3. 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.
5. Cont.,.,
Intrauterine development:
i) Ovum/pre-embryonic period (weeks:1-2):
• Also known as ovular/germinal period.
• Embryogenesis starts with fertilization of the egg cell (ovum)
by a sperm cell (spermatozoa). Once fertilized, the ovum is
referred to as “zygote” a single diploid cell.
• The stage of ovum lasts from conception until 14th
day. This
period covers cellular replication, blastocyst formation,
umbilical development & the embryonic membranes and of the
primary germ layers.
6. Cont.,.,
ii) Embryo (weeks:3-8):
• Embryo lasts from the day 25 until approximately 8 weeks
when conception or until the embryo measures 3cm (12
inches) from crown to rump.
• In this stage development of organs, systems, rapid cell
division occurs and most vulnerable to malformation by
environmental teratogens.
• At the end of the 8th
week all organ systems & external
structures are present.
7. Cont.,.,
ii) Fetus (weeks:9-40):
• The stage of the fetus lasts from 9 weeks until the
pregnancy ends. The fetus is less vulnerable to teratogens.
• Viability refers to the capacity of the fetus to survive
outside the uterus.
• Modern technology & with latest advancements viability
is now possible with 20 weeks after conception & fetus
weight atleast 500gms.
8. DEVELOPMENT OF FETUS BY WEEKS
OF GESTATION
1ST
TRIMESTER (1-12 WEEKS):
WEEK 1-2:
• Traveling in the fallopian tube where rapid cellular
multiplication and differentiation occurs.
• The establishment of the embryonic membranes and the
germ layers (germinal period).
• Groove formed along middle of the back for the neural tube.
9. Cont.,.,
WEEK 3:
• Fertilization occur and form zygote.
• The embryo hatches from its protein shell
and perform implantation (5-6 days).
10. Cont.,.,
WEEK 4:
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.
11. Cont.,.,
WEEK 5:
• A notochord forms in the centre of the embryonic disk. (day 16 of
fertilization)
• Gastrulation commences(day 16 of fertilization.)
• A neural groove (future spinal cord)forms over the notochord with a
brain bulge at one end. Neuromeres appears (day 18 of fertilization).
• Somites, the divisions of the future vertebra, form (day 20 of
fertilization).
• Primitive heart tube is forming.
• Vasculature begins to develop in embryonic disc (day 20 of fertilization).
13. Cont.,.,
WEEK 6:
• Embryo measures 4 mm
• The heart bulge, n begins to beat in a regular rhythm.
• 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.
15. Cont.,.,
WEEK 7:
• Length is 9 mm
• Lens pits and optic cups develops
• Nasal pits form
• Brain divides into 5 vesicles including the early telencephalon.
• Leg buds form.
• The metanephros, precursor of kidney start to develop.
• Stomach differentiation begins.
17. Cont.,.,
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.
18. Cont.,.,
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.
19. Cont.,.,
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.
20. Cont.,.,
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.
21. Cont.,.,
• 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.
23. Cont.,.,
2ND
TRIMESTER (13-27 WEEKS):
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.
24. Cont.,.,
• 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.
26. Cont.,.,
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.
28. Cont.,.,
WEEK 22:
• Taste buds are starting to form on the tongue, brain &
nerve endings can process the sensation of touch.
• For boys, the testes begin to descend from the abdomen
in this week.
• For girls, the uterus & ovaries are in place – complete
with a lifetime supply of eggs.
29. Cont.,.,
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.
30. Cont.,.,
WEEK 24:
• Fully develops inner ear, which controls balnace.
• A regular sleeping & waking cycle develops.
• With intensive medical care, babies been at 24 weeks
have more than 50% chance of survival. Complications
are frequent & serious, however such as bleeding in the
brain, nervous system and impaired vision.
31. Cont.,.,
WEEK 25:
• By 25 weeks the fetus is about 200 to 240mm in
length & weighs about 495 to 910gms.
• Skin appears wrinkled & pink to red.
• REM (rapid eye movement) begins.
• Sustained weight gain occurs.
32. Cont.,.,
WEEK 26-27:
• The fetus is 250 to 275mm in length & weighs about 910 to
1500 gms.
• Pupillary membrane disappears from eyes.
• The fetus often survives if born prematurely.
• The fetus reaches a length of 38 cm (15 inches).
• The fetus weighs about 1.2 kg.
33. Cont.,.,
• 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.
38. Cont.,.,
WEEK 35:
• The fetus is about 330 to 360mm in length & weighs about 2700 to 3400
gms.
• Face & body have loose wrinkled appearance because of subcutaneous
fat deposit.
• Body is usually plump.
• Lanugo disappears.
• Nails reaches fingertip edge.
• Amniotic fluid decreases.
• Continues to pack on the pounds & store fat all over his/her body.
39. Cont.,.,
WEEK 36:
• Fetus is between 16 &19 inches long and weighs
about 6 - 61/2 pounds.
WEEK 37:
• As fat continues to accumulate, the fetal body will
slowly becomes rounder.
• The fetus is now full-term.
40. Cont.,.,
WEEK 38:
• The average fetus is 360mm in length & weighs about
3400 to 3600 gms.
• Skin is smooth.
• Chest is prominent.
• Eyes are uniformly slate coloured.
• Bones of the skull are ossified & nearly together at sutures.
• Testes are in scrotum.
41. Cont.,.,
WEEK 39:
• The placenta continues to supply antibodies that will help
in prevention of infection for the first 6 months after birth.
WEEK 40:
• Due date arrives.
• The development is continued postnatally with adaptation
to extra uterine life & child development stages.
