Students are taught how babies are formed, i.e., during conception. However, do you know what happens from conception until an infant is born? Do you wonder what leads to some pregnancies being at high risk? These are the questions covered in the field of prenatal development.
The moment of conception, when two single cells—one from a male and the other from a female—join to form a new cell known as a zygote, is the initial stage in the formation of a human being. This event releases potent genetic forces that will impact the person for the rest of their life. However, up until quite recently, little was understood about prenatal development. As a result, it was difficult to understand how the experiences of the pregnant mother and the intrauterine development and experiences of the child were related. With technological advancements, there is a better understanding of the processes involved in a zygote developing into a baby. These processes are studied during prenatal development. Prenatal development starts with fertilization in the germinal stage of embryonic development and continues in fetal development until birth.
The gestational period for a human infant is 38 weeks or roughly 265 days. Three unequally long phases, each lasting 38 weeks, are separated by distinct changes in the developing organism. The three stages are−
Germinal stage
Embryonic stage
Fetal stage
This stage starts at conception and concludes with the zygote's implantation in the uterine wall. After conception, the embryo swims for about a week through the fallopian tube to the uterus. Within 24 to 36 hours of conception, cell division starts; within 2 to 3 days, there are several dozen cells, and the entire mass is about the size of a pin. The mass of cells, known as a blastocyst, starts to divide around four days after conception and eventually forms a sphere with two layers of cells surrounding a hollow center.
The many structures that sustain the growing creature are formed in the outermost layer, whereas the embryo is formed in the inner layer. The many structures that sustain the growing creature are formed in the outermost layer, whereas the embryo is formed in the inner layer. The blastocyst's outer cell layer disintegrates as it comes into contact with the uterine wall. Implantation, the process of attaching the cell mass to the uterine wall, involves the development of tiny tendrils. The blastocyst has approximately 150 cells when implantation is complete (often ten days to 2 weeks after conception).
The end of implantation marks the start of the embryonic stage. The outer layer of cells in the blastocyst specializes in two membranes, each of which creates essential support structures. The inner membrane develops into the amnion, a sac or bag that contains the embryo and amniotic fluid. The placenta and the umbilical cord are formed from the outer membrane, known as the chorion. A plate-like mass of cells called the placenta rests against the uterine wall when the pregnancy is around four weeks. It acts as the embryo's liver and kidneys until its organs start functioning. It also provides the embryo with oxygen and eliminates carbon dioxide from its circulation.
The most significant advancement at this point is a process known as organogenesis. Organogenesis is the process by which the mass of cells that will eventually make up the embryo differentiates further into several cell types that ultimately become the basic components of the skin, sensory receptors, nerve cells, muscles, circulatory system, and internal organs. A heartbeat can be heard around four weeks after conception, and the first signals of the lungs and limbs are also discernible. The basic parts of the nervous system and the rudimentary fingers and toes, eyes, eyelids, nose, mouth, and external ears, are all present by the end of the embryonic phase.
Once organogenesis is complete, the developing organism enters the fetal stage, the last phase of prenatal development, at which point it is referred to as a fetus. The fetal period lasts from around eight weeks before delivery, is very important for brain development, and includes numerous characteristics like listening to the mother's voice, establishing reflex actions, etc. The fetus grows from weighing approximately 14 ounces and measuring 1 inch in length to a baby weighing approximately 7 pounds and roughly 20 inches long when prepared for delivery. The organ systems required for life outside the womb are also developed during this phase.
According to some researchers, establishing norms for prenatal behavior would enable healthcare professionals to evaluate fetal health and anticipate postnatal issues accurately. Hence, this has been the focus of several recent studies. These investigations have yielded some awe-inspiring results. Scientists have discovered that the fetus responds to sounds by changing its heart rate, turning its head, and moving its body as early as the 25th week of pregnancy. The same methods used to study brain function postnatally, such as magnetic resonance imaging, have been employed to scan the mother's abdomen to monitor fetal brain activity (MRI). These methods have been used in studies to discover that late-term fetuses respond to sounds in both neurological and behavioral ways.
Research also suggests that the fetus can distinguish between familiar and novel stimuli by the 32nd or 33rd week. There has been evidence of prenatal learning of rhymes and stories in quite a few studies. The fetus reacts to familiar sounds during prenatal and after birth, and Developmentalists are investigating whether and how prenatal learning influences later development.
Prenatal development is not free of errors. The possible issues can be divided into two broad categories: chromosomal and genetic issues that start at conception and issues brought on by teratogens, which are harmful agents or circumstances.
Heredity is not free of errors. There can be errors in processes that involve the division of chromosomes, and genes can either undergo mutations, or recessive genes can be expressed if inherited from both parents, leading to disorders of various sorts. Researchers study these abnormalities at the cellular level to understand diagnostic measures and help parents make informed decisions regarding their pregnancy.
Maternal conditions like rubella, HIV/AIDS, and chronic illnesses like heart disease, diabetes, and lupus have been shown to exhibit a negative effect on prenatal development. Additionally, environmental teratogens, i.e., substances present in the environment, can hamper prenatal development; for example, high mercury, lead, or arsenic exposure are all harmful to prenatal development. Consumption of alcohol, tobacco, and drugs can also affect prenatal development negatively. Other factors include the age of the mother, her stress level and emotional state, and her socio-economic status.
Prenatal development is studied better to understand the process of zygote development into a baby. A better understanding of this process and the various factors that influence it has helped reduce prenatal deaths significantly. It can also give us a better understanding of how prenatal development affects an individual's subsequent growth.
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