Overview of normal development of the fetus with associated clinical significance Objectives to review the clinical aspect associated with normal development the fetus and their significance so the student become well acquainted with clinical signs and symptoms of pregnancy

IMPLANTATION AND EARLY DEVELOPMENT OF OVUM The ova is fertilized in the ampullary region of the tube After 24 rest starts to divide rapidly foring morula and blastocyst At day 8-9 it reaches the endometrial cavity There implantation may occur any where The endometrium is re named as decidua of which there are 3 types Decidua baslis Decidua capsularis And decidua parietalis Obliteration of the endometrial cavity occurs when deciua capsularis fuse with decidua parietalis

Early implantation stage The chorion is a specia tissue which starts to develop also surrounding the fetal sac The part surrounding the amniotic cavity is called chorion The part bellow the fetus is called chorion frondosum The last is the part which is responsible for the placental development Chorion is composed of 2 layers Inner of columnar cells which gradully degenerate ; called cytoblast The outer is a mass of cytoplasm and huge number of nuclei called syncitioblast The later plays important role in development of the placenta A heap of cells appears in the blastocyst called fetal pole from which fetus develop

Hormonal changes Once the placenta is formed even before full maturity starts to secret 4 hormones 1 estrogen- esteriol Progesterone Human placental lactogen which ensures good supply of nutrients to the fetus HCG or human chorionic gonadotrophin which reaches maximum level at 6-8 weeks And disappear at 16-18 weeks It supposrt corpus luteum of pregnancy until placenta produce its own amount of progesterone at 12 weeks of gestation

While changes in the blastocyst occur Inner cell mass starts to form ectoderm and endoderm This primitive fetus undergoes folding so the endoderm lies inner ward while ectoderm lies outer hood Endoderm forms all GIT tract while ectoderm forms skin and nervous system In between a layer of mesenchymal tissue start to appear through which cavities appears which becomes peritoneal cavity and pleural cavity The yolk sac has no role in mammalian and usually degenerate early unlike in other vertebrates

DEVELOPMENTAL EVENTS OF THE FIRST TRIMESTER The fetus in the first 12 weeks is highly susceptible to toxins, drugs, radiations and even hormonal insufficiency and many cycles may be passed without the mother aware she is pregnant At the stage where inner cell mass undergoes primary differentiation to 3 layers huge changes occur in which at 10 weeks full adult organs are well developed Brain records of encephalography is perceivable at 11 weeks HCG starts to appear in blood tests at 5 days after implantation while 2 weeks in urine after implantation Morning sickness occurs virtually in all women yet with great variability in severity Embryo changes its name to fetus when fully developed head ad lower legs develop usually 59 day after fertilization corresponding to 30 mm in length

DEVELOPMENTAL EVENTS OF THE FIRST TRIMESTER Fetal heart rate may be shown first at 6 weeks after fertilization by trans abdominal U/S While by vaginal U/S scan fetal heart rate may shown as early as 4 weeks after fertilization due to the higher resolution of the U/S device The primary areola becomes deeply stained while a second areola starts to appear surrounding the primary and disappear after 6 weeks after dekiver In addition special tubercle like projections starts to appear in the primary areola called Montgomery’s tubercle They correlates highly pregnancy and this may help the physician to differentiate between many causes of acute abdomen with ectopic pregnancy like twisted ovarian cyst or appendicitis In addition a dark shaped line appears centrally bellow the umbilcus called linea nigra

Normal development in the second trimester The uterus become palpable per abdomen suprapubic Fetal quickening may be fetal 18-20 weeks of gestation The mother weight starts to increase throughout pregnancy average=12 kg Fetal weight bypass placental weight at 16 weeks Physiological anemia starts to appear from hemo dilution The breast may secret a fluid which is clear and yellow in color called colostrums Fetal heart rate may be audible by the old PINARD stethoscope The fetus starts to show response to acoustic stimuli The gesture of mother starts to change during standing due to lumbar lordosis HCG should become negative after 20 weeks Alpha fetoprotein starts to appear in the blood Maternal cardiac output increase with increase in plasma volume by 40 percent and RBC 20 % All clotting factors also increase except 11 ad 13 during the rest of pregnancy

Fetal changes in the third trimester Lanugo hair and vernix caseosa The pregnancy complication like hypertension After 37 weeks the head becomes presenting Increase in hemo dilution and cardiac output Blood supply to placenta 20% The pelvic maternal joints start to loose and hyper mobility In male fetal testis descend to scrotum via gubernaculums Cervix tend to become soft in texture Vaginal appear blue in examination Colostrums ,may increase toward delivery and contains IgG Milk starts to secrets 2 days after delivery Lordosis and waddling movement is a rule Amniotic fluid reaches maximum at 35 weeks and reduce there after Involuntary loss of urine may occur Labor cause in human is unknown , fetus may pay role in its onset