Fetal Development Until Birth PDF

FETAL DEVELOPMENT Lecturer, CEREN ERDEM ALTUN 15.02.2024 ISTANBUL OKAN UNIVERSITY, DEPARTMENT OF HISTOLOGY&EMBRYOLOGY FETAL PERIOD: The period from the 9th week until birth In this period; - body grows quickly → body development is very fast - tissues, organs and systems differentiate - Fetal weight...

FETAL DEVELOPMENT Lecturer, CEREN ERDEM ALTUN 15.02.2024 ISTANBUL OKAN UNIVERSITY, DEPARTMENT OF HISTOLOGY&EMBRYOLOGY FETAL PERIOD: The period from the 9th week until birth In this period; - body grows quickly → body development is very fast - tissues, organs and systems differentiate - Fetal weight gain accelerates in the last weeks GROWTH AND AGE CALCULATION Height and age of the fetus during the fetal period; - Crown rump length (CRL) - crown-to-heel (CHL) are measured by values. AC: amniotic cavity CC: chorionic cavity PREGNANCY TRIMESTERS Clinically, the pregnancy period is divided into 3 trimesters of 3 months each. all major organ systems are developed the size of the fetus develops sufficiently so that anatomical details can be seen during ultrasonography → fetal anomalies can be detected If the fetus is born prematurely (immature) at the beginning of the 3rd trimester, it may survive. The greatest development in the fetus occurs in the 35th week, - weight is ~2500g → It is a measure of fetal maturation. GROWTH AND AGE CALCULATION Crown rump length measurement (CRL) is the preferred method for fetal age determination until the end of the 1st trimester. - because very small changes occur in the fetal body during this period. FETUS DEVELOPMENT BY WEEKS While the growth of the fetus in length is more evident in the 3rd - 5th months, the increase in its weight is more evident in the last 2 months. SHAPING OF THE FETUS ❖ By the end of the 1st trimester, the fetus's face becomes more humanlike. ❖ The limbs also lengthen; but the legs are shorter and less developed than the arms. ❖ Eyes begin to develop on the side of the face and move forward. ❖ Ears take their final place. SOME IMPORTANT PROCESSES taste buds : 7th week swallowing : 10th week respiratory movements : 14th-16th weeks sucking movements : week 24 Hearing : 24th-26th week Vision (sensitivity to light): 28th week BETWEEN WEEKS 9 AND 12 ✓ At the beginning of the 9th week; The head is half the length of the CRL of the fetus. ✓ Thereafter, trunk length growth increases rapidly and by the end of the 12th week, it is more than twice the CRL. Week 11 Week 9 BETWEEN WEEKS 9 AND 12 9th week 12th week The face is wide, the eyes are wide apart, the Primary ossification centers of the skeleton, ears are lower than normal, and the eyelids especially the skull and long bones, appear. are not opened. The legs are short and relatively small. The upper extremities gain their relative final length, but the lower extremities are shorter than their final size Male and female external genitalia look similar Does not reach mature fetal shapes until the end of the 12th week The liver undertakes most of the hematopoiesis At the end of the 12th week, the spleen takes over the function of the fetal liver. Urine production begins between the 9th and 12th weeks. The fetus excretes urine into the amniotic fluid, which reabsorbs some of it after drinking it. Fetal waste materials are transferred across the placental membranes into the maternal bloodstream. BETWEEN WEEKS 13 AND 16 Development is very rapid during this period.. At the 16th week, the fetal head is relatively small compared to the 12th week, and the lower extremities are elongated. Leg movements first begin at the end of the embryonic period→ It becomes coordinated in the 14th week, but is felt very weak by the mother. → These movements are seen during ultrasound. Fetal skeletal ossification is active → At the beginning of the 16th week, bones are easily observed on ultrasound. BETWEEN WEEKS 13 AND 16 Slow eye movements are observed in the 14th week. In the 16th week, the ovary, consisting of primordial follicles containing oogoniums, differentiates. External genital organs recognizable At the 16th week, the external appearance of the fetus becomes more human-like (ears and eyes settle in their normal places). Week 13 BETWEEN WEEKS 17 AND 20 Development slows but the fetus is still growing and the CRL is approximately 50 mm. Accelerated fetal movements are felt by the mother. BETWEEN WEEKS 17 AND 20 The skin is covered with a fatty cheese-like substance called VERNIX CASEOSA. It consists of a mixture of fat secreted from the sebaceous glands and dead epithelial cells. It protects the fetal skin from abrasion, cracking and damage that can be caused by amniotic fluid. BETWEEN WEEKS 17 AND 20 Eyebrows and hair appear in the 20th week → The whole body is covered with thin hairs called LANUGO. - These hairs help the vernix caseosa to adhere to the skin. Brown fat forms during this period. - It is the energy store of the newborn. - This special fat tissue produces energy by oxidation of fatty acids. - brown adipose tissue mainly; It is located at the base of the neck, behind the sternum and around the kidney. In the 18th week, the uterus forms in the female fetus and the vagina begins to drain. Many primordial follicles are formed in the ovary. In the male fetus, at the 20th week, the testicles begin to descend towards the scrotum from hanging on the posterior abdominal wall. BETWEEN WEEKS 21 AND 25 There is a significant weight gain in the fetus and the head-to-body ratio becomes more realistic Fetal skin is more wrinkled and transparent. - In fresh specimens, the skin color ranges from pink to red. → Blood may be observed within the capillaries. Rapid eye movements begin at week 21. - It has been reported that the fetus responds to vibroacoustic sounds originating from the womb by blinking in the 22nd and 23rd weeks. Nails form in the 24th week. BETWEEN WEEKS 21 AND 25 Type II pneumocyte cells (secretory epithelial cells) in the alveolar wall of the lung begin to secrete surfactant, which ensures the effectiveness of the developing alveoli. 22.-25. When a week-old fetus is born prematurely, it can survive if it is taken to intensive care.However, it can also result in death because the fetus's respiratory system is not yet mature. Babies born before the 26th week of gestation have a high risk of neuronal developmental delay. BETWEEN WEEKS 26 AND 29 The fetus's lungs have the ability to breathe during this period → If birth occurs, it can survive with care. - lung and pulmonary vessels are sufficiently developed for gas exchange. The central nervous system is mature enough to regulate rhythmic respiratory movements and body temperature. Most deaths in newborns occur due to low (≤ 2500 g) and very low (≤ 1500 g) birth weight. BETWEEN WEEKS 26 AND 29 Eyes open at 26 weeks. Hair and lanugo are well developed. Some amount of subcutaneous fat tissue has formed, which corrects skin wrinkles. During this period, the amount of white fat reaches approximately 3.5% of body weight. Towards the end of the 28th week, the spleen's role in hematopoiesis ends → bone marrow takes over. BETWEEN WEEKS 30 AND 34 The pupillary light reflex in the eye (the change in diameter of the pupil as a response to light) can be determined at the 30th week. At the end of this period, the skin is generally pink and smooth. The amount of white fat is approximately 8% of body weight. Fetuses 32 weeks and older generally survive as a result of premature birth. BETWEEN WEEKS 35 AND 38 A normal fetus at birth weighs 3000-4000 g, CRL is 36 cm, CHL is 50 cm. The gender characteristics of the fetus are evident and the testicles have descended into the scrotum. In the last two months, subcutaneous fat tissue begins to accumulate, thus body lines become rounder. EXPECTED DATE OF BIRTH ❑266 days or 38 weeks after fertilization. ❑In other words, it is 280 days or 40 weeks after the 1st day of the last menstrual cycle. ❑However, 12% of babies are born 1 or 2 weeks after the expected due date. Immature baby: Those born before the 27th week Premature baby : Those born between 29-32 weeks Borderline premature Those born at 33-36 weeks Mature : Those born between 38-42 weeks Postmature : Those born after the 42nd week FACTORS AFFECTING FETAL GROWTH ❖Maternal, fetal and environmental factors can affect prenatal growth. ❖Factors that continue throughout pregnancy, such as maternal vascular disease, intrauterine infection, smoking, alcohol consumption → It leads to babies with intrauterine growth restriction (IUGR) or small for gestational age (SGA) babies. ❖Factors acting during the last trimester, such as maternal malnutrition, often result in babies with low birth weight despite having normal length and head growth. ❖Babies whose birth weight is 10% or less compared to gestational age are called low birth weight babies (SGA-IUGR). FACTORS AFFECTING FETAL GROWTH ❖IUGR; It refers to a process that causes a decrease in fetal growth and potential as expected. ❖SGA; It refers to a baby whose birth weight is lower than the predetermined value for a certain gestational age. The most important factor that ensures prenatal development is insulin-like growth factor 1 (IGF 1). IGF 1 is secreted by fetal tissues. Growth after the baby is born is regulated by growth hormone (GH). After GH binds to the receptor, it initiates IGF1 secretion. Laron dwarfism is observed as a result of mutations in the GH receptor. There is no IUGR in these babies. ASSESSMENT METHODS OF FETAL CONDITION It is possible to follow the development and growth of the fetus in the uterus with some methods. One of these is ultrasonography. → With this method, malformations such as the position of the placenta and fetus, multiple pregnancies, neural tube, heart and anterior abdominal wall defects can be detected. ASSESSMENT METHODS OF FETAL CONDITION Another technique used is amniocentesis. → The best time for amniocentesis is 16-18 weeks of pregnancy, counting from the last menstrual date. → In this technique, which allows the removal of some amniotic fluid, a special needle is entered into the amniotic cavity through the mother's abdominal and uterine walls and 20-30 ml of amniotic fluid is withdrawn. ASSESSMENT METHODS OF FETAL CONDITION Amniotic fluid is looked for α-fetoprotein (AFP), a fetal protein. This protein increases in neural tube defects such as anencephaly and anterior abdominal wall malformations such as omphalocele. Apart from this, fetal cells in the amniotic fluid can be grown in cell culture and analyzed for chromosomal abnormalities. ASSESSMENT METHODS OF FETAL CONDITION Another technique is chorionic villus biopsy. → By examining this tissue, which contains rapidly dividing fetal cells, biochemical defects such as chromosomal and congenital metabolic diseases can be detected in a short time. → All these techniques, except ultrasound, are used only in high-risk pregnancies. ASSESSMENT METHODS OF FETAL CONDITION These tests; → older maternal age (35 and over) → Previous family history of neural tube defects → There is another child in the family with abnormalities such as Down syndrome → Having a chromosomal anomaly in one of the parents → the mother is a carrier for one of the X-linked recessive diseases it is done in such cases.