The process of conceiving a child and its development inside the body of the mother is a very beautiful and amazing phenomenon. Before it takes its first breath, a human baby has to pass through an incredible and miraculous transformation from a single cell to a complex, self-sustaining organism.
This article contains the stages of development of baby from a single celled Zygote to multicellular human being. Let us proceed step by step.
First Month
Fertilization
The union of male gamete (Sperm) and female gamete (Ovum or egg) is known as Fertilization that produces the first little most body part of a man called a Zygote. The act of fertilization takes place in the female genital tract of a female body. A sperm remain alive for 72 hours after the entering into the vagina, but its capacity to fertilize the ovum lasts for 48 hours. So, the 12th to 18th days of menstruation cycle is correct for getting pregnancy for a lady, because the Ovulation (releasing of ovum or secondary oocyte from the Grafian follicle of the ovary) happens about the 14th day of the menstrual cycle from any one side of the ovary. Although so many sperms encircle the ovum but only one sperm is allowed to penetrate the ovum.
Spermatozoan Fusing with the egg
After fertilization in the female’s fallopian tube, the nuclei of the sperm and egg fuse to form a new cell (the zygote).This cell contains 46 chromosomes, 23 from each parent cell. As the zygote travels to the uterus, it divides, forming a cluster of cells (the morula) by about 3 days after fertilization. The morula develops a cavity and is now known as a blastocyst, which will become the embryo. This blastocyst floats freely within the uterine cavity for about 48 hours before attaching itself to a site in the endometrium (uterine lining). About 10 days following fertilization, the blastocyst is completely imbedded into the endometrium, and forms the placenta. Within the cell cover of the blastocyst’s cavity, it then develops into a fluid- filled sac covering the embryo, and the yolk sac.
What Determinines the sex of the baby?
In Human beings, the normal chromosome count is 46, 44 of which are autosomes and two are sex chromosomes which determine the sex of a baby. The sex chromosomes make an organism male or female. In humans and many other organisms, the sex chromosomes are X and Y, where XX is female (the homogametic sex) and XY is male (the heterogametic sex).Whether the individual will be male (XY) or female (XX), depends on the chromosome the sperm carries. If the sperm that fertilizes the egg carries the X chromosome, the offspring will be female (XX) and if the sperm carries the Y chromosome, the offspring will be male (XY). So it is the male who is responsible for determining the sex of a baby. But still today there are cases of domestic violence like torturing a woman for producing a female child.
Twins
Occasionally two eggs are released by the ovary and fertilised. This results in fraternal twins who are different in appearance and may be of different sexes because their genes form from two eggs and two sperm cells. Rarely, one embryo splits into two and both cells develop separately, as identical twins, similar in appearance.
Implantation
After fertilisation the single cell splits into two, then the two cells double to four, four to eight, eight to sixteen and so on. Because the cell cluster looks superficially like a berry it is called the morula (Latin for “mulberry”).The journey along the Fallopian tube continues slowly for about four days. Growth increases. By the time the womb cavity is reached, the cell cluster becomes hollow and fluid-filled, and is referred to as the blastocyst. Meanwhile the uterus is forming a spongy lining within which the embryo will implant. To achieve this the embryo burrows into the wall of the womb and is covered over by the lining of the womb. This begins 6 days after fertilisation and is completed within the next 7 days. If fertilisation has not taken place, the lining of the uterus comes away at the end of the monthly cycle as the woman’s menstrual period. But once implantation occurs, the embryo sends out a hormonal signal which prevents the mother’s period. This is usually her first indication of pregnancy.
Body development
Determining the age of pregnancy
Generally a woman does not know the exact date of her baby’s conception. When she misses a period she may take a pregnancy test; she should see a doctor promptly to obtain professional care for herself and her child. The doctor takes the date of the first day of the mother’s last menstrual period as the starting-point for a 40-week pregnancy. This gives the baby’s gestational age. However since fertilisation only occurs when the ovum is released from the ovary, some two weeks from the beginning of the last period, the baby’s actual (conceptional) age is also two weeks less. Full-time delivery occurs 38 weeks after fertilisation, but 40 weeks after the mother’s last menstrual period.
Second month
The egg, or ball of cells, is now officially an embryo . It is only one-tenth of an inch long and its cells are in three distinct layers. The outer layer forms complex structures such as the brain and nerves and simple things such as hair and tooth enamel. The middle layer will turn into bones, muscles, blood vessels, and the heart, as well as part of the lungs. The inner layer forms the liver, intestines, urinary tract, and the other part of the lungs. A tuck forms at each end of the embryo: one will be the head and the other will be the one that wears the diapers.
Around the time the embryo is six weeks old, tiny bumps are forming that will be the arms and legs and vital organs like the stomach and lungs find their places. The two parts of the heart, which had developed separately, fuse then begin to beat. Also during this time the umbilical cord is forming, which is attached to the uterus at one end and the baby’s navel at the other end. This is the lifeline that provides the baby with nourishment.
By the end of the second month the embryo starts to look more human. The eyes stem out from the brain and place themselves on the face and the baby’s webbed hands begin to separate to form fingers. With the eyes still on either side of the head and not in front, though, the little tyke still looks like an alien from The X-Files, though.
Nourishment and protection of the baby in the womb
During and after implantation, the embryo develops a protective, fluid-filled capsule which surrounds and cushions the developing body to prevent injury. Embryo and fluid are enclosed in two membranes, an inner amnion and an outer chorion. The chorion is covered in rootlike tufts, some of which form the early placenta – an organ made by the baby and the mother which transfers nutrients from the mother’s bloodstream and removes waste products from the child’s, though mother’s and baby’s circulatory systems remain separate. The placenta also produces hormones to maintain the pregnancy. In the ninth month it will alter the mother’s hormonal balance and triggers off the birth process – although we are still unsure what causes labour to begin. The baby is connected to the placenta by the umbilical cord, the lifeline channelling nourishment in and taking wastes out, which will be cut close to the baby’s abdomen at birth and will leave the mark of the navel. During pregnancy the baby obtains oxygen from the mother’s blood via cord and placenta, so does not drown in the surrounding fluid.
Growth of various body parts
The embryo increases in size from 5mm at four weeks to 40mm by the end of the eighth week. The baby in the womb is usually measured from the top of the head to the bottom of the spine (crown-rump lengths).
By the sixth week from fertilisation, tiny fingers appear, followed within days by the toes. By the seventh week the baby develops individual fingerprints. No two sets of fingerprints are ever the same. Even in uterus the baby has unique characteristics.
By six weeks the eyes which appeared in simple form in the first month develop lens and retina; the eyelids start to take shape.
The ears continue to develop. By the seven week, the outer ear is present, and the inner ear, with its hearing and balancing mechanisms, is well established.
Response to touch
Human embryos of five weeks gestational age have been seen to move away from an object touching the mouth area. The sensitive area extends to include the rest of the face in the sixth and seventh weeks and the palms of the hands and soles of the feet in the eighth and ninth weeks respectively.
The Third Month
With the beginning of the third month or at the end of the first trimester, all the major internal organs starts developing. By the middle of the month testes develops in boys and the ovaries in girls. However, the external sex organs are still indistinct. Even at this stage it is not possible to determine the sex, even with the best ultrasound available.
Development of Embryo to foetus
After eight weeks the baby’s cartilage skeleton begins to turn into bone. The body is almost complete now. When the age of the embryo hits nine weeks, it is no longer considered an embryo. In this landmark week, it is officially a “f0etus”/”fetus”. The foetal umbilical cord is fully formed at this point and contains two large blood vessels: one huge artery and one huge vein. The cord is very stiff, tightly filled with blood, this is to avoid any kinks from forming; such an event could be fatal to the little one.
By the end of the twelfth week the baby measures almost 90mm and weighs 45g. At this stage of development, eyelids form over the eyes. After this happens, the eyes remains closed during most of the remainder of gestation.
Sensitivity of the child
Brain cells which are essential for consciousness in the adult are present in the foetus by 10 weeks. Nerve fibres which transmit pain impulses are present before fibres inhibiting pain are completed. The brain and nerve cells functions for the feeling of pain in an organism.
The Fourth month
During this month fingernails begin to form on the newly-shaped fingers, the gallbladder begins to make bile, and the baby makes its very own blood with its own bone marrow. By the middle of this month the external sex organs become distinctly male or female. All types of hair begin to form, including hair on the head, eyelashes, eyebrows, and a fine downy hair that covers the entire body called lanugo. This unique hair grows all over the body in swirly patterns and disappears shortly after birth. By sixteen weeks the baby measures 140mm from crown to rump, just over one third of the size he or she will be at full term, and weighs around 200g. The heart now pumps 30 litres of blood a day.
Hearing/ Response to sound
There is evidence that from four months the foetus responds to sound. Doctors testing unborn children for deafness, while monitoring their reactions to noise with ultrasound (a technique for visualising the children in utero), have observed eye movements and “blink-startle” responses in foetuses of 16 to 32 weeks gestation.
The baby hears sounds from the outside world as well as from the mothers heart and digestive system: “In fact the inner ear of the foetus is completely developed by mid-pregnancy, and the foetus responds to a wide variety of sounds. He is surrounded by a constant very loud noise in the uterus – the rhythmical sound of the uterine blood supply punctuated by the noises of air passing through the mother’s intestine. Loud noises from outside the uterus such as the slamming of a door or loud music reach the foetus and he reacts to them.
The Fifth Month
After 20 weeks the baby is 190mm from crown to rump and weighs 460g. The muscles and limbs, which are much stronger this month than the last, give the baby the ability to move around to explore this little world, as well as push and kick at things. If the baby’s thumb gets close enough to its face, it grabs it and begins sucking on it. This instinct is for when, after birth, it is ready to breastfeed. Inside the intestines the baby’s first stool, called meconium, forms. And if the baby is a girl she begins to develop her own eggs, which, decades later, will possibly begin this life cycle again.
A baby born during the 22nd week has a 14.8 percent chance of survival. And about half of these survivors are brain-damaged, either by lack of oxygen (from poor initial respiration) or too much oxygen (from the ventilator). Neonatologists predict that no baby will ever be viable before the 22nd week, because before then the lungs are not fully formed.”
The Sixth Month
After 26 weeks, the foetus is 14″ long and almost two pounds. The lungs’ bronchioles develop and interlinking of the brain’s neurons begins. The higher functions of the foetal brain turn on for the first time. Some rudimentary brain waves indicating consciousness can be detected. It is during this month that bones harden, growth and weight gain are rapid, and others can feel the baby move. The only other significant thing this month is, even though the baby will not need to use them until the moment of birth, the lungs become fully-formed and ready to breathe.
The Seventh Month
At this stage the baby is 16″ long and weighs about three pounds. Regular brain waves are detectable which are similar to those in adults. Things get even more cramped this month as the baby continues to grow. It goes into the typical foetal position with its legs bent into its chest. The baby is very active during this month; indeed, as the mother lies in bed at night, she might actually see her whole stomach change shape as her baby shifts its position. During this month the eyelids, which formed in the second month, begin to open, awakening the baby’s sense of sight. Now it can see as well as it can hear. The brain also rapidly grows, becoming folded and wrinkled; each section is assigned its duty, like controlling speech or recording memories. If the baby is a boy, the testicles, which had formed in the abdomen, will begin to move down to the scrotum.
The Eighth Month
At this stage the baby is18″ long and weighs about 5 pounds. At this stage the baby is preparing to pack up and move out . If a baby is born at this stage it has pretty good chances of surviving. The baby gets lots of antibodies from the mother’s immune system this month to protect it from a plethora of diseases that could infect it after birth. But this is only a temporary immunity which goes away after birth. However, the length of this immunity can be extended by breastfeeding. Also, even though it cannot breathe on its own yet, it will hiccup.
The Ninth Month
Now the baby is 20″ long and with an average weight of 7 pounds, a full-term foetus is typically born about this time. Growth finally begins to slow as the baby is ready to get out.
Labour and Delivery
In the last weeks of pregnancy the baby lies head downwards, as the head is normally the first part to emerge at birth. The baby moves into a position he or she will take during delivery. Even though what exactly triggers labour is still a mystery, it will eventually happen. The mother’s labour begins as (following hormonal signals including that from the placenta) the muscular uterus contracts to expel the baby. The cervix (neck of the womb) gradually opens to allow the baby to pass into the vagina (birth canal). The amnion tears and releases its fluid (this is often referred to as “the waters breaking”). Contractions become more frequent as the baby is pushed through the cervix and vagina.
After labour, which varies in length but usually lasts some hours, the baby is born. A gasp and a cry start the lungs working. The umbilical cord is cut and the baby is examined and weighed. Normal birthweight is approximately 3,400 grammes or about 7½ lb. Finally the membranes and placenta are expelled. The baby no longer needs a direct life support system as he or she can now breathe air and take milk.
