division and begins to form its structures. Around weeks three to five, the beginning of the embryo’s brain is formed. The external body structures, such as the eyes and ears, begin to take shape by weeks five to eight.
Organogenesis also begins during the embryonic phase, when the internal organs start to form.
At the end of the embryonic period, the embryo is around one inch long.
Fetal Phase of Development
The fetal development period lasts from the ninth week until the baby is born. As soon as the embryo enters this period, it becomes a fetus and remains one until delivered. The fetal phase is the longest and contains the most development.
During the fetal development phase, the organs become differentiated and start to function independently. At the beginning of this phase, the fetus can react to touch and begins to move its fingers. Starting at around 16 weeks, the mother begins to feel the fetus move since it is getting strong enough to make larger movements. Around the same time, the fetus can be stimulated by light and sound and continues to develop its facial features. Between 16 to 20 weeks, doctors can tell the sex of the baby through an ultrasound.
Although the fetus is becoming stronger at the beginning of the fetal phase and is rapidly developing its brain neurons, it is still unable to survive outside of the womb. However, around 22 weeks, it enters the age of viability.
The age of viability is when the fetus, if born prematurely, would be able to survive outside of the womb. Not all babies survive, with 22 to 26 weeks yielding the lowest survival rates.
Even though the fetus still would have had weeks of development left, we thankfully have the technology to support prematurely born babies to regulate their body temperature and help them breathe.
If the fetus is not born prematurely, major organs and muscles continue to grow in the third month of development. The nervous system becomes connected, and the lungs can contract and expand. Even the fetus’ tiny fingernails and toenails are formed. Development continues throughout the pregnancy. The third and final trimester lasts from 27 weeks to the baby's birth. Here, the lungs mature, the baby develops a layer of fat under its skin, and the baby develops its fingerprint.
Prematurely Born Babies
Once the babies are at the age of viability, they can survive if born prematurely - not all do, but they now have a chance. A prematurely born baby, also called a premie, is considered a baby born before 37 weeks of pregnancy (compared to a full-term baby carried for 40 weeks). A baby born between weeks 32 and 36 is a moderate to late premie, weeks 28 to 32 is very premature, and any baby born before 28 weeks is considered extremely premature.
Fig. 1 Mother and her prematurely born baby. wikimedia commons.
What Causes a Baby to Be Born Prematurely?
Many reasons can cause a baby to be born early. To start, the mother's health is an important feature of pregnancy, and if the mother’s health is poor, it could cause the baby to be a premie. If a mother is experiencing abuse, lack of nutrients, or other stressful life events that put extreme pressure on the prenatal environment, it could lead to a prematurely born baby. If the mother’s health is at risk, doctors perform a Cesarean section to deliver the baby before it reaches full term. Concurrently, the mother’s age is a factor in the birth of a child. While getting pregnant at an older age is a risk for the mother and the baby, it can also lead to more premature births.
Furthermore, multiple babies in the mother’s womb will cause the births to be premature. This is simply due to a lack of space. As the babies continue to develop, the mother’s womb gets to a point where it can no longer sufficiently house and provide for the babies.
Factors Affecting Prenatal Development
While 95-98% of babies are born without birth defects, every so often, it happens.
Genetic Factors
One of the reasons for a baby being born with a disability is its genes or the combination of chromosomes. Technology has developed to the point where pregnant mothers can be screened to know if their baby will be born with a genetic condition.
Down Syndrome
Infants born with down syndrome have an extra chromosome, chromosome 21, which attached itself during the conception of the zygote. Mothers who become pregnant before the age of 18 and after 35 are at a higher risk of giving birth to a baby with down syndrome. People with down syndrome typically have slower physical development and intellectual disabilities.
Tay-Sachs Disease
Tay-Sachs is a genetic disorder that the parents pass on to their children. This disease causes the child to have difficulties breaking down fatty matter in the body, leading to buildups in the spine and brain. This matter keeps building up until the child suffers from malfunctioning of their nerves, eventually leading to an early death. The majority of children who suffer from Tay-Sachs disease are from an Eastern European Jewish background and do not live past the age of four. Currently, there is no cure.
Marfan Syndrome
Marfan syndrome is a genetic disorder that manifests itself physically as it does internally. People with this disorder are usually tall and lean, have especially long limbs and fingers, and many either have a concave or convex chest. Internally, people with this syndrome have heart problems, often including high blood pressure and heart murmurs, as well as difficulty seeing.
Cystic Fibrosis
Babies are born with cystic fibrosis due to a mutation in one of their genes, requiring that both parents possess this gene for them to have a baby with cystic fibrosis. This disease causes the body to be unable to regulate mucus and sweat production, leading to a buildup in key areas of the body – the lungs and other internal organs. Parents can be tested to see if they carry the cystic fibrosis gene.
Environmental Factors
Along with the genetic factors are the prenatal environmental factors that can affect the baby's health.
The leading environmental factor, a teratogen, is any harmful substance the mother ingests that can lead to harming the baby.
Any harmful substance that the mother uses goes through her blood, the placenta, the umbilical cord, and to the baby.
Mothers who use drugs while pregnant put their babies at a high risk of being born addicted to the same drug. After the baby is born, it goes through withdrawals, just as an adult would. However, these withdrawals can lead to potential physical and intellectual damage.
A mother who consumes excessive amounts of alcohol during pregnancy could have a baby with fetal alcohol syndrome disorder (FASD). Babies born with FASD will have facial deformities, intellectual disabilities, and physical growth problems.
Fig. 2 An infant with FASD. wikimedia commons.
If the mother has AIDS, she can pass it on to her baby. Smoking can lead to early birth and an underweight baby. If a mother is exposed to radiation, she is at a higher risk of giving birth to a baby with an intellectual disability and physical irregularities.
Of course, if a mother uses drugs once, her baby is not at high risk of being born addicted compared to a mother who is an addict. However, it still has a significantly higher risk than a baby from a mother not using any drugs. Since the mother is creating life, it is essential that she does not ingest any substance that would harm the baby in addition to existing in a less stressful environment.
Prenatal development and the Newborn - Key takeaways
- The germinal phase is the first two weeks after conception when the zygote, the fertilized egg, begins the process of cell division.
- The embryonic phase is the third to eighth week when major organ and bodily structure development occurs. During this phase, the zygote becomes an embryo.
- The fetal phase is the ninth week until the baby is born, when the development of all organs and body parts continues. Around 22 weeks, the baby enters the age of viability, the age at which a prematurely born baby could survive with the help of modern technology.
- The mother's health, the prenatal environment, multiple babies, and the mother's age are factors for a baby to be born prematurely.
- Combinations of genes or extra chromosomes can lead to genetic deformities such as down syndrome, Tay-Sachs disease, Marfan syndrome, or cystic fibrosis.
- If the mother ingests harmful substances (drugs, alcohol, or other teratogens) when pregnant, she puts her baby at a higher risk to be born with disabilities.
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