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 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

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