[EMBRYO]LEC_005_THIRD-MONTH-TO-BIRTH_FETUS-AND-PLACENTA.pdf

(005) 3RD MONTH TO BIRTH: FETUS AND PLACENTA DR. PEREDO | 10/29/2020 OUTLINE Beginning of the third month: the head constitutes...

(005) 3RD MONTH TO BIRTH: FETUS AND PLACENTA DR. PEREDO | 10/29/2020 OUTLINE Beginning of the third month: the head constitutes approximately half of the CRL. I. DEVELOPMENT OF FETUS Beginning of the fifth month: the size of the head is about A. CROWN-CRUMP LENGTH one third of the CHL, and at birth, it is approximately one B. CROWN-HEEL LENGTH quarter of the CHL. Hence, over time, growth of the body accelerates but II. MONTHLY CHANGES that of the head slows down III. TIME OF BIRTH IV. PLACENTA A. FULL TERM PLACENTA B. FUNCTION OF PLACENTA C. PLACENTAL BARRIER V. UMBILICAL CORD VI. AMNIOTIC FLUID VII. PARTURITION (BIRTH) A. 3 STAGES OF LABOR I. DEVELOPMENT OF FETUS Fetal period, 9th week (3rd month) to birth Maturation of tissues and organs and rapid growth of the body Length of fetus, crown-crump length (CRL) or crown-heel length (CHL), expressed in centimeters, correlated with the age of fetus in weeks. A. CROWN-CRUMP LENGTH (CRL) sitting height from vertex of skull to the heel up to 36 cm (for a full term baby) at 37- 38 week B. CROWN- HEEL LENGTH (CHL) standing height from vertex of skull to heel up to 51 cm Figure: A 9-week fetus. Note the large head size compared with that of the rest of the body. The yolk sac and long vitelline duct are visible in the chorionic cavity. Note the umbilical cord and herniation of intestinal loops. One side of the chorion has many villi (chorion frondosum), while the other side is almost smooth (chorion laeve). Growth in length is particularly striking during: 3rd, 4th, and 5th months. An increase in weight is most striking during the last 2 months of gestation. 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. Age is calculated from the time of fertilization and is expressed in weeks or calendar months. PREPARED AND EDITED BY: KANAN S., KOLIPAKA E., PRINCE J., KUMAR R., MONCADA R., MOTIC G., MUNAR C.,  (005) 3RD MONTH TO BIRTH: FETUS AND PLACENTA DR. PEREDO | 10/29/2020 Sexual characteristics are pronounced, and the testes II. MONTHLY CHANGES should be in the scrotum 3rd month to birth, the progress or the development of the fetus is accounted month by month 3rd month – primary ossification centers, external genitalia - the testicles inside the scrotum is visible via the ultrasound in the fetus. o Fetus during 3rd month has the look of a human being (with the face, the eyes etc) but the skin is very thin that the blood vessels inside are noticeable from outside. o the face becomes more human looking. The limbs reach their relative length. external genitalia develop to such a degree that the sex of the fetus can be determined by external examination Size of the head in relation to the rest of the body at (ultrasound). At the sixth week, intestinal loops various stages of development. cause a large swelling (herniation) in the umbilical cord. 4th, 5th month – lanugo hair, fetal movement felt by mother. o If a mother goes to the doctor for a prenatal check- up, and they’re not sure when the last menstrual period was, then the month of pregnancy can be determined by whether or not they can feel the fetal movement. o The fetus is covered with fine hair, called lanugo hair; eyebrows and head hair are also visible. 6th month-respiratory system and central nervous system not yet well established, have differentiated fully, great difficulty in surviving. o The skin of the fetus is reddish and has a wrinkled appearance (because of the lack of underlying connective tissue). 7th month – developmental events occur, 90% chance of survival, the respiratory system, the sucking and the swallowing mechanisms are already developed which is why the survival is better than the 6th month. 8th month- vermix caseosa, whitish fatty substance. When a baby is delivered with whitish material covering the body, the baby has crossed the 8 month mark. 9th month- skull largest circumference of all parts of the body. If the baby is born in breech position (feet first), the circumference of the head should be known to confirm whether or not the mother will be able to deliver the head. At 18th week, the fetus has subcutaneous tissue and the attachment to placenta At the time of birth, the full term baby is 38 weeks after fertilization of 266 days (38x7) or 40 weeks. This is computed from the last normal menstrual period. Ovulation happens for 24hours but the sperm travels for 6 days. Not all eggs are fertilized right after ovulation within 24 hours. Window period is of about 6 days, and implantation is for 6- 7 days, so there’s an allowance of 10-14 days. During the last 2 months, the fetus obtains well-rounded An 18- week fetus connected to the placenta by its contours as the result of deposition of subcutaneous fat. umbilical cord. The skin of the fetus is thin because of At the time of birth, the weight of a normal fetus is 3,000 to lack of subcutaneous fat. Note the placenta with its 3,400 g, its CRL is about 36 cm, and its CHL is about 50 cm. cotyledons and the amnion. PREPARED AND EDITED BY: KANAN S., KOLIPAKA E., PRINCE J., KUMAR R., MONCADA R., MOTIC G., MUNAR C.,  (005) 3RD MONTH TO BIRTH: FETUS AND PLACENTA DR. PEREDO | 10/29/2020 (Left), An 11-week fetus. The umbilical cord still shows a swelling at its base, caused by herniated intestinal loops. The skull of this Relation of fetal membranes to wall of the uterus. (A), End of fetus lacks the normal smooth contours. Fingers and toes are well the second month. Note the yolk sac in the chorionic cavity developed. (Right), A 12—week fetus in utero. Note the extremely between the amnion and chorion. At the abembryonic pole, villi thin skin and underlying blood vessels. The face has all of the have disappeared [chorion laeve]. (B) End of the third month. human characteristics, but the ears are still primitive. Movements The amnion a d chorion have fused, and the uterine cavity is begin at this time but are usually not felt by the mother obliterated by fusion of the chorion laeve and the decidua parietalis. III. TIME OF BIRTH Intrauterine Growth Restriction (IUGR): infants who do not attain optimal intrauterine growth; pathologically Age of gestation: small, at risk for poor outcomes; gestational age taken 266 days or 38 weeks after fertilization or 40 into account. weeks from the first day of the LNMP. In women Small for Gestational Age (SGA): birth weight below with regular 28-day menstrual periods, the 10th percentile for gestational age; healthy but smaller method is fairly accurate, but when cycles are in size. no poor outcomes. Gestational period is irregular, substantial miscalculations may be taken into account also. made. An additional complication occurs when the IV. PLACENTA woman has some bleeding about 14 days after fertilization as a result of erosive activity by the Facilitates nutrient and gas exchange between maternal and implanting blastocyst. Hence, the day of delivery fetal compartments is not always easy to determine. Most fetuses are As the fetus begins the 9th week of development, its demand born within 10 to 14 days of the calculated for nutritional and other factors increase, causing the major delivery date. changes in placenta. If they are born much earlier - Premature The deposition of fetal membranes is also altered as If born later – Postmature production of amniotic increases. Ultrasound- A valuable tool for assisting in this Maternal blood is delivered to the placenta by spiral arteries determination, which can provide an accurate (1 to 2 in the uterus. days) measurement of CRL during the 7th to 14th Erosion of these maternal vessels to release blood into weeks. intervillous spaces is accomplished by endovascular Measurements commonly used in the 16th to 30th invasion by cytotrophoblast cells. weeks: Fetal component of placental is derived from trophoblast and o Ultrasound (determines the age of gestation), extraembryonic mesoderm, chorionic plate CRL, BPD (biparietal diameter), head, Maternal component is derived from uterine endometrium abdominal circumference, femur length Fetal side covered by chorionic plate. Fetal side also has Average size of newborn: 2,500-4,000g: 51 cm length blood vessels covered by the amnion connecting the fetus An accurate determination of fetal size and age is and the placenta with the umbilical cord. important for managing pregnancy, especially if the Chorion frondosum, chorionic plate (lines the trophoblast) mother has a small pelvis or if the baby has a birth Decidua basalis, decidual plate defect Junctional zone, decidual septae, compartments or Low Birth Weight (LBW): weight