MORPHOLOGIC DEVELOPMENT
During the first 2 weeks from the time of ovulation, there are successive phases of development that are identified as :
1. Ovulation
2. Fertilization of the ovum
3. Formation of free blastocyst
4. Implantation of blastocyst
5. Primitive chorionic villi formation.
It is conventional to refer to the products of conception after the development of chorionic villi not as a fertilized ovum but as an embryo.
The Embryo : The beginning of the embryonic period is taken as the beginning of the third week after ovulation and coincides in time with the expected time of menstruation. The embryonic disc is well defined and the body stalk is differentiated. At this stage, the chorionic sac measures approximately 1cm in diameter. By the end of the fourth week after ovulation the chorionic sac measures 2 to 3 cm in diameter and the embryo about 4 to 5 mm in length. The heart and pericardium are very prominent because of the dilatation of the chambers of the heart. Arm and leg buds are present and the amnion is beginning to unsheathe the body stalk, which thereafter becomes the umbilical cord.
At the end of the Sixth week from the time of ovulation, or about 8 weeks after the onset of the last menstrual period, the embryo is 22-24 mm in length and the head is quite large compared with the trunk. Fingers and toes are present, and the external ears form definitive elevations on either side of the head.
The end of the embryonic period and the beginning of the foetal period are arbitrarily considered by most embryologists to occur 8 weeks after ovulation or 10 weeks after the onset of the last menstrual period. At this time, the embryo is nearly 4 cm long. Few, if any, new major structures are formed thereafter ; development during the foetal period of gestation consists of growth and maturation of structures that were formed during the embryonic period.
CHARACTERS OF NEONATE :
The anthropometry of average term infant are :
Weight : 2.5-3.5 Kg.
Length : 50cm
Head Circumference : 34-35 cm
Chest Circumference : 31-32 cm
Mid arm circumference : 8 cm
Ratio between upper and lower segment : 1.7-1.9 : 1
Other characters of new born :
Attitude : Flexion
Cry : Vigorous
Sleep : 80% of time
Skin : Pink
Lanugo Hair : Upper back and dorsal aspect of limbs
Sclerae : Slight bluish
Ear cartilage : Firm, fully curved; Good elastic recoil
Breast nodule : Palpable
* Size - >5 mm
Soles : Deep creezes +
H.R. : 120-140/min
R.R. : 30-40 min.
Male:
Testes : Minimum 1 testes descend into scrotum
Scrotum : Deeply pigmented and has adequate rugae
Female :
Labia Majora : Covers the labia minora
FUNCTIONAL DEVELOPMENT ACCORDING TO MODERN MEDICINE :
I. NUTRITION :
There are three stages of foetal nutrition following fertilization.
1. Absorption : In the early post fertilization period, the nutrition is stored in the deutoplasm within the cytoplasm and the very little extra nutrition needed is supplied from the tubal and uterine secretion.
2. Histotrophic transfer : Following nidation and before the establishment of the utero placental circulation, the nutrition is derived from the eroded decidua by diffusion and lateron from the stagnant maternal blood in the trophoblastic lacunae.
3. Haemotrophic : With the establishment of the foetal circulation, nutrition is obtained by active and passive transfer from the 3rd week onwards.
While all the nutrients are reaching the foetus throughout the intrauterine period, the demand is not squarely distributed. Two thirds of the total calcium. Three fifths of the total proteins and four-fifths of the total iron are drained fromthe mother during the last 3 months. Thus, in preterm birth, the store of the essential nutrients to the foetus is much low.
II. FOETAL BLOOD :
1. Haematopoiesis is demonstrated in the embryonic phase first in the yolk sac. By 10th week, the liver becomes the major site. The great enlargement of the early foetal liver is due to its erythropoietic function. Gradually, the red cell production sites extend to the spleen and bone marrow and near term the bone marrow becomes the major site of red cell production.
2. In the early period, the erythropoiesis is megaloblastic but near term it becomes normoblastic. During the first half, the haemoglobin is of foetal type but from 24 weeks onwards, adult type of haemoglobin appears and at term about 75-80% of the total haemoglobin is of foetal type. Between 6-12 months after birth, the foetal haemoglobin is completely replaced by adult haemoglobin. The foetal haemoglobin has got a greater affinity to oxygen. It is also resistant to alkali in the formation of alkaline haematin. Rh-factor has been demonstrated in the foetal blood from as early as 38 days after conception.
Blood picture at term :
RBC - 5-6 million / cu.mm
Hb% - 110-150%
Reticulocytes - 5%
Erythroblast - 10%
Total foeto placental blood volume - 125 ml / kg body weight of the foetus.
Life span of foetal RBC - About 80 days
III LEUCOCYTES AND FOETAL DEFENCE :
Leucocytes appear after 2 months of gestation. The white cell count rises to about 15-20 thousand per cu.mm at term. Thymus and spleen soon develop and produce lymphocytes, a major source of antibody formation. The foetus, however, rarely forms antibody because of relatively sterile environment. Maternal IgG crosses the placenta from 12th week onwards to give the foetus a passive immunity which increases with the increase in gestation period.
IV URINARY SYSTEM :
By the end of first trimester, the nephrons are active to secrete urine. Near term, the urine production rises to 650 ml per day. However, Kidneys are not essential for survival of the foetus in utero but are important to regulate the composition and volume of liquor amnii.
V. SKIN
At 16th week, lanugo appears and near term, almost completely disappears.
Sebaceous glands appear at 20th week.
Vernix caseosa : The secretion of the sebaceous glands mixed with the exfoliated epidermal cells is abundantly present smearing the skin.
The horney layer of the epidermis is absent before 20th week which favours trnasudation from the foetal capillaries into the liquor amni.
VI GASTRO INTESTINAL TRACT :
As early as 16th week, the foetus swallows amniotic fluid. The meconium appears from 20th week and at term, it is distributed uniformly throughout the gut upto the rectum indicating the presence of intestinal peristalsis. In intra uterine asphyxia, the anal sphincter is relaxed and the meconium may be voided into the liquour amnii.
VII. RESPIRATORY SYSTEM :
In the early months, the lungs are solid. At 28th week, alveoli expand and are lined by cuboidal epithelium. At 24th week, lung surfactant related to phospholipids- lecithin and sphingomyelin appears. A lecithin : Sphingomyelin (L:S) ratio of 2:1 in the liquor amnii signifies full maturity of the foetal lung. Foetal cortisol is the natural trigger for augmented surfactant synthesis.
Breathing movements are identified by 11 weeks but are irregular until 20th week. Their frequency varies from 30-70 per minute and may be dependant on the maternal blood sugar concentration.
IX. FOETAL ENDOCRINOLOGY :
Foetal pituitary starts production of GH, ACTH, PRL and GnRH from as early as the 10th week. Vasopressor and oxytocic activity of the posterior pituitary have also been demonstrated. Foetal adrenals show hypertrophy of the reticular zone. The adrenal medulla produces small amount of catecholamines. Foetal thyroid synthesises small amount of thyroxine. Foetal pancreas secretes insulin from as early as 12th week. While the foetal ovaries remain inactive, the testicles mediate the development of the male reproductive structures.
X. FOETAL CIRCULATION :
The umbilical vein carrying the oxygenated blood (80% saturated) from the placenta, enters the foetus at the umbilicus and runs along the free margin of the falciform ligament of the liver. In the liver, it gives off branches to the left lobe of the liver and receives the deoxygenated blood from the portal vein. The greater portion of the oxygenated blood mixed with some portal venous blood, short circuits the liver through the ductus venosus to enter the inferior vena cava and thence to right atrium of the heart. The terminal part of inferior vena cava also contains the deoxygenated blood from the caudal parts of the foetus below the diaphragm. The amount of such draining venous blood is not large enough to vitiate the pure blood from the ductus venosus to a great extent.
In the right atrium, most of the blood is guided towards the foramen ovale by the valve of the I.V.C. and crista dividens and passes into left atrium. Here, it is mixed with small amount of venous blood returning from the lungs through the pulmonary veins. This left arterial blood is passed on through the mitral opening to the left ventricle.
Remaining lesser amount of blood (25%) after reaching right atrium via the S.V.C. and I.V.C. passes through the tricuspid opening into the right ventricle.
The left ventricular blood is pumped into the ascending and arch of aorta and distributes to all parts of the body. The right ventricular blood with low oxygen content is discharged into the pulmonary trunk. Since, the resistance in the pulmonary arteries during foetal life is very high, the main portion of the blood passes directly through the ductus arteriosus into the descending aorta bypassing the lungs where it mixes with the blood from the proximal aorta. The mixed blood is distributed by the descending aorta and leaves the body by way of two umbilical arteries to reach the placenta where it is oxygenated and gets ready for circulation. The mean cardiac output is comparatively high in foetus and is estimated to be 255 ml per kg per minute.
Modern science also accepts that foetal umbilicus is attached to the umbilical cord and umbilical cord to placenta which is mentioned alike in Ayurveda. But the only difference is, in Ayurveda, it has been mentioned that this placenta is attached to maternal heart, but according to modern science, the placenta is attached to uterine decidua and collects blood through villi.
