Development and birth of a human baby in detail. After sexual intercourse, if the sperms meet the egg then it is called fertilization. Within 24 hours after fertilization, the egg quickly divides into many cells. The embryo grows into a fetus by the 8th week of pregnancy. The total gestation period (pregnancy) is usually about 280 days. The development of a baby or fetus is divided into three trimesters which we discuss in detail later.
In females, the reproductive cycle cis omplete in 28 days. It is called the menstrual cycle. The Human menstrual cycle generally repeats every 28 days although there is considerable variation in different individuals or even within the same individuals at different times of her age. The end or complete stop of the menstrual cycle is called menopause after which the female stops producing the ova around at age of 50.
In the reproductive cycle, a group of oocytes releases eggs and these are called follicles after these follicles get matured they release into the ovary and it is called ovulation. It happens before the 2 weeks of the next menstrual cycle. The follicle cells, after releasing an egg, are modified to form a special structure called corpus luteum. This yellowish glandular structure starts secreting a hormone called progesterone. This hormone develops the endometrium and makes it receptive to the implantation of the zygote (placenta formation).
The corpus luteum starts degenerating if the fusion of sperm and egg does not take place. The progesterone secretion lessened. This results in the release of blood called menstruation. This stage lasts for 3 to 7 days.
If fertilization occurs, within 24 hours, the egg cells start dividing into many cells and form an embryo and then into a fetus and finally into a baby.
A genetic combination of male and female
Women have a hereditary makeup of genes, XX and men have the genetic makeup of genes XY. Sperm is either X or Y. Egg is X. If sperm X combines with egg X then it is a girl “XX” and if sperm Y combines with egg X then it is a boy “XY”.
Stages of development
The development of a fetus or baby is divided into three trimesters:
- First trimester (first 3 months)
- Second trimester ( next 4 months)
- Third trimester ( last 3 months)
The first trimester includes the first 3 months after fertilization. In the first three months, the group of cells divides more and more and grows into a fetus.
When the fertilized egg is growing in the first month it develops an amniotic sac around it which helps the growing embryo.
The fundamental or basic face is developing with large dark circles in the eyes. The mouth, lower throat, jaws, and blood cells all are in the development stage.
The small heart also develops and starts beating at the end of the fourth week which beats sixty-five minutes.
This month, the placenta develops in the mother’s womb. It is a flat organ. Its functions as a transfer of nutrients from the mother to the fetus. It also transfers waste material from the fetus to the mother
Length of the embryo: The embryo is about ¼ inch long by the end of the first month.
By the second month, fingers, toes, bone, digestive tract, and sensory organs begin to develop. Facial character or features are also in the growing stage. The neural structures also start developing. In the 6th week, the heartbeat is observed. At the end of the second month (8th week), the fetus takes the place of an embryo
Length and weight: The fetus grows about 1 inch. The weight of the fetus is 1/30 of an ounce.
In the third month, the hand, finger, toes and external ears are developed. The nails and teeth begin to develop. The reproductive organs are in the developing stage It is difficult to find the gender of a fetus in ultrasound.
At the end of the third month, the circulatory system, urinary system and liver are working properly. The fetus is wholly formed.
Length and weight: The fetus grows about 4 inches. The weight of the fetus is 1 ounce.
It is also called the middle period of pregnancy. The fetus develops facial details. The fetus flips and twirls in the uterus.
During this month, fingers, toes, eyebrows, nails, hairs, teeth and bones are well formed and dense. Doctors can identify whether the fetus is a girl or a boy by ultrasound.
Length and weight: At the end of the fourth month, the fetus grows about 6 inches. The weight of the fetus is 4 ounces.
During this month, the fetus feels to move over. The muscles are going to form. The hairs also grow on the head. The hairs are furthermore starting to grow on the shoulder and back and they shed on the end of the first week of the world’s life. The skin is covered with a substance called “vernix caseosa”. This is a kind of white and cheese-like substance which protects the fetus from amniotic fluid. This shed just before birth.
Length and weight: At the end of the fourth month, the fetus grows about 10 inches long. The weight of the fetus is about ½ to 1 pound.
During the sixth month, the fetus starts to open its eyes. The fetus can be observed now. The skin colour of the fetus is reddish and creased. The veins are also visible. The jerking motions of the fetus can be observed.
Length and weight: At the end of the sixth month, the fetus grows about 12 inches long. The weight of the fetus is 2 pounds.
During the seventh month, the amniotic fluid starts to decrease. The fetus is e to change its posture and can respond to light, sound etc. The fetus is now maturing itself. If the fetus is born premature then it can survive.
Length and weight: At the end of the seventh month, the fetus grows about 14 inches. The weight of the fetus is 2 to 4 pounds.
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It is the last period of pregnancy. The fetus in this trimester gains weight, fat that helps after birth.
During the eighth month, the fetus starts kicking. The lungs may still be immature. The fetus continues to mature. Internal structures are also forming. (Development and birth of a human baby in detail)
Size and weight: At the end of this month, the fetus grows about 18 inches. The weight is approximately 5 pounds or more.
Development and birth of a human baby in detail. During the ninth month, the fetus is maturing itself. It can respond to light, sound etc. It can see, close and open the eyes, flicker, move etc. The lungs are also completely mature at this point.
Size and weight: At the end of this month, the fetus grows about 17 to 19 inches. The weight is approximately 5 ½ to 6 ½ pounds.
It is the last month of pregnancy, labouring can occur at any time. The space is tight. The fetus changes its position and is prepared for birth.
Size and weight: At this time, the fetus grows about 18-20 inches. The weight of the fetus is approximately 7 pounds.
Placenta and role
When the placenta is founded, it secretes progesterone which maintains pregnancy. Any disturbance in its secretion may lead to premature birth or miscarriage.
Amniotic sac and role
The human embryo remains enclosed in an amniotic sac filled with protective amniotic fluid and shock absorptive.
During this period, the pituitary gland produces LTH( luteotropic hormone). Placenta also secretes human placental lactogen. Both these hormones stimulate mammary development in preparation for lactation.
Fetus formation and Organogenesis
From the beginning of the 3rd month of pregnancy, the human embryo grows into the fetus. Most of the organs are formed in the 12th week of pregnancy. The remainder of the gestation period is taken up the growth. (Development and birth of a human baby in detail)
Steps of birth:
Mother fetus interaction and Timing of birth
It was thought that hormonal activities within the mother i.e. decrease in progesterone level onset the birth. But recent evidence suggests that there is a high degree of fetal involvement in the timing of birth.
Role of Fetus pituitary and release of ACTH
The preliminary phase of birth is the result of the bases from the fetal pituitary. The ACTH released from the fetal pituitary stimulates the fetal adrenal gland to release corticosteroids.
Release of corticosteroids and production of oxytocin
Corticosteroids cross the placental barrier and enter the maternal blood circulation causing a decrease in progesterone production. The reduction of progesterone levels stimulates the pituitary gland to produce oxytocin hormone. This induced labour pains.
Steps of labour
The Contraction of the uterus wall. The release of oxytocin occurs in “waves” during labour and provides the force to expel the fetus from the uterus.
The cervix dilates and the uterine contractions spread down over the uterus and are strongest from top to bottom. Thus, pushing the baby downward leads to the delivery of the baby. The umbilical cord is ligated and the baby is released from the mother.
Within 10-45 minutes after birth, the uterus contracts and separates the placenta from the wall of the uterus and the placenta then passes out through the vagina. This is called after birth. Bleeding, throughout this period, is controlled by the contraction of smooth muscle fibres which surround all uterine blood vessels supplying the placenta.
The average loss of blood: The average loss of blood is about 0.35 Litres.
Development and birth of a human baby in detail