Fetal period
(3
rd
month to birth)
(The fetus & placenta)
• ^ fetal period extends fro 9
th
week of gestation till birth & is
characterized by rapid growth of body & maturation of organ
systems.
• Growth in length is particularly striking during 3
rd
, 4
th
, & 5
th
months (approximately 5cm per month, whereas increase in
weight is most striking during ^ last 2 months of gestation (
700 gm per month).
• ^ length of fetus is usually indicated as ^
crown-rump length
(CRL) (sitting height), & ^ crown-heel length (CHL)(standing
height).
• ^ Length of pregnancy is considered to be 280 days, or 40
weeks after onset of last menstrual period or more accurately,
266 days or 38 weeks after fertilization.
MONTHLY CHANGES:
• One of striking changes occur during fetal life is ^ relative slow
down in growth of head compared with ^ rest of ^ body.
• At ^ beginning of 3
rd
month, ^ head constitutes approximately
half of ^ CRL,& by 5
th
month, ^ head size become one third of
CHL, & at birth it is approximately one fourth of CHL.
3
rd
month
• ^ Face more human looking.
• ^ Eyes, initially directed laterally , then move to ^ ventral
aspect of ^ face.
• ^ears come to lie close to their definitive position at ^ side of
^ head.
• ^ limbs reach their relative length in comparison to ^ rest of ^
body. Although ^ lower limbs are still a little shorter& less well
developed than ^ upper extremities.
• ^
Primary ossification centers
are present in long bones &
skull by ^12
th
week.
• Also by 12
th
week ^ external genitalia develop to such a
degree to be determined by US.
• During 6
th
week, intestinal loops cause a large swelling
(herniation) in ^ umbilical cord, but by ^ 12
th
week, ^ loops
have withdrawn into abdominal cavity.
• At ^ end of 3
rd
month, muscular activity developed.
4
th
&5
th
MONTH
• ^ fetus lengthens rapidly& at ^ end of ^ 1
st
half of intrauterine
life, its CRL is approximately 15 cm, about half ^ total length of
^ newborn.
• ^ wt. increases little during this period & by ^ end of ^ 5
th
month is still less than 500 gm.
• ^ fetus is covered by fine hair, called
lanugo hair.
• Eyebrows & head hair are also visible.
• During 5
th
month, movements of fetus can be felt by ^
mother.
6
th
MONTH
• ^ Skin is reddish & has a wrinkled appearance because of ^
lack of underlying connective tissue.
• It is difficult for a fetus of 6 months live when delivered,
although several organ systems are able to function, but ^
respiratory & nervous systems have not differentiated
sufficiently, & coordination between ^ 2 systems is not yet
well-established.
7
th
MONTH
• ^ Fetus has a CRL of about 25cm & weighs approximately
1100 gm.
• If born at this time, ^infant has 90% chance of surviving.
8
th
MONTH
• During ^ last 2 months ^ fetus obtains well-rounded contours
as ^ result of deposition of subcutaneous fat.
9
th
MONTH
• By ^ end of intrauterine life, ^ skin is covered by a whitish
fatty substance (vernix caseosa) composed of secretory
products from sebaceous glands.
• At ^ end of 9
th
month, ^ skull has ^ largest circumference of all
parts of ^ body.
• At time of birth, ^ wt. of a normal fetus is 3000-3400 gm .
• Its CRL is about 36 cm, & its CHL is about50 cm.
• Sexual characteristics are pronounced , &^ testes should be in
scrotum.