Fetal development

Prenatal development includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal development until birth.

1. Page 1 of 33

fe
FETAL DEVELOPMENT SHARMA





TO GET FURTHER MORE NOTES:
https://sharmanotes.blogspot.com/


Ganga Prasad V
M.Sc (N) in Child Health Nursing

FETAL DEVELOPMENT

2. Page 2 of 33

fe
FETAL DEVELOPMENT SHARMA
INTRODUCTION
 Prenatal or antenatal development is the process in which embryo or fetus gestates during
pregnancy from fertilization until birth. It is also known as fetal development or
embryology.
 Development biology is the study of the sequences of events from the fertilization of a
secondary oocyte by a sperm cell to the formation of an adult organism.
 Age of the fetus: Gestational age is the duration of pregnancy calculated from the first
day of last menstrual period (LMP). It is greater than the post conception (fertilization)
age by 2 weeks.

FACTORS AFFECTING FETAL GROWTH
 Genetic: Predominant control is genetic.
 Fetal sex: A male fetus weighs 100 to 200 gm more than a female at term.
 Race: European babies weigh more than Indian babies.
 Maternal age: Mothers over 35 years of age tend to have smaller babies. Incidence of
congenital anomaly is also higher.
 Socio-economic and nutritional: Average weight of babies born to lower social class
tends to be lower.
 Parental height and weight: tall and heavier mothers have heavier babies.
 Birth order: Fetal weight rises from first to second pregnancy.
 Smoking: Smoking in pregnancy reduces the mean birth weight by 200-400g.

PHASES OF FETAL DEVELOPMENT
 Ovular period or germinal period
 Embryonic period
 Fetal period

3. Page 3 of 33

fe
FETAL DEVELOPMENT SHARMA
 Ovular or germinal period: Lasts from the first two weeks following ovulation -when it
is designated as an ovum.
 Embryonic period: Begins at the third week following ovulation and extends upto 10
weeks of gestation (3-10wks). This is the period of cell division and differentiation.
 Fetal period: Lasts from the 10th week after the onset of the Last menstrual period
(gestation) until term.

Calendar of fetal development Change by weeks of gestational age Duration divided into:
 FIRST TRIMESTER (1-3 months)
 SECOND TRIMESTER (4-6 months)
 THIRD TRIMESTER (7-9 months)
Fertilization
 Fertilization is also known as conception, is the fusion of the sperm cell with secondary
oocyte to form the zygote.
 This process takes approximately 24 hrs and normally occurs in the ampulla of uterine
tube.

4. Page 4 of 33

fe
FETAL DEVELOPMENT SHARMA
 The acrosomal layer of the sperm secrete the enzyme hyaluronidase which disperse the
corona radiata (outermost layer of oocyte) allowing assess to zona pellucid.
 The sperm reaches to the zona pellucida and penetrates it. Upon penetration a chemical
reaction known as the cortical reaction, this alters the zona pellucida making it
impermiable to other sperm.
 The plasma membranes of the sperm and oocyte fuse, each pronucleus containing 23
chromosomes referred as haploid, and become diploid having 46 numbers of
chromosomes. This new cell is called zygote.
 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 later the secretory
cells of uterus.
 The zygote undergoes mitotic cellular replication refered as cleavage, resulting into the
formation of smaller cells known as blastomeres.
 The zygote divides into two cells- at 1st day
4 cells -at 2 days
8 by - 2.5 days
16 cells by- 3 days, Known as morula.
 The cells binds together tightly in a process known as compaction.
 Cavitation occur whereby the outermost cells secrete fluid into the morula and form
blastula comprising of 58 cells.

5. Page 5 of 33

fe
FETAL DEVELOPMENT SHARMA

Nidation:
 Implantation occurs in the endometrium of the anterior or posterior wall of the body
near the fundus on 6th day.
 Blastocyst: Possesses an inner cell mass or embryoblast and outer cell mass or
trophoblast.
 Trophoblast- becomes the placenta and chorion.
 Embryoblast- become embryo, amnion and umbilical cord.

6. Page 6 of 33

fe
FETAL DEVELOPMENT SHARMA
Embryoblast:
Develops the embryo, and differentiate into two types of cells

 Epiblast: Epiblast has three layers, which forms the particular parts of the embryo.
The first appearance of these layers, collectively known as the primitive streak is
around 15 days.
 Hypoblast: The hypoblast cells migrate along with inner cytotrophoblastic lining
secreting extracellular tissue which becomes the yolk sac.

Changes or development by weeks of gestation:
Pre embryonic period:
1-2 Week:
 No development occurs since fertilization hasn't actually occurred.
Week 3 (15-21 days)
 Fertilization occurs and form zygote.
 The embryo hatches from its protein shell and perform implantation (5-6 days).

7. Page 7 of 33

fe
FETAL DEVELOPMENT SHARMA




!1








 Trophoblast cells surrounding the embryonic cells proliferate and invade deeper into
uterine lining.
 Eventually form placenta and embryonic membrane.
 Formation of yolk sac.
 Dorsal views Primitive streak develop at 13 days.








4
th

Week

8. Page 8 of 33

fe
FETAL DEVELOPMENT SHARMA



!11








 A notochord forms in the center of the embryonic disk (day 16 of fert)
 Gastrulation commences (day 16 of fert)
 A neural groove (future spinal cord) forms over the notochord with a brain bulge at one
end.
 Neuromeres appear (day 18 of fert)
 Somites, the divisions of the future vertebra form (day 20 of fert)
 Primitive heart tube is forming.
 Vasculature begins to develop in embryonic disc (day 20 of fert)






5
th

Week

9. Page 9 of 33

fe
FETAL DEVELOPMENT SHARMA



!11









 Measures about 0.51cm-0.64cm
 Heart beats faster, at about 100 beats a minute.
 Baby has grown from an oval into a C shape and features start to develop.
 Little pits to mark ears and dimples of nostrils will be observed.
 The buds or bumps, which will grow as arms begin to swell, soon followed by legs.
 Muscle and bone tissue are forming, and she's covered with a thin layer of skin.







6
th

Week

10. Page 10 of 33

fe
FETAL DEVELOPMENT SHARMA




!11








 Fetus grows 1 cm and an extension of tailbone (coccyx) that will soon disappear.
 Webbed hand and feet.
 Brain divides into 5 vessicles including the early telencephalon.
 A loop on bulging stomach growing as intestines and as umbilical cord.
 Baby’s lifeline: Umbilical cord will develop to circulate nutrients & oxygen.








7
th

Week

11. Page 11 of 33

fe
FETAL DEVELOPMENT SHARMA



!11








 Fetus measures about 1.72 cm
 Lungs begin to form.
 The brain continues to develop as branching out to form early neural pathways.
 Arms and legs have lengthened with foot and hand areas distinguishable.
 The hands and feet have digits, moving in fits.
 The gonadal ridge begins to be perceptible.
 The lymphatic system begins to develop.
 Main development of external genitalia starts.
 Head is larger than the trunk and bent over onto her chest.






8
th

Week

12. Page 12 of 33

fe
FETAL DEVELOPMENT SHARMA




!11









 Fetus measure about 2.3cm (0.9in) from head to bottom (crown to rump) and weighs nearly
2g (0.07oz).
 Fetal fingers are slightly distinct.
 Heart has finished dividing into four chambers and senses of smell are developing.
 Organs, muscles, and nerves are all kicking into gear.
 Arms can bend at the elbows and are long enough for hands to rest on chest.







9
th

Week

13. Page 13 of 33

fe
FETAL DEVELOPMENT SHARMA




!11









 Fetus measure about 3.1cm (1.2in) from head to bottom (crown to rump) and weighs nearly
4g (0.1oz).
 Eyelids are fused shut, and will stay that way until about 27 weeks of pregnancy.
 Fingers and toes are no longer webbed.
 Stomach produces digestive juices and the kidneys are making larger quantities of urine.
 Heart beating 180 beats per minute.
 Yolk sac is no longer, it begins to disappear.
 Teeny tooth buds are now developing under the gums.





10
th

Week

14. Page 14 of 33

fe
FETAL DEVELOPMENT SHARMA




!11









 Fetus measure about 4.1cm (1.6in) from head to bottom (crown to rump) and weighs about
7gms.
 Blood vessels are visible through skin.
 Palate is fusing and milk teeth are bedding into their sockets.
 Fingers may even be growing tiny nails already.









11
th

Week

15. Page 15 of 33

fe
FETAL DEVELOPMENT SHARMA




!11









 Fetus measure about 5.4cm (2.1 in) crown to rump, weighs about 14g (5 oz).
 Fetus eyes have moved closer together.
 A fetus earlobe takes shape.
 Fetus can close & open fists.
 Fetus bone marrow producing white blood cells, able to fight against microorganism.
 Fetus pituitary gland at the base of the brain has begun producing hormones.






12
th

Week

16. Page 16 of 33

fe
FETAL DEVELOPMENT SHARMA



!11








13
th
Week:
 Fetus measure about 7.4cm (2.9 in) crown to rump, weighs about 23g (0.8 oz).
 Unique set of fingerprint start forming.
 Sex prediction.
 Formation of Vocal Cord.

14
th
Week:
 Fetus measure about 8.7 cm (3.4 in) crown to rump, weighs about 43g (1.5 oz).
 Fetus constantly changing expression from one another.
 Soft and downy hair grows all over the body.





13
th

Week
14
th

Week

17. Page 17 of 33

fe
FETAL DEVELOPMENT SHARMA




!11









 Fetus measure about 10.1cm (4 in) crown to rump, weighs about 70g (2.5 oz).
 Skeleton becoming hard and muscle tissue continues to develop.
 Fetus swallows amniotic fluid.
 Breathing and digestive systems are becoming more advanced
 Lower extremities grow each day.
 The liver and pancreas produce fluid secretions.
 Development of external genitalia is finished.





15
th

Week

18. Page 18 of 33

fe
FETAL DEVELOPMENT SHARMA


!11







16
th
Week:
 Fetus measure about 10.1cm (4 in) crown to rump, weighs about 70g (2.5 oz).
 Heart is pumping about 24 liters (42 pints) of blood around body every day.
 Head is sitting more erect on neck.
 Sensitive to light.
 Thumb sucking behavioural habit starts.

17
th
Week:
 Fetus measure about 13cm (5.1 in) crown to rump, weighs about 140g (4.9 oz)
 Umbilical becomes cord stronger & thicker.
 Hearing sense is developed.
 Skeleton is continuing to harden from rubbery cartilage to bone.
 Fat stores are beginning to develop under your baby's skin and maintain warmth of the
baby.



16
th

Week
17
th

Week

19. Page 19 of 33

fe
FETAL DEVELOPMENT SHARMA




!11









 Fetus measure about 14.2 cm (5.6 in) crown to rump, weighs about 190g (6.7oz)
 If female fetus, uterus and vagina and fallopian tubes are developing.
 If male fetus, penis will be distinct and growing rapidly.
 The fetus is more active with increased muscle development. “Quickening” usually
occurs between 18-21 weeks of gestation.








18
th

Week

20. Page 20 of 33

fe
FETAL DEVELOPMENT SHARMA


!11








19
th
Week:
 Fetus measure about 15.3 cm (6 in) crown to rump, weighs about 240g (8.5 oz)
 Sprouting of scalp hair.
 Specialized areas are developing for senses.
 Bronchioles are developed.

20
th
Week:
 Fetus measure about 25.6 cm (10 in) crown to rump, weighs about 300g (10.6 oz)
 A slick, fatty substance called vernix caseosa is beginning to form within the pores of your
baby's developing skin.





19
th

Week

20
th

Week

21. Page 21 of 33

fe
FETAL DEVELOPMENT SHARMA


!11








21
st
Week:
 Fetus measure about 25.6 cm (10 in) crown to rump, weighs about 300g (10.6 oz)
 Eyebrows and head hair are becoming thicker.
 Facial expressions, including mouthing, yawning, and sucking.
 Liver & spleen produces more blood cells.

22
nd
Week:
 Fetus measure about 27.8 cm (10.9 in) crown to heel, weighs about 430g (15.2 oz)
 Colour of eyes will continue to develop.
 Due to amniotic fluid swallow, sticky byproduct of digestive system called meconium, is
slowly building up in bowel.
 Grasping reflex developing.




21
st

Week
22
nd

Week

22. Page 22 of 33

fe
FETAL DEVELOPMENT SHARMA



!11









 Fetus measure about 28.9 cm (11.4 in) crown to heel, weighs about 500g (1.1 lb)
 Fetus is becoming more sensitive to sounds.
 Fetus can hear external sounds clearly & can respond to it.
 Bone marrow is making most of red blood cells.
 Skin becomes red in color, due transparent visuals of veins.
 Placenta effective in transport of waste from fetus body.








23
rd

Week

23. Page 23 of 33

fe
FETAL DEVELOPMENT SHARMA


!11







24
th
Week:
 Fetus measure about 28.9 cm (11.4 in) crown to heel, weighs about 500g (1.1 lb)
 Brain is growing rapidly, and facial muscles are showing different expressions, such as
smiling and scowling.
 Facial muscles are developing different expressions.
 Fetus increases weight by accumulating more brown adipose fat.

25
th
Week:
 Fetus measure about 34.6 cm (13.6 in) crown to heel, weighs about 660g (1.51 lb)
 Start to lay down fat soon.
 Startle reflex has been developed.
 Scalp continues to grow, hair color & texture changing slowly.





24
th

Week

25
th

Week

24. Page 24 of 33

fe
FETAL DEVELOPMENT SHARMA



!11








26
th
Week:
 Fetus measure about 35.6 cm (14 in) crown to heel, weighs about 760g (1.71 lb)
 150 joints, 33 rings of bone, and 1,000 ligaments are present.
 Branching of new airways with tiny air sacs (alveoli) at their tips known as respiratory tree.
 If male fetus, testicles are continuing to descend from pelvis towards scrotum.
 Fetal taste buds are fully developed.

27
nd
Week:
 Fetus measure about 36.6 cm (14.4 in) crown to heel, weighs about 875g (1.81 lb)
 Open eyes for the first time and rapid eye movements (REM) can be observed.
 Due to development of lungs, hiccups can be identified.




26
th

Week

27
th

Week

25. Page 25 of 33

fe
FETAL DEVELOPMENT SHARMA


!11








26
th
Week:
 Fetus measure about 35.6 cm (14 in) crown to heel, weighs about 760g (1.71 lb)
 150 joints, 33 rings of bone, and 1,000 ligaments are present.
 Branching of new airways with tiny air sacs (alveoli) at their tips known as respiratory tree.
 If male fetus, testicles are continuing to descend from pelvis towards scrotum.
 Fetal taste buds are fully developed.

27
nd
Week:
 Fetus measure about 36.6 cm (14.4 in) crown to heel, weighs about 875g (1.81 lb)
 Open eyes for the first time and rapid eye movements (REM) can be observed.
 Due to development of lungs, hiccups can be identified.





26
th

Week

27
th

Week

26. Page 26 of 33

fe
FETAL DEVELOPMENT SHARMA



!11








28
th
Week:
 Fetus measure about 37.6 cm (14.8 in) crown to heel, weighs about 1 kg (2.21 lb)
 A white, fatty substance called myelin is slowly wrapping around fetal spinal cord and the
nerves that branch out from it. This process is called myelination.
 Blinking reflex starts.

29
th
Week:
 Fetus measure about 38.6 cm (15.2 in) crown to heel, weighs about 1.2 kg (2.21 lb)
 Bones continue to harden.
 About 200mg of calcium is deposited in skeleton every day.





28
th

Week
29
th

Week

27. Page 27 of 33

fe
FETAL DEVELOPMENT SHARMA


!11








30
th
Week:
 Fetus measure about 39.9 cm (15.7 in) crown to heel, weighs about 1.3 kg (2.9 lb)
 Fetus responds to sound by turning head towards bright light.
 White, greasy, moisturizing vernix coats fetus skin from head to toe and from back to front.

31st Week:
 Fetus measure about 41.1 cm (16.2 in) crown to heel, weighs about 1.5 kg (3.31 lb)
 The amount of body fat rapidly increases.
 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 and pliable.




30
th

Week

31
st

Week

28. Page 28 of 33

fe
FETAL DEVELOPMENT SHARMA



!11








32
st
Week:
 Fetus measure about 42.4 cm (16.7 in) crown to heel, weighs about 1.7 kg (3.7 lb)
 Fetal fingernails are fully formed and have reached the tips of fingers.
 Except lungs, stomach and kidneys are well developed enough.

33
rd
Week:
 Fetus measure about 43.7 cm (17.2 in) crown to heel, weighs about 1.9 kg (4.2 lb)
 Fetal skull is soft and pliable, and the plates of bone that form it are not yet fused.
 Soft spot: The plates of bone in your baby’s skull are still fairly pliable.






32
st

Week
33
rd

Week

29. Page 29 of 33

fe
FETAL DEVELOPMENT SHARMA



!11








34
th
Week:
 Fetus measure about 45 cm (17.7 in) crown to heel, weighs about 2.1 kg (4.7 lb)
 Laying down a special type of fat, called brown fat which regulates body temperature.
 Waxy, cheesy coating of vernix, begins to thicken before shedding in the next few weeks.

35
th
Week:
 Fetus measure about 47.4 cm (18.7 in) crown to heel, weighs about 2.6 kg (5.7 lb)
 Fetal increases 30g per day.
 Fetal positioned head towards the cervix.






34
th

Week
35
th

Week

30. Page 30 of 33

fe
FETAL DEVELOPMENT SHARMA


!11








36
th
Week:
 Fetus measure about 47.4 cm (18.7 in) crown to heel, weighs about 2.6 kg (5.7 lb)
 Brain and nervous system are maturing fast.
 Fetal downy lanugo hair and vernix caseosa sheds off.
 Fetal move lower into pelvis is called “lightening” or “dropping.”

37
th
Week:
 Fetus measure about 48.6 cm (19.1 in) crown to heel, weighs about 2.9 kg (6.3 lb)
 Firm grasp with her hands.
 Facial muscles by practicing pouts, frowns and grimaces.
 Blinking and startle reflexes are more honed.





36
th

Week
37
th

Week

31. Page 31 of 33

fe
FETAL DEVELOPMENT SHARMA


!11








38
th
Week:
 Fetus measure about 47.4 cm (18.7 in) crown to heel, weighs about 2.6 kg (5.7 lb)
 Firm grasp with hands.

39
th
Week:
 Fetus measure about 48.6 cm (19.1 in) crown to heel, weighs about 2.9 kg (6.3 lb)
 Skin is becoming thicker and paler as new skin replaces the outer skin cells that are
sloughing off.
 Lungs are producing more surfactant and matured fully.
 Brain develops 30% more.
 Pink colored skin changes into white color.





38
th

Week
39
th

Week

32. Page 32 of 33

fe
FETAL DEVELOPMENT SHARMA




!11








40
th
Week:
 Fetus measure about 51.2 cm (20.2 in) crown to heel, weighs about 3.5 kg (7.6 lb).
 Two soft spots (fontanelles) at the top of head.
 Shed most of the vernix, the waxy coating that acted as a moisturizer, skin may be getting
dry in spots.
 Fetus ready to pass through the birth canal.








40
th

Week

33. Page 33 of 33

fe
FETAL DEVELOPMENT SHARMA
REFERENCES:
 https://www.babycentre.co.uk/pregnancy-week-by-week
 https://www.whattoexpect.com/pregnancy/week-by-week/week-4.aspx
 https://www.slideshare.net/nidhishukla77736/fetal-development-42841132
 https://www.slideshare.net/KHUSHBUPATEL135/fetal-development-and-fetal-
circulation