Neonatal Anatomy
The branch of science dealing with the structure of new born baby (up to four weeks old after birth), is referred to as neonatal anatomy.
Neonatology
The branch of science which deals with the study, care, and treatment of neonates, is known as neonatology.
Prenatal period
The time existing before birth, is known as prenatal period.
Postnatal period
The time occurring after birth, is known as postnatal period.
Postpartum
It is relating to the period of a few days immediately after birth.
Embryo
- An animal at an early stage of development, before birth, is known as embryo.
- In human the term refers to the products of conception within the uterus up to the eighth week of development, during which time all the main organs are formed.
Fetus
A mammalian embryo during the later stages of development within the uterus is referred to as fetus.
In human reproduction it refers to an unborn child from its eighth week of development.
Differences between embryo and fetus
| Sl. No. | Embryo | Fetus |
| 1 | In human the term refers to the products of conception within the uterus up to the eighth week of development, during which time all the main organs are formed. | In human reproduction it refers to an unborn child from its eighth week of development. |
| 2 | It begins after fertilization. | It begins on the first day of 3rd month. |
| 3 | It develops during the embryonic period (the shortest period). | It develops during the fetal period (the longest period). |
| 4 | A human embryo is not considered viable, because it cannot survive outside the uterus. | The lower limit of viability is approximately five months gestational age, and usually later. |
| 5 | An embryo can be transplanted from the uterus of one woman to that of another. | It cannot be transplanted to others. |
| 6 | Here RBC is formed in the yolk sac and mesothelial layers of the placenta (3rd week), from the liver (6th week), spleen and other lymphoid tissues (3rd month). | Here bone marrow develops (5th month) and blood begins to form within it. |
Gestation
In mammal, gestation means the length of time from conception to birth. In humans, the average length, as calculated from the 1st day of the last normal menstrual period, is 280 days, with a normal range of 259 days (37 weeks).
Parturition (childbirth)
Parturition means the act of giving birth to young. It consists of the ejection of baby with afterbirth (placenta) from the uterus.
Gynecology
It refers to the study of the diseases of the female reproductive organs and the breasts.
Obstetrics
It is the branch of medical science concerned with the care of women during pregnancy, childbirth, and the period of about six weeks following the birth, when the reproductive organs are recovering.
Development of the organ system
Within one month after fertilization the organs of the fetus have begun to develop. During the next two or three months the different organs are established. Beyond month 4, the organs of the fetus become almost same as those of the neonate. But the cellular development of the organs can take about 5 months or more of pregnancy.
Circulatory System. The heart begins to beat during the fourth week after fertilization, which is about the same time that the first non-nucleated red blood cells form. During the first two thirds of gestation, red blood cells are formed outside the bone marrow; only during the final 3 months of gestation are most of the red blood cells formed in the bone marrow.
Respiratory System. Although some 'respiratory movements take place during the first and second trimesters, respiratory movements are inhibited during the final 3 months of gestation. This inhibition prevents filling of the lungs with debris from the amniotic fluid.
Nervous System. The organization of the central nervous system is completed in the first months of gestation, but full development and even complete myelination do not take place until after delivery.
Gastrointestinal Tract. By midpregnancy, the fetus ingests amniotic fluid and excretes meconium from the gastrointestinal tract. Meconium is composed of residue from amniotic fluid and waste products and debris from the epithelium of the gastrointestinal tract. By the final 2 to 3 months of gestation, gastrointestinal tract function approaches maturity.
Kidneys. The fetal kidneys can form urine beginning in the second trimester, and urination takes place during the latter half of gestation. The ability of the kidneys to accurately regulate the composition of the extracellular fluid is poorly developed until several months after birth.
Causes of 2 weeks difference between two scales
In the 28 days of menstrual cycle, the ovulation occurs on 14th day. Then after sexual intercourse, the fusion of a spermatozoon and ovum occurs and forms zygote (called fertilization), and after 6 to 9 days of fertilization the zygote is implanted into the endometrium of uterus (called implantation).
In fine, the fertilization occurs on or after 2 weeks (14 days) of one complete menstrual cycle. Normally the gestation period is counted from the first day of the last menstruation to the childbirth. The first scale shows only the time limit from the fertilization period to the childbirth, not the full gestation period, which the second scale shows. So, the two scales differ from 2 weeks with each other. The physicians follow the second one as the pregnancy period.
Embryology
Embryology is the study of the developmental processes from the state of fertilized ovum to the stage of birth in human beings.
Fertilization
The process of production of diploid zygote by the fusion of a spermatozoon and ovum, is referred to as fertilization.
Implantation
It refers to the attachment of the diploid zygote to the lining of the uterus, which occurs at the blastocyst stage of development, six to nine days after fertilization.
Neonate
Neonate is an infant at any time during the first 28 days of life. The word is particularly applied to infants just born or in the first week of life.
Neonatal measurements and period of time in utero
The 10th to 90th centile ranges for length of full-term neonates are c.48 cm to c.53 cm Length of the newborn is measured crown to heel. In utero, length has been estimated either from crown-rump length, i.e. the greatest distance between the vertex of the skull and the ischial tuberosities, with the fetus in the natural curved position, or from the greatest length exclusive of the lower limbs. Greatest length is independent of fixed points and thus much simpler to measure. It is generally taken to be the sitting height in postnatal life. This measurement is recommended by O'Rahilly and Muller (2000) as the standard in ultrasound examination. The 10th to 90th centile ranges for weight of the full-term infant at parturition ranges are c.2700 g to c.3800 g , the average being 3400 g; 75-80% of this weight is body water and a further 15-28% is composed of adipose tissue. After birth, there is a general decrease in the total body water, but a relative increase in intracellular fluid. Normally, the newborn loses c.10% of the birth weight by 3-4 days postnatally, because of loss of excess extracellular fluid and meconium. By 1 year, total body water makes up 60'/o of the body weight. Two populations of neonates are at
particular risk, namely those who are preterm, and those who are small-for-dates, some of whom have suffered intrauterine growth restriction.
particular risk, namely those who are preterm, and those who are small-for-dates, some of whom have suffered intrauterine growth restriction.
Low birth weight has been defined as less than 2500 g,[very low birth weight less than 1500 g, and extremely low birth weight as less than 1000 g. Infants may weigh less than 2500 g but not be premature by gestational age. Measurement of the range of weights fetuses may attain before birth has led to the production of weight charts, which allow babies to be described according to how appropriate their birth weight is for their gestational age, e.g. small for gestational age, appropriate for gestational age and large for gestational age. Small for gestational age infants, also termed 'small-for-dates', are often the outcome of intrauterine growth retardation. The causes of growth restriction are many and various and beyond the scope of this text. For both premature and growth-retarded infants, an assessment of gestational age, which correlates closely with the stage of maturity, is desirable. Gestational age at birth is predicted by its proximity to the estimated date of delivery and the results of ultrasonographic examinations during pregnancy. It is currently assessed in the neonate by evaluation of a number of external physical and neuromuscular signs. Scoring of these signs results in a cumulative score of maturity that is usually within ± 2 weeks of the true age of the infant. The scoring scheme has been devised and improved over many years. For an account of methods of assessing gestational age in neonates, consult Gandy (1992).
References
1. Anatomy and Physiology, F. Evans, 2nd edition, New Jersey, Prentice-Hall, Inc.
2. Pocket Companion to Textbook of Medical Physiology, Guyton and Hall, 1998, India, Harcourt Brace Asia, Sauders.
3. Fundamentals of Human Anatomy, N. Chakraborty & D. Chakraborty, 1st edition, Calcutta, New Central Book Agency Pvt. LTD.
4. Ucchay Maddhomic Jibbiggyan (Zoology), Azmal & Asmat, 2004, Dhaka, Gazi Publishers.
5. Tabe’s Encyclopedic Medical Dictionary (vol. 1& 2), 20th edition, Philadelphia, F. A. Davis Company.
6. Dictionary of Pharmacy, Md. Ali, 2007-08, Delhi, Tara Publishers.
7. Concise Medical Dictionary, 6th edition, Oxford University Press, MSDict Viewer, v2.11
8. Wikipedia
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