Fetal Development and Health

Fetal Period Overview

• The fetal period is a transformational time in prenatal development
• It signifies that the primordia of all major systems have formed
• Development is marked by rapid body growth and tissue, organ, and system differentiation
• A notable change is the slowdown in head growth relative to the rest of the body
• Body growth rate is rapid
• Fetal weight gain is phenomenal during the terminal weeks
• Normal continuous growth alternates with intervals of absent growth

Estimating Fetal Age

• Ultrasound measurements of the crown-rump length (CRL) determine fetal size and probable age
• CRL is used to predict the expected delivery date
• Fetal head and femur length measurements are valuable for age evaluation
• Gestational age is timed from the onset of the last normal menstrual period (LNMP) in clinical practice
• Gestational age based on the LNMP tends to be inconsequential

Viability of Fetuses

• Viability is defined as the ability of fetuses to survive in an extrauterine environment
• Fetuses weighing less than 500 g at birth do not usually survive
• Survival at gestational ages of 22 to 23 weeks has been increasingly reported
• Expert postnatal care may enable fetuses born at less than 1000 g to survive
• These infants are considered extremely low-birth-weight infants
• Many full-term, low-birth-weight infants result from intrauterine growth restriction (IUGR)
• Some fetuses weighing less than 500 g may survive with expert postnatal care
• Most fetuses weighing between 750 and 1500 g usually survive, but complications may occur
• Approximately 500,000 preterm infants (<37 weeks) are born in the US each year
• Many of these infants suffer from severe medical complications or early mortality (death)
• Antenatal steroids and postnatal administration of endotracheal surfactant have greatly lowered the rates of acute and long-term morbidity
• Prematurity is a common cause of morbidity and perinatal death

Criteria for Estimating Fertilization Age

• Includes the age, crown-rump length, foot length, fetal weight and characteristics of previable fetuses
• Features include closing eyelids, indistinct genitalia, abdomen intestines sitting outside of the abdomen and low set ears
• Features include intestines in the abdomen, fingernail development and neck
• Features include external ears, vernix caseosa and visible head and body hair
• Also includes data and features of viable fetuses with ages up to 38 weeks
• Features include pink skin, fingernails, eyelashes, open eyes, body and toenails filling out
• Finally features testes in scrotum and developed fingernails protruding beyond the finger tips
• There isn't a fixed limit of development, age, or weight at which a fetus automatically becomes viable
• Experience has shown that it is rare for a baby to survive whose weight is less than 500 g or whose fertilization age is less than 22 weeks
• Even fetuses born between 26 and 28 weeks have difficulty surviving, because of the under developed respiratory and central nervous systems

Pregnancy Trimesters

• Clinically, gestation is divided into three trimesters, each lasting 3 months
• The first trimester sees development of major systems
• The fetus grows sufficiently in size during the second trimester
• Good anatomical detail can be visualized, most major birth defects can be detected using high-resolution real-time ultrasonography
• By the third trimester, the fetus may survive if born prematurely
• The fetus reaches a major developmental landmark at 35 weeks
• At 35 weeks, the fetus weighs approximately 2500 g and usually survives if born prematurely

Measurements and Characteristics of Fetuses

• Various measurements and external characteristics are useful for estimating fetal age
• CRL is the method of choice for estimating fetal age until the end of the first trimester
• There is very little variability in fetal size during this period
• In the second and third trimesters, several structures can be identified and measured ultrasonographically
• Biparietal diameter, head circumference, abdominal circumference, femur length, and foot length are measured
• Weight is often a useful criterion for estimating age
• There may be a discrepancy between the age and weight
• This occurs particularly when the mother has had metabolic disturbances such as diabetes mellitus during pregnancy
• Fetal dimensions obtained from ultrasound measurements closely approximate CRL measurements obtained from spontaneously aborted fetuses
• Determination of the size of a fetus, especially its head circumference, is helpful to the obstetrician for management of patients

Fetal Period Highlights (Weeks 9-12)

• There is describing the changes that occur in periods of 4 to 5 weeks
• At the beginning of the fetal period, the head constitutes approximately half of the CRL of the fetus
• By the end of 12 weeks, the CRL has almost doubled
• Growth of the head slows down considerably by this time
• The head is disproportionately large compared with the rest of the body
• At 9 weeks, face is broad, the eyes are widely separated, the ears are low set, and the eyelids are fused
• By the end of 12 weeks, primary ossification centers appear in the skeleton and long bones
• By the end of 12 weeks, the upper limbs have almost reached their final lengths
• The lower limbs are still not so well developed, and they are slightly shorter than their final relative lengths
• The external genitalia of males and females appear similar until the end of the ninth week
• Mature form is not established until the 12th week
• Intestinal coils are visualized at in the proximal end of the umbilical cord until the middle of the 10th week
• By the 11th week, the intestines have returned to the abdomen
• At 9 weeks, the liver is the major site of erythropoiesis
• By the end of 12 weeks, this activity has decreased in the liver and has begun in the spleen
• Urine formation begins between the 9th and 12th weeks
• Urine is discharged through the urethra into the amniotic fluid
• The fetus reabsorbs some amniotic fluid after swallowing it
• Fetal waste products are transferred to the maternal circulation by passage across the placental membrane

Fetal Period Highlights (Weeks 13-16)

• Fetal growth is very rapid during this period
• By 16 weeks, the head is relatively smaller than the head of a 12-week fetus
• By 14 weeks limb movements become coordinated, but are too slight to be felt by the mother
• Ossification of the fetal skeleton is active during this period
• Developing bones are clearly visible on ultrasound images by the beginning of the 16th week
• Slow eye movements occur at 14 weeks
• Scalp hair patterning is also determined during this period
• By 16 weeks the ovaries are differentiated and contain primordial ovarian follicles
• Genitalia of male and female fetuses can be recognized by 12 to 14 weeks

Fetal Period Highlights (Weeks 17-20)

• Growth slows down during this period
• The fetus still increases its CRL by approximately 50 mm
• Fetal movements (quickening) are commonly felt by the mother
• The skin is now covered with a greasy, cheese-like material, called vernix caseosa
• Vernix consists of a mixture of dead epidermal cells and a fatty substance from the fetal sebaceous glands
• The vernix protects the delicate fetal skin from abrasions, chapping, and hardening that result from exposure to the amniotic fluid
• Fetuses are covered with fine, downy hair, lanugo, which helps the vernis adhere
• Eyebrows and head hair are visible at 20 weeks
• Brown fat forms during this period and is the site of heat production
• Fetal uterus is formed by 18 weeks
• Vagina canalization has begun.in females
• The testes have begun to descend (in males)
• Ovaries and testes still located on the posterior abdominal wall.

Fetal Period Highlights (Weeks 21-25)

• Substantial weight gain occurs during this period
• The fetus is better proportioned
• The skin is usually wrinkled and more translucent, particularly during the early part of this period
• The skin is pink to red because blood in the capillaries is visible
• At 21 weeks, rapid eye movements begin
• Blink-startle responses have been reported at 22 to 23 weeks
• The secretory epithelial cells (type II pneumocytes) in the interalveolar walls of the lung have begun to secrete surfactant
• Fingernails are present by 24 weeks
• There is a chance that a 22- to 25-week fetus born prematurely may die if given intensive care
• The risk for neurodevelopmental disability is high in fetuses born before 26 weeks

Fetal Period Highlights (Weeks 26-29)

• Fetuses usually survive if they are born prematurely, and are given intensive care
• The lungs and have developed sufficiently to provide adequate gas exchange
• In addition, the has matured to the stage where it can direct rhythmic breathing movements and control
• The highest rate of neonatal mortality occurs in infants classified as birth weight (≤2500 g) and very low birth weight (≤1500 g)
• The eyelids are open at 26 weeks, and and head hair are well developed
• Toenails are visible, and considerable subcutaneous fat is under the skin, smoothing out many of the wrinkles
• The quantity of increases to approximately 3.5% of the body weight
• Spleen becomes an important erythropoiesis (formation of red blood cells) ends at 28 weeks
• The bone marrow has become the major site of erythropoiesis

Fetal Period Highlights (Weeks 30-34)

• The pupillary reflex can be elicited at 30 weeks.
• Usually by the end of this period, the skin is pink and smooth and the upper and lower limbs have a chubby appearance.
• At this age, the quantity of white fat is approximately 8% of the body weight.
• Fetuses 32 weeks and older usually survive if born prematurely.

Fetal Period Highlights (Weeks 35-38)

• Fetuses born at 35 weeks have a firm grasp and exhibit a spontaneous orientation to light.
• As term approaches, the nervous system is sufficiently mature to carry out some integrative functions
• Most fetuses during this "finishing period" are plump.
• By 36 weeks, the circumferences of the head and abdomen are approximately equal.
• After this, the circumference of the abdomen may be greater than that of the head. The foot length of fetuses is usually slightly larger than the femoral length at 37 weeks and is an alternative parameter for confirmation of fetal age.
• There is a slowing of growth as the time of birth approaches.
• At full term (38 weeks), most fetuses usually reach a CRL of 360 mm and weigh approximately 3400 g.
• The amount of white fat is approximately 16% of the body weight.

Low Birth Weight

• Low-birth-weight babies are not always premature.
• Approximately one third of those with a birth weight of 2500 g or less are actually small for gestational age
• Small-for-date infants may be underweight because of placental insufficiency
• Placentas are small or poorly attached and/or have undergone degenerative changes
• It is important to distinguish between full-term neonates who have a low birth weight (IUGR) and preterm neonates
• IUGR may be caused by preeclampsia, smoking or some illicit drugs, multiple gestations, infectious diseases, cardiovascular defects, inadequate maternal nutrition, and maternal and fetal hormones.
• Teratogens and genetic factors are also known to cause IUGR
• Infants with asymmetrical forms of IUGR show a characteristic lack of subcutaneous fat
• Their skin is wrinkled, suggesting that white fat has actually been lost

Postmaturity Syndrome

• Postmaturity syndrome or the prolongation of pregnancy occurs in 5% to 6% of women
• Infants develop the postmaturity syndrome; which may be associated with fetal dysmaturity: absence of subcutaneous fat, wrinkling of the skin, or meconium staining of the skin.
• Fetuses with postmaturity syndrome faces an increased risk of mortality
• Labor is usually induced when the fetus is postmature

Expected Date of Delivery

• Expected date of delivery 266 days or 38 weeks after fertilization
• 280 days or 40 weeks after LNMP
• Approximately 12% of fetuses born 1 to 2 weeks after the expected time

Factors Influencing Fetal Growth

• Affect prenatal growth: maternal, fetal, or environmental factors.
• Substrates needed: gases (glucose), and nutrients (amino acids). -Placental membrane permeability: insulin insulin-like growth factors
• Somatomedin and growth hormone: stimulate fetal growth.
• Maternal vascular disease, infection, smoking, alcohol: IUGR or SGA.
• Maternal malnutrition: underweight infants with normal length and head size.

Cigarette Smoking

• Well-established cause of IUGR
• The growth rate of fetuses of mothers who smoke cigarettes is less than normal during the last 6 to 8 weeks of pregnancy
• Affects birth-weight by approximately less 200g, increased perinatal morbidity
• Cigarette may be the cause of cleft lip and palate.

Illicit and Multiple Substances

• Individuals of multiple births typically weigh less from a single pregnancy due to metabolic demands.
• Alcohol causes IUGR, fetal alcohol syndrome
• Marijuana and cocaine induce IUGR and other complications.

Impaired Uteroplacental Blood Flow

• Maternal placental circulation may be reduced in small vessel size and hypotension
• Placental dysfunction causes infarctions
• Genetic factors in one family linked to IUGR with genes Structural of chromosomal cause IUGR

Ultrasonography

• Primary imaging diagnoses Placental, multiple births, abnormalities shape, and in presentation
• Ultrasound scans is how they measure diameter of the fetal cranium
• Abnormal pregnancies early Ultrasound
• 3-Dimensional technique in tool in early abnormalities
• Rapid advances in technology have made it a major tool for diagnosing fetal abnormalities in early pregnancy
• Biopsy of fetal tissues, can be performed with ultrasound guidance.

Diagnostic Amniocentesis

• Common prenatal procedure in with the use of samples of the fluid after 15
• 22 gauge (g) is how amniotic fluid is retrieved
• Amniotic fluid volume is approximately 200 ml, and 15 to 20 ml can be safely withdrawn
• Procedure relatively small risk to the fetus (a pregnancy loss of 0.5% to 1.0%), especially when the procedure is performed using real-time ultrasonography
• Doctors under to outlined the placenta fluid

Chorionic Villus Sampling

• Biopsy of the tissue by needle and/or polyethylene catheter, done using a scope abdominally or transcervically
• Sampling for of assess with can be made
• A is made weeks
• CVS in is better chromosome can be determined is
• Carries a fetal loss of 0.5% to 1%.
• Advantage over that it can be carried out sooner with result are available quicker

Cell Cultures

• Chromosomal disorders prevail in 1 in 120 neonates
• Fetal and aberrations be be fetal in cells sampling
• microarray analysis used detecting
• Obtaining of cells by biopsy of the maturing by performing a biopsy of the maturing blastocyst for cell cultures
• Autosomal cases sex linked hemophilia and dystrophy
• Can now be detected using techniques such as fluorescence in situ hybridization technology
• Inborn errors of metabolism in fetuses can also be detected by studying cell cultures

Noninvasive Prenatal Diagnosis

• Trisomy 21/Down syndrome is the most common disease
• Based on the isolation of fetal cells in maternal blood and the detection of cell-free fetal DNA and RNA
• Recent sequencing technologies has prenatal diagnoses

Fetal Transfusion

• Treat with blood Injected/
• With blood cells been the to of with due to is nowadays by given is and
• Recent blood may be transfuse directly for anemia

Fetoscopy

• Fiber-optic instruments
• Fetoscope is inserted through moms abdomen
• Laser coagulation fixes transfusion. Used to fix amniotic bands
• Twin-twin transfusion can be fixed via laser coagulation

Blood Sampling

• Used for for conditions and for anemia and for fetal infection
• Ultrasound the vessels pregnancy loss a of

Magnetic Resonance Imaging

• Provides More ultrasonic Defects Not has higher and
• May provide important advantages over ultrasound such as higher soft tissue contrast and resolution

Fetal Monitoring

• Occurs in high
• Information occurs is that there are maternal
• Is rate and distress
• distress is by the fetus is in non-invasive method uses the moms