Transcript Fetus and Placenta I

Fetus and Placenta I
University Of Babylon
College Of Medicine
Department Of Human Anatomy And Histology
Dr. Haythem Ali Alsayigh
Clinical Surgical Anatomy
MB.Ch.B.-F.I.M.B.S.
Third to Eighth Weeks: The Embryonic
Period
The embryonic period, or period of
organogenesis, occurs from the third to the
eighth weeks of development and is the time
when each of the three germ layers,
 ectoderm,
 mesoderm, and
 endoderm,

Third to Eighth Weeks: The Embryonic
Period
gives rise to a number of specific tissues and
organs.
 By the end of the embryonic period, the main
organ systems have been established,
 rendering the major features of the
external body form recognizable by the
end of the second month.

Fetal period
1-From the beginning of the 9th week till
birth.In which all the organs grow and
maturate
 2-The length of the fetus is usually indicated
as the crown-rump length (CRL)
(sitting height) or as
 3-The crown-heel length (CHL), the
measurement from the vertex of the skull
to the heel (standing height).

Fetal period
4-These measurements, expressed in
centimeters, are correlated with the age of
the fetus in weeks or months
 5- Few birth defects may occur in this
period and among these are defects of the
CNS.

Fetal Period
6-Growth in length is particularly
striking during the third, fourth, and fifth
months,
 7-while an increase in weight is most
striking during the last 2 months of
gestation.
 8-In general, the length of pregnancy
is considered to be 280 days,

or 40 weeks after the onset of the last
normal menstrual period
 (LNMP) or more accurately, 266 days or
38 weeks after fertilization.
 For the purposes of the following discussion,
age is calculated from the time of fertilization
and is expressed in weeks or calendar months.

STAGING OF HUMAN EMBRYO
1.counting the number of somites;
2.measurement of the crown rump length;
(sitting height).
3.measurement of the crown heel length;
(standing height).
The growth in length is more clear during the 3rd,
4th, and 5th months of development.
 The increase in weight is more clear in the last two
months of development.

Q1



1. An ultrasound at 7 months' gestation shows too
much space (fluid accumulation) in the amniotic
cavity. What is this condition called, and what are
its causes?
Answer 1. An excess of amniotic fluid is called
hydramnios or polyhydramnios, and many times
(35%) the cause is unknown (idiopathic).
A high incidence (25%) is also associated with
maternal diabetes and with birth defects that
interfere with fetal swallowing, such as esophageal
atresia and anencephaly.
Q2
2. Later in her pregnancy, a woman realizes that she was
probably exposed to toluene in the workplace during
the third week of gestation but tells a fellow worker that
she is not concerned about her baby because the
placenta protects her infant from toxic factors by acting
as a barrier. Is she correct?
 Answer 2. No. She is not correct. The placenta does not
act as a complete barrier, and many compounds cross
freely, especially lipophilic substances, such as toluene
and alcohol. Furthermore, early in pregnancy, the
placenta is not completely developed, and the embryo is
particularly vulnerable. These early weeks are also very
sensitive to insult by compounds such as toluene, which
causes toluene embryopathy.

Counting the date of birth
Birth occurs 40 weeks after the onset of the
last normal menstrual period (LNMP), this
period equals 280 days.
 Also, this period is about 266 days or 38 weeks
after fertilization.
 Obstetricians calculate the expected date of
birth as +7 (days) -3 (months) from the date of
the LNMP. This method is accurate if the cycle
was of regular 28 days duration.

Counting the date of birth
Miscalculation occurs in the presence of an irregular
cycle or due to the false menstruation occurring due to
the bleeding from the lacunar blood flow ( day 13 after
fertilization).
 Birth occurring before this date is called premature
birth, while birth later than this date is called
postmature birth.
Usually fetal age is determined by combining: 1. date of 
LNMP 2. length 3. weight
4. external morphology of the fetus.

Counting the date of birth

The determination of the expected delivery date
by the ultrasound examination is much helpful.,
By US the CRL is
measured
during 7-14th
weeks
Counting the date of birth

The determination of the expected delivery date
by the ultrasound examination is much helpful.,
Also the
Biparietal
diameter of the
skull is done from
16-30th weeks
Counting the date of birth

The US measurements also done for the
circumferences of the head and the abdomen.
Counting the date of birth

and for measurement of the length of femur.
The main external features of the
embryos and fetuses
1.features at the first
month;
1.the presence of embryo
somites.
2.the pharyngeal arches.
The main external features of the
embryos and fetuses
2.features at the
second month;
1. CRL about 30mm
2. large head (with
ears and eyes on
sides). nose is seen.
3. limb bud formation.
4. large swelling of the
developing umbilical
cord
The main external features of the
embryos and fetuses
3.features at the third month;
1. Head about ½ CRL.
2. Face more human like.
3. Primary ossification centers seen in long bones and skull.
4. Fetal sex could be determined by U/S.
5. Withdrawn of intestinal loop in umbilical cord is inside
the abdominal cavity.
6.The limbs reach their relative length in comparison with
the rest of the body, although the lower limbs are still a
little shorter and less well developed than the upper
extremities
3.features at the third month;
4.features at the fifth month:
1. Head about 1/3 of CHL.
2.CRL is about 15 cm.
3. Weight is increased up to
500gm.
4. fetus covered with lanugo hair
(white hair).
5. eye brow and head hair are
visible.
6. fetal movements are clear and
easily felt by mother
The main external features of the
embryos and fetuses
5.features at the sixth month:
1.the skin is red and wrinkled with no subcutaneous
connective tissue.
2.all the organs are functioning, but there is no
coordination between the CNS and the respiratory
system. Therefore, aborted fetus is very difficult to
survive. Fetus of 7 months age able to survive also
with difficulty.
3.CRL is about 24cm.
4.the weight is about 900gm.
The main external features of the
embryos and fetuses
6.features at the last two months:
1. Fetus well rounded by deposition of subcutaneous
fat.
2.CRL about 31-34cm.
3. Weight increased markedly to about 1400-2900gm.
The main external features of the
embryos and fetuses
7.features at birth:
1. Head about ¼ of CHL. head circumference is the
largest of all body parts.
2. skin is covered by vernix caseosa secreted from
sebaceous gland.
3. Weight is about 3000-3400gm.
4. CRL is about 36cm. CHL is about 50cm.
5. sex features are clear and testes lie in the scrotum
The main external features of the
embryos and fetuses
A fetus born early in the sixth month has great difficulty
surviving.
 Although several organ systems are able to function,
the respiratory system and the central nervous system
have not differentiated sufficiently,and coordination
between the two systems is not yet well established.
 By 6.5 to 7 months, the fetus has a length of about 25
cm and weighs approximately
 1100 g. If born at this time, the infant has a 90% chance
of surviving. Some developmental events occurring
during the first 7 months are indicated in

THE END
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