1. The document discusses fetal development from fertilization through birth, dividing it into the preovular period, embryo period, and fetal period. 2. Key events include fertilization, implantation, embryogenesis, and fetal growth through weeks of gestation. 3. Fetal circulation is described, which changes after birth when the umbilical cord is cut.

1. Dr Ravikanth G O
Associate professor
Dept of OBG
KVG Medical College

2. Embryo or fetus gestatesduring pregnancy from
fertilization until birth.
It is also known as fetal development orembryology.
Development biology is the study of the sequences of
events from the fertilization of a secondary oocyte bya
sperm cell to the formation of an adultorganism.

4. Age of thefetus
Gestational age is the duration of pregnancycalculated
from the first day of last menstrual period (LMP).
It is greater than the post conception (fertilization)age
by 2weeks.

5. Pre embryonic
period
Ovular period or germinalperiod.
Embryogenesis start with the fertilization of the egg cell
(ovum) by a sperm cell (spermatozoon). zygote,
a single diploid cell.

6. Fertilizatio
n

8. During the first week the zygote travels along the
uterine tube towards the uterus, the zona pellucida
surrounds the zygote. It nourished by glycogen
secreted by globlet cell of uterine tube and laterthe
secretory cells of uterus.
The zygote undergoes mitotic cellular replication
refered as cleavage, resulting into the formation of
smaller cells known asblastomeres.

10. The zygote divides into two cells- at 1stday
4 cells –at2 days
8by –2.5 days
16cells by- 3days. Known as morula.

11. Compaction.
Cavitation blastula 58 cells.

13. Implantation .
The blastocyst possesses an inner cell mass or
embryoblast and outer cell mass or Trophoblast.
Trophoblast- becomes the placenta andchorion.
Embryoblast- become embryo, amnion and umbilical
cord.

14. Trophoblast
Differentiate into two layers
syncytiotrophoblast
cytotrophoblast

15. Embryobla
st
Develops the embryo, and differentiate into two typesof
cells-
Epiblast- epiblast have three layers, which forms the
particular parts of the embryo. The first appearance
of these layers, collectively known as the primitive
streak is around 15days.
Hypoblast- the hypoblast cell migrate along with
inner cytotrophoblastic lining secreting extracellular
tissue which becomes the yolk sac.

16. Development by weeks of
gestation
1. Pre embryonicperiod-
Week 1-2
Week 3

17. Week 4th – days 22-28fromLMP
embryonic age 2weeks-
Events-
 Trophoblast - placenta and embryonic
membrane.
 Formation of yolk sac.
 Primitive streak develop at 13days.
 Primary stem villi appears at 13days

18. Week 5
Gestational age: 4 weeks
Embryonic age: Week no. 3
A notochord forms in the center of the embryonic
disk. (day 16of fert.
Gastrulation commences. (day 16of fert.)
A neural groove (future spinal cord)forms over the
notochord with a brain bulge atone
end. Neuromeres appear. (day 18of fert.)
Somites, the divisions of the future vertebra, form.
(day 20of fert.)
Primitive heart tube is forming. Vasculature begins to
develop in embryonic disc. (day 20of fert.

21. Week 6- gestational age-5 week
embryonic age 4weeks
Events –
 Embryo measures 4 mm
 The heart bulge, n begins to beat in a regularrhythem.
 The neural tube closes.
 Arm buds and tail arevisible.
 Pulmonary primordiumappear
 Hepatic plate appear
 Buccopharyngeal membrane ruptures. This form the
future mouth.
 Anterior and posterior horns differentiate in thespinal
cord.

23. Week 7-
embryonic age 5week
Events-
Length is 9 mm
Lens pits and optic cupsdevelops
Nasal pits form
Brain divides into 5vessicles including the early
telencephalon.
Leg buds form.
The metanephros, precursor of kidney start todevelop.
Stomach differentiation begins.

25. Week 8-
The embryo measures 13mm (1/2 inch) inlength.
Lungs begin to form.
The brain continues todevelop.
Arms and legs have lengthened
with foot and hand areasdistinguishable.
The hands and feet have digits, but may still be
webbed.
The gonadal ridge begins to beperceptible.
The lymphatic system begins todevelop.
Main development of external genitaliastarts.

26. Week 9-
The embryo measures 18mm (3/4inch) in length.
Fetal heart tone (the sound of the heart beat) can be
heard using doppler
Nipples and hair follicles begin to form.
Location of the elbows and toes arevisible.
Spontaneous limb movements may be detected
by ultrasound.
All essential organs have at least begun.
The vitelline duct normallycloses

27. Fetal
development
From the 10weeks of gestation (8th week of
embryogenic) the developing organism is called fetus.
All the major structures are already formed in the fetus
but they continue togrow.

28. Week 10 -
12
Embryo measures 30–80mm (1.2–3.2inches) inlength.
Intestines rotate.
Facial features continue to develop.
The eyelids are moredeveloped.
The external features of the ear begin to take their final
shape.
The head comprises nearly half of the fetus' size.
The face is well formed
The eyelids close and will not reopen until about the 28th
week.
Tooth buds appear.
The fetus can make a fist with itsfingers.
Genitals appear well differentiated.
Red blood cells are produced in the liver

30. Week 13-16-
The fetus reaches a length of about 15cm (6inches).
A fine hair called lanugo develops on thehead.
Fetal skin is almost transparent.
More muscle tissue and bones have developed, and the
bones become harder.
Sucking motions are made with the mouth.
Meconium is made in the intestinal tract.
The liver and pancreas produce fluid secretions.
From week 13,sexprediction
At week 15,main development of external genitalia is
finished
Abdominal wall closes.

31. Abdominal wall
defects

33. Week 17-
21
The fetus reaches a length of 20cm (8inches).
Lanugo covers the entirebody.
Eyebrows and eyelashes appear.
Nails appear on fingers andtoes.
The fetus is more active with increased muscle
development.
"Quickening" usually occurs (the mother and others
can feel the fetus moving).
The fetal heartbeat can be heard with astethoscope.

35. Week
23-
The fetus reaches a length of 28cm (11.2 inches).
The fetus weighs about925g.
Eyebrows and eyelashes are well formed.
All of the eye components aredeveloped.
The fetus has a hand and startlereflex.
Footprints and fingerprints continue forming.
Alveoli (air sacs) are forming in lungs.

36. Week
27
The fetus reaches a length of 38cm (15inches).
The fetus weighs about 1.2kg.
The brain develops rapidly.
The nervous system develops enough to control some
body functions.
The eyelids open andclose.
The respiratory system, while immature, has
developed to the point wheregas exchange is possible.

38. Week
31
The fetus reaches a length of about 38–43cm (15–
17 inches).
The fetus weighs about 1.5kg (3lb 0oz).
The amount of body fat rapidlyincreases.
Rhythmic breathing movements occur, but lungs are not
fully mature.
Thalamic brain connections, which mediate sensory input,
form.
Bones are fully developed, but are still soft andpliable.
The fetus begins storing a lot
of iron, calcium and phosphorus

39. Week
35
The fetus reaches a length of about 40–48cm (16–
19 inches).
The fetus weighs about 2.5to 3kg (5 lb 12oz to 6 lb 12
oz).
Lanugo begins to disappear.
Body fat increases.
Fingernails reach the end of the fingertips.
A baby born at 36weeks has a high chance of survival,
but may require medical interventions

40. Week 36-
40
The fetus is considered full-term at the end of the 39th
week of gestational age.
It may be 48to 53cm (19to 21inches) inlength.
The lanugo is gone except on the upper arms and
shoulders.
Fingernails extend beyond fingertips.
Small breast buds are present on bothsexes.
Head hair is now coarse and thickest

42. Fetal circulation

43. Fetal circulation changes
afterbirth

44. Summary
Preovular period
Embryo period
Fetal period
Fertilisation
Implantation
Embryogenesis
Fetal growth
Fetal circulation
Changes in fetal circulation after birth