2. Introduction
Pregnancy is measured in trimesters from the
first day of last menstural period, totaling 40
weeks
The first trimester starts from week 1 through
week12, or about 3 months
The second trimester is week 13 to week 27 &
The third trimester of pregnancy spans from
week 28 to till the birth
3.
4. Germ cells(Oogonia) are diploid
Mitosis occurs - Maximum germ cells @ 20 wk
is 7 million
Meiosis-I occurs in primary oocyte(46 XX)
Meiosis-I gets arrested @ birth(2 million) in
late prophase
Ovaries are silent till puberty
Meiosis-I resumes @ puberty(4 lakhs)
Meiosis-I is completed @ ovulation(3 hrs
before ovulation)
End product is secondary oocyte(23X) & first
polar body
Meiosis-II occurs but it gets arrested in
Metaphase
Meiosis-II gets completed @ fertilization and
leads to formation of Mature ovum(23X) &
second polar body
5. Fertilization is fusion of sperm and mature
ovum and leads to the producion of zygote
It takes place in ampulla of fallopian tube
1st cleavage phase of zygote is 30hrs
Zygote divides and forms 16 cell stage
known as morulla
Morulla enters uterine cavity by 4-5th day
after fertilization
Now it further divided and fluid gets
accumulated to form Blastula which is the
implantation stage
6. Blastula is also called Blastocyst
Implantation site - Posterior wall of uterus near
fundus
Day of implantation - 6th day and it gets over by 10th
day
Blastocyst has an 1. Outer cell layer - Trophoblast
2. Inner cell mass - Embryoblast
Trophophoblast is the Future placenta
2 types of trophoblast - syncitiotrophoblast and
cytotrophoblast
Syncitiotrophoblast forms HCG and progesterone
7. Cytotrophoblast is the invading trophoblast
Decidua - Endometrium of pregnancy
3 types-
1.Decidua Basalis - Site of implantation
2.Decidua Capsularis - Covers zygote
3.Decidua Parietalis - Remaining portion
8. Embryoblast forms embryonic plate which divides
into Ectoderm and Endoderm
1.Ectoderm - faces amniotic cavity
It forms- Skin, Hair, Nails, Teeth, Notochord,
Neural crest, CNS, PNS & Primitive streak -
Mesoderm = vessels and connective tissue
2.Endoderm - faces yolk sac cavity
It forms- Fore gut
Mid gut and
Hind gut
10. WEEKS OF GESTATION FETAL DEVELOPMENT
1 & 2 Woman is not yet pregnant
3 Fertilization
4 Implantation
5 Embryonic period begins
6 Neural tube closes & its heart starts pumping blood
7 Embryos head develops, arm buds develop and take
on the shape of paddles
8 Eyes are visible, Arms and legs are growing longer &
fingers have begun to form
9 Arms grow, develop bones and bend at the elbows
Toes form
10 Neck begins to develop
11. WEEKS OF GESTATION FETAL DEVELOPMENT
11 Fetal genital develop
12 Fetal fingernails develop
13 Urine forms
14 Fetal sex becomes apparent
15 Fetal skeleton develops bones
16 Fetal can make sucking motions with his or her mouth
Fetal movements are becoming coordinated and can be detected
during ultrasound
17 Fat stores begin to develop under its skin
18 Ears begin to stand out on the sides and begin to hear
19 Vernix caseosa begins to cover fetus
Fetal uterus and vagina forms
12. WEEKS OF GESTATION FETAL DEVELOPMENT
20 Quickening
21 Fetus can swallow
22 Fetus completely covered with a fine, down-like hair
called lanugo. It helps to hold the vernix caseosa on
the skin
23 Fingerprints and footprints form
For boys, the testes are descending from the abdomen
For girls, uterus and ovaries are in place
24 Real hair grows
25 Fetus moves and responds to sounds
26 Fetal lungs are begin to produce surfactant
27 Fetal lungs and nervous system are continuing to
mature
13. WEEKS OF GESTATION FETAL DEVELOPMENT
28 Fetal eyes open
29 Fetal bones are fully developed
30 Fetal eyes are wide open
Red blood cells are now forming in bone marrow
31 Nervous system development continues
32 Fetus practices breathing
Lanugo starts to fall off
33 Fetus detects light
34 Fetus fingernails grow
35 Fetus's limbs are becoming chubby and gaining
weight rapidly
14. WEEKS OF GESTATION FETAL DEVELOPMENT
36 Fetus takes up most of the amniotic sac
37 Fetus will be considered early term
38 Fetus develops a firm grasp
39 Fetus chest become prominent
For boys, testes continue to descend into the
scrotum
Placenta continues to supply antibodies that willl
help fight infection after birth
40 Pregnancy due date arrives
15. Terminologies
Zygote - Collection of cells from fertilization to 2 wks
Embryo - 3 to 8 wks
Fetus - 9 wks to birth
Newborn or Neonate - Birth to 28 days
Infant - Upto 1 yr
Toddler - 1 to 3 yrs
17. Fetal circulation:
The human fetal circulation( feto placental circulation) which includes the umbical
cord and the blood vessels within the placenta that carry fetal blood circulation of
oxygenated blood,de-oxygenated blood and the nutritive materials
Placenta: Where gas exchange takes place during fetal circulation
Umbilical cord:
2 Umbilical arteries: Carry de-oxygenated blood, fecal waste, Co2 from fetus to
the placenta
1 Umbilical vein: Brings oxygenated blood and nutrients from placenta to the
fetus
18. Three shunts of fetal circualtion:
1. Ductus venosus:
Connects the umbilical vein to the inferior vena cava
It carries oxygenated blood from the umbilical vein to inferior venacava, by passing the
liver
2. Ductus arteriosus:
Connects the main pulmonary artery to the aorta
It carries the oxygenated blood from pulmonary artery to aorta, by passing the lungs
3.Foramen ovale:
Anatomic opening between the right and left atrium
It pushes blood from the right atrium to the left atrium
19. Oxygenated blood enters the umbilical vein
from the placenta
Enters ductus venous
Passes through the inferior venacava
Enters the right atrium
Enters the foramen ovale
Goes to the left atrium& Passes to the left
ventricle
Flows to the ascending aorta to supply the brain
and upper extremities
20. Enters the superior venacava
Goes to the right atrium and to the right
ventricle
Enters the pulmonary artery with some blood
going to the lungs to supply oxygen and
nourishment
Flows to ductus arteriosus
Enters the descending aorta with some blood
goes to the lower extremities
Enters the hypogastric arteries
Goes back to the placenta
