The document outlines the stages of fetal development from 9 weeks to birth, detailing key growth milestones, organ differentiation, and changes occurring in both the fetus and placenta. It covers various periods, emphasizing rapid growth phases, the establishment of vital functions like urine formation and nutrient exchange, and physical developments including limb formation and the differentiation of reproductive organs. Additionally, the document highlights the importance of the placenta and various physiological changes leading to childbirth.

1. Fetal DevelopmentFetal Development
From 9 weeks to birthFrom 9 weeks to birth
Prof Dr Ambreen UsmaniProf Dr Ambreen Usmani
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2. Learning objectivesLearning objectives
• Describe the events of development fromDescribe the events of development from
9 weeks to birth9 weeks to birth
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3. IntroductionIntroduction
• Development during fetal period isDevelopment during fetal period is
concerned primarily with body growth andconcerned primarily with body growth and
differentiation of tissues, organs anddifferentiation of tissues, organs and
systemssystems
• The rate of body growth is rapidThe rate of body growth is rapid
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4. Estimation of fetal ageEstimation of fetal age
• US measurement of crown-rump lengthUS measurement of crown-rump length
(CRL) can be used to determine fetal size(CRL) can be used to determine fetal size
and probable ageand probable age
• It can be used to provide a reliableIt can be used to provide a reliable
prediction of the expected date of deliveryprediction of the expected date of delivery
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5. 9 weeks to 12 weeks9 weeks to 12 weeks
• Beginning– the head constitutes half of theBeginning– the head constitutes half of the
CRL of the fetusCRL of the fetus
• Face is broad, eyes are widely separated,Face is broad, eyes are widely separated,
the ears are low set and the eye-lids arethe ears are low set and the eye-lids are
fusedfused
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7. Limbs (9-12 weeks)Limbs (9-12 weeks)
• Upper limbs have almost reached theirUpper limbs have almost reached their
final relative lengthsfinal relative lengths
• Lower limbs are relatively smaller thanLower limbs are relatively smaller than
their final lengthstheir final lengths
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8. ErythropoiesisErythropoiesis
• Liver is a major site for erythropoiesisLiver is a major site for erythropoiesis
initiallyinitially
• By the end of 12 weeks- activity hasBy the end of 12 weeks- activity has
decreased in the liver and has begun indecreased in the liver and has begun in
the spleenthe spleen
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9. Urine formationUrine formation
• Begins between the 9Begins between the 9thth
and 12and 12thth
weeksweeks
• Urine is discharged through the urethraUrine is discharged through the urethra
into the amniotic fluidinto the amniotic fluid
• Fetus reabsorbs some of this fluid afterFetus reabsorbs some of this fluid after
swallowing itswallowing it
• Waste products are transferred to theWaste products are transferred to the
maternal circulation by passing across thematernal circulation by passing across the
placental membraneplacental membrane
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10. 13 weeks to 16 weeks13 weeks to 16 weeks
• Growth is rapidGrowth is rapid
• Head is relatively smallHead is relatively small
• Limb movementsLimb movements
• Ossification of fetal skeletal is activeOssification of fetal skeletal is active
• Eyes- slow eye movementsEyes- slow eye movements
• HairHair
• Ovaries are differentiatedOvaries are differentiated
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11. 17 weeks to 20 weeks17 weeks to 20 weeks
• Growth slowsGrowth slows
• QuickeningQuickening
• Vernix caseosaVernix caseosa
• Eye brows and head hair are also visible at 20Eye brows and head hair are also visible at 20thth
weeksweeks
• LanugoLanugo
• Brown fat formsBrown fat forms
• Uterus is formed and canalization of vagina has beganUterus is formed and canalization of vagina has began
(18weeks)(18weeks)
• Primordial ovarian follicles containing oogoniaPrimordial ovarian follicles containing oogonia
• testestestes
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12. PlacentaPlacenta
• The placenta is the primary site of nutrient andThe placenta is the primary site of nutrient and
gas exchange between mother and fetusgas exchange between mother and fetus
• The placenta is a fetomaternal organ that has 2The placenta is a fetomaternal organ that has 2
components by the beginning of 4components by the beginning of 4thth
monthmonth
#fetal part#fetal part
#maternal part#maternal part
• The uterus ,chorionic sac and placenta enlargesThe uterus ,chorionic sac and placenta enlarges
as the embryo and later the fetus growsas the embryo and later the fetus grows
(18weeks old). During these weeks the placenta(18weeks old). During these weeks the placenta
weighs about 1/6weighs about 1/6thth
that of fetusthat of fetus
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13. 1313

14. 1414

15. 21 to 25 weeks21 to 25 weeks
• Weight gainWeight gain
• SkinSkin
• Rapid eye movement (at 21 weeks)Rapid eye movement (at 21 weeks)
• Blink-startle response (22-23 weeks)Blink-startle response (22-23 weeks)
• Surfactant (24 weeks)Surfactant (24 weeks)
• Finger nails (24 weeks)Finger nails (24 weeks)
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16. 1616

17. 1717

18. 26 weeks to 29 weeks26 weeks to 29 weeks
• Lungs and pulmonary vasculature haveLungs and pulmonary vasculature have
developed sufficientlydeveloped sufficiently
• CNS has maturedCNS has matured
• Eye lids are open at 26 weeksEye lids are open at 26 weeks
• Lanugo and head hair are well developedLanugo and head hair are well developed
• Toe nailsToe nails
• SkinSkin
• The fetal spleen is now an important site ofThe fetal spleen is now an important site of
hematopoiesis.Erythropoiesis in the spleen ends by 28hematopoiesis.Erythropoiesis in the spleen ends by 28
weeks ,then the bone marrow becomes the major site ofweeks ,then the bone marrow becomes the major site of
this processthis process
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19. 1919

20. 30 to 34 weeks30 to 34 weeks
• Pupillary light reflex can be elicitedPupillary light reflex can be elicited
• The skin is pink and smooth .The upperThe skin is pink and smooth .The upper
and lower limbs have a chubbyand lower limbs have a chubby
appearanceappearance
• The quantity of white fat is about 8% ofThe quantity of white fat is about 8% of
body weightbody weight
• Fetuses 32 weeks and older usuallyFetuses 32 weeks and older usually
survive if born prematurelysurvive if born prematurely
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21. 2121

22. 35 to 38 weeks35 to 38 weeks
• Nervous system is sufficiently matureNervous system is sufficiently mature
• Most fetuses during this finishing periodMost fetuses during this finishing period
are plumpare plump
• By 36 weeks circumferences of the headBy 36 weeks circumferences of the head
and abdomen are approximately equaland abdomen are approximately equal
after this ,the circumference of theafter this ,the circumference of the
abdomen maybe greater than the headabdomen maybe greater than the head
• Fetal foot measurement is usually slightlyFetal foot measurement is usually slightly
larger than femoral length at 37 weekslarger than femoral length at 37 weeks
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23. 2323

24. Full termFull term
• Most fetuses have a CRL of 360mm andMost fetuses have a CRL of 360mm and
weight about 3400gmweight about 3400gm
• White fat is about 16% of body weightWhite fat is about 16% of body weight
• A fetus adds about 14gms of fat a dayA fetus adds about 14gms of fat a day
during these last weeks of gestationduring these last weeks of gestation
• Testes are in scrotum usuallyTestes are in scrotum usually
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25. Parturition (child birth)Parturition (child birth)
Fetus ,placenta and fetal membranes areFetus ,placenta and fetal membranes are
expelled from the mother’s reproductiveexpelled from the mother’s reproductive
tracttract
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26. 2626

27. 2727

28. 2828

29. 2929

30. 3030

31. PlacentaPlacenta
• The placenta is the primary site of nutrient andThe placenta is the primary site of nutrient and
gas exchange between mother and fetusgas exchange between mother and fetus
• The placenta is a fetomaternal organ that has 2The placenta is a fetomaternal organ that has 2
components by the beginning of 4components by the beginning of 4thth
monthmonth
#fetal part#fetal part
#maternal part#maternal part
• The uterus ,chorionic sac and placenta enlargesThe uterus ,chorionic sac and placenta enlarges
as the embryo and later the fetus growsas the embryo and later the fetus grows
(18weeks old). During these weeks the placenta(18weeks old). During these weeks the placenta
weighs about 1/6weighs about 1/6thth
that of fetusthat of fetus
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32. • Fetal part of the placenta is formed byFetal part of the placenta is formed by
villous chorionvillous chorion
• Maternal part is formed by decidua basalisMaternal part is formed by decidua basalis
• By the end of 4By the end of 4thth
month decidua basalis ismonth decidua basalis is
replaced by the fetal partreplaced by the fetal part
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33. Fetomaternal junctionFetomaternal junction
• Cytotrophoblastic shell—the external layer ofCytotrophoblastic shell—the external layer of
trophoblastic cells on the maternal surface of thetrophoblastic cells on the maternal surface of the
placentaplacenta
• The decidua capsularis ,is the layer of deciduaThe decidua capsularis ,is the layer of decidua
overlying the implanted chorionic sac ,forms aoverlying the implanted chorionic sac ,forms a
capsule over the external surface of the saccapsule over the external surface of the sac ,as,as
the conceptus enlarges ,the dc bulges into thethe conceptus enlarges ,the dc bulges into the
uterine cavity and becomes greatly attenuated.uterine cavity and becomes greatly attenuated.
By 22-24 weeks ,the reduced blood supply to theBy 22-24 weeks ,the reduced blood supply to the
dc causes it to degenerate and disappeardc causes it to degenerate and disappear
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34. Amniochorionic membraneAmniochorionic membrane
• The amniotic sac enlarges faster than theThe amniotic sac enlarges faster than the
chorionic sac as a result ,the amnion andchorionic sac as a result ,the amnion and
smooth chorion soon fuse to form thesmooth chorion soon fuse to form the
amniochorionic membraneamniochorionic membrane
• It is the amniochorionic membrane thatIt is the amniochorionic membrane that
ruptures during laborruptures during labor
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35. Placental circulationPlacental circulation
• Fetal placental circulationFetal placental circulation
• Maternal placental circulationMaternal placental circulation
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36. 3636

37. Placental membranePlacental membrane
• Structure that consists of the extrafetal tissuesStructure that consists of the extrafetal tissues
separating the maternal and fetal bloodseparating the maternal and fetal blood
• At 20At 20thth
week ,the placental membrane consistsweek ,the placental membrane consists
of 4 layersof 4 layers
syncytiotrophoblassyncytiotrophoblas
connective tissue of villusconnective tissue of villus
cytotrophoblastscytotrophoblasts
endothelium of fetal capillariesendothelium of fetal capillaries
• After 20After 20thth
week ,histological changes occurweek ,histological changes occur
• As pregnancy advances ,the placentalAs pregnancy advances ,the placental
membrane becomes progressively thinnermembrane becomes progressively thinner
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