Fetus Growth Stages: Let us discuss the development weeks of fetus growth stages from the period of conception of birth.
0-4 weeks after conception’
- Rapid growth
- Formation of the embryonic plate
- Primitive cental nervous system forms
- Heart develops and begins to beat
- Limb buds form.
- By end of 4 weeks embryo has assumed SALAMANDER look and has rudiments of ears (otic Pit), arms (arm buds) legs (leg buds) and facial and neck structures.
Fetal heart rate at 8 weeks
- Very rapid cell division
- Head and facial features develop
- All major organs are present in their earliest form.
- External genitalia present but sex not distinguishable.
- Early movements.
- Visible on ultrasound from 6 weeks.
- Eyes begin to develop.
- During 6th week nose, mouth and palate begin to take from eyelids become visible end of 7th week embryo has districtly human characteristics.
- At end of 7th week embryonic period ends.
- The formation of all necessary internal and external structures.
- It is a critical period during where any teratogen (drugs, X-ray, Viruses may either be letthal (deadly) or cause major cogenital malformation.
Fetal heart rate at 10 weeks | fetal heart rate 190 at 9 weeks
- Eyelids fuse
- Kidneys begins to function and the fetus passes urine from 10 weeks
- Fetal circulation functioning properly
- Sucking and swallowing begin
- Sex apparent
- Moves freely (not felt by mother)
- Some primitive reflexes present.
- Fetus now looks undeniably human.
- Fetus at this stage weights 0.5-1ounce.
- Fetuis can swallow make respiratory movement urinate open or shut his/her mouth.
- X-rays show rapid skeletal development Meconium is seen in the intestines.
- Lanugo appears
- Nasal septum and palate fuse.
- Head grows slowly
- Ears move to a higher elevation on sides of head.
- Chin becomes evident.
- Eyes remain closed.
- Reflex response and muscular activity week begins.
- Sex in clearly distinguishable by 14th week.
- Bone development takes place and could be seen by roentgenography.
- Average crown-rump (top of head to buttock length = 11.5cm (4.5 inches)
- Fetus weights between 99-113 in (3.5-4 ounces) bye edning 16th week
17 -20 weeks
- ‘Quickening’-mother feels fetal movements
- Fetal heart heard on auscultation
- Vernix caseosa appears
- Fingernails can be seen
- Skin cells begin to be renewed.
- Rapid body growth countinues.
- Legs reach their full length.
- Eyelids remain fused.
- Fetus moves freely inside the uterus.
- The fetus hiccups and mother may fed it as a series of slight rhythmic series or
- At end of 20 week average crown-rump length of fetus = 16.5cm (6.5 inches) and average weight is almost 341 gm (0.75 lbs)
- Most organs become capable of functioning
- Periods of sleep and activity
- Responds to sound
- Skin red and wrinkled.
- Fetus completely covered with lanugo.
- Eyebros, eylashes and head hair are present.
- Head remains large as compared to the rest of body.
- Skin is wrinkled and red, gusing and aged appearance to the fetus.
- Buds for permanent teeth are present.
- The fetus being small has room in uterus to somer soult (turns head over head) and can make motions of crying and sucking.
- Hands make fests.
- Brown fat forms.
- Average crown rump length = 20 cms (8 inches) and average weight = 568 gm (1.25 lbs)
- Survival may be expected if born
- Eyelids reopen
- Respiratory movements present.
- Sucking reflex is stronger.
- Fingernails are present.
- The average crown-rump length is approximately
- 22.5 cm (9 inches) and weight is about 1023 gm (2.25 lbs) by end of 28th week.
- Survical may be expected if born.
- Begins to store fat and iron
- Testes descend into scrotum
- Lanugo disappears from face
- Skin becomes paler and less wrinkled.
- Thick vernix caseosa covers the whole body.
- Fetus has control of rhythmic breathing and body temperature.
- The average crown-rump length is about 27.5 cm (11 inches) and weight approximately 1.7 kg (3.7 lbs)
- The body becomes rounder with additional fat on it. Lanugo leaves the body.
- Head hair lengthens
- Nails reach tips of fingers
- Ear cartilage soft
- Plantar creases visible.
- Skin is smooth without wrinkles.
- Baby is rounder, hair larger.
- Left testicle has usually descided into sceotum.
- Plantar creases are visible.
- Average crown-rump length is a little over 31 cm (12.5 inches) approximately 2.5 kg (5.5 lbs) in the 36th weeks.
- 37-40 weeks after conception (38-42 weeks after LMP)
- Fetus receives finishing touches during this period.
- Fetus is well round and Protuberant mammary glands in both sexes.
- Term is reached and birth is due
- Contours rounded
- Skull form
- Both testes are scrotum
- Skull is firm
- Skin varies in color from culute to pink to bluish pink regardless of race because the melonin that colors the skin in produced only after exposure to light.
- The crown-rump length now averages 31 cm (14 inches)
- Average weight is 3.2 kg (7lbs)
The fetal heart originates from the splanchnic mesoderm and first appears as two tubes that eventually merge and then canalise. Then there are repeated rotations and septations, which eventually produce a four-chamber organ. In fetal heart circulation the embryo develops a separate fetal circulation from the 16th post-fertilization day. Fetal heart starts beating from 21day of fertilization. Simultaneously the fetus in utero derives Oxygen and nutrients from placenta as its lungs and alimentary tract are functionless. So, fetal circulation is the circulation through which the fetus receive oxygen and nutrients for its survival through the placenta.
Fetal Heart Circulation
- From Placenta Single Umbilical Vein in Umbilical Cord
- Carries Oxygenated blood 80%
- Goes to liver through fetal Umbilicus
- Then it branches into 2, One large branch & one small branch (O2 Saturation of blood at IVC before entry of heart is 65%)
- Large branch (ductus venous-from a vein to vein by passes (first by pass) the liver.
- Enters the Inferior Vena Cava (i.e. mixing with venous blood from inferior extremity)
- goes to right atria of heart
- 75% of blood from right atria
- Goes to left atria (through foramen ovale)
- Left ventricle
- Coronary arteries and aorta
- From aorta blood with 60% O2 saturation is pumped to head neck and superior extremities.
- 25% of blood in right atrium mixes with blood from superior vena cava
- Draining head neck and upper extremities
- Enters right ventricle
- Pumped to pulmonary artery
- This blood goes to collapsed lungs in small part
- It is drained back into left atria by pulmonary veins
- Its large part goes to
- Descending Aorta
- Abdominal Aorta
- Supplies main body organs and the legs So,
- The major part of blood from abdominal Aorta
- Goes to 2 internal illiac arteries and 2 hypogastric arteries
- These arteries run towards umbilicus
- Enter the cord as 2 umbilical arteries which carry venous blood to the placenta for purification.
Changes of Fetal Heart Circulation After Birth
The haemodynamics of the fetal circulation undergoes profound changes soon after birth due to:
(a) Cessation of the placental blood flow.
(b) Initiation of respiration. The following changes occur in vascular system:
- CLOSURE OF UMBILICAL ARTERIES
(a) Functional closure is almost instantaneous preventing even small amount of fetal blood to drain out.
(b) Actual Obliteration takes about 2-3 months. (c) Distal parts of Umbilical arteries form lateral umbilical ligaments.
(d) Proximal parts remain open as superior vesical Arteries.
- CLOSURE OF UMBILICAL VEIN
(a) Obliteration occurs a little later than the arteries allowing few extra volumes of blood (80-100ml) to be received by the fetus from the placenta.
(b) The ductus venosus and venous pressure of inferior Vena Cava fall and so the right atrial pressure.
(c) After Obliteration, the Umbilical vein forms the ligamentom teres and ductus venous becomes ligamentum venosum.
- CLOSURE OF DUCTUS ARTERIOSUS
(a) Closure of ductus arteriosus occurs after establishment of pulmonary ventilation.
(b) Rise in O, content stimulates its closure ductus arteriosus becomes ligamentum arteriosum.
(c) Anatomical Obliteration takes about 1-3 months.
- CLOSURE OF FORAMEN OVALE
(a) This is caused by an increased pressure of left atria combined with a decreased pressure on the right atrium.
(b) Functional closure occurs soon after birth.
(c) Anatomical closure occurs about 1 year time.
(d) Closed foramen ovale gives fossa ovalis
So, within one on or two hours following birth neonatal heart pumps 500ml blood per minute through 120-140 beats.
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