Prenatal or antenatal development refers to the process of development of an embryo or fetus during pregnancy from fertilization until birth. It involves three main periods - the pre-embryonic period from fertilization to implantation, the embryonic period from implantation to 8 weeks, and the fetal period from 9 weeks until birth. During these periods, the zygote undergoes cell division and differentiation and all major body systems and structures are developed, though they continue growing and maturing throughout pregnancy.

1. Presented by-
Ms. Nidhi Shukla
M.Sc. Nursing 1st year

2. 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.

4. 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.

5. Pre embryonic period
 Also known as ovular period or germinal period.
 Embryogenesis start with the fertilization of the egg
cell (ovum) by a sperm cell (spermatozoon). Once
fertilized, the ovum is referred to as zygote, a single
diploid cell.

6. Fertilization
 Fertilization is also known as conception, is the fusion
of the sperm cell with secondary oocyte to form the
zygote.
 The process takes approximately 24 hrs and normally
occur in the ampulla of uterine tube.

8.  The acrosomal layer of the sperm secrete the enzyme
hyaluronidase which disperse the corona radiata
(outermost layer of oocyte) allowing assess to zona
pellucida.
 The sperm reaches to the zona pellucida and
penetrates it. Upon penetration a chemical reaction
known as the cortical reaction, which alters the zona
pellucida making it impermiable to other sperm.
 The plasma membranes of the sperm and oocyte fuse,
each pronucleus containing 23 chromosomes refered
as haploid, and become diploid having 46 numbers of
chromosomes. This new cell is called zygote.

9.  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.

11.  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.

12.  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.

14. Nidation
Implantation occurs in the endometrium of the anterior
or posterior wall of the body near the fundus on 6th
day.
 The 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.

15. Trophoblast
Differentiate into two layers
syncytiotrophoblast
cytotrophoblast

16. Embryoblast
Develops the embryo, and differentiate into two types of
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 15 days.
 Hypoblast- the hypoblast cell migrate along with
inner cytotrophoblastic lining secreting extracellular
tissue which becomes the yolk sac.

17. Changes or development by weeks
of gestation
1. Pre embryonic period-
Week 1-2 – no developments occurs since fertilization
hasn’t actually occurred.
Week 3- from 15-21 days, embryonic 5-7 days.
 Fertilization occur and form zygote.
 The embryo hatches from its protein shell and
perform implantation (5-6 days).

18.  Week 4th – days 22-28 from LMP
embryonic age 2 weeks-
Events-
 Trophoblast cells surrounding the embryonic cells
proliferate and invade deeper into uterine lining.
 Eventually form placenta and embryonic membrane.
 Formation of yolk sac.
 Primitive streak develop at 13 days.
 Primary stem villi appears at 13 days

19.  Week 5
Gestational age: 4 weeks
Embryonic age: Week no. 3
 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.

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

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

26. Week 8-
 The embryo measures 13 mm (1/2 inch) in length.
 Lungs begin to form.
 The brain continues to develop.
 Arms and legs have lengthened
with foot and hand areas distinguishable.
 The hands and feet have digits, but may still be
webbed.
 The gonadal ridge begins to be perceptible.
 The lymphatic system begins to develop.
 Main development of external genitalia starts.

27. Week 9-
 The embryo measures 18 mm (3/4 inch) 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 are visible.
 Spontaneous limb movements may be detected
by ultrasound.
 All essential organs have at least begun.
 The vitelline duct normally closes

28. Fetal development
 From the 10 weeks 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 to grow.

29. Week 10 -12
 Embryo measures 30–80 mm (1.2–3.2 inches) in length.
 Intestines rotate.
 Facial features continue to develop.
 The eyelids are more developed.
 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 its fingers.
 Genitals appear well differentiated.
 Red blood cells are produced in the liver

31. Week 13-16-
 The fetus reaches a length of about 15 cm (6 inches).
 A fine hair called lanugo develops on the head.
 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, sex prediction
 At week 15, main development of external genitalia is
finished
 Abdominal wall closes.

32. Abdominal wall defects

34. Week 17-21
 The fetus reaches a length of 20 cm (8 inches).
 Lanugo covers the entire body.
 Eyebrows and eyelashes appear.
 Nails appear on fingers and toes.
 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 a stethoscope.

36. Week 23-
 The fetus reaches a length of 28 cm (11.2 inches).
 The fetus weighs about 925g.
 Eyebrows and eyelashes are well formed.
 All of the eye components are developed.
 The fetus has a hand and startle reflex.
 Footprints and fingerprints continue forming.
 Alveoli (air sacs) are forming in lungs.

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

39. Week 31
 The fetus reaches a length of about 38–43 cm (15–
17 inches).
 The fetus weighs about 1.5 kg (3 lb 0 oz).
 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.
 The fetus begins storing a lot
of iron, calcium and phosphorus

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

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

43. Thank you