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Nursing School

The Fetus
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from class notes...

THE FETUS

 

- defined as the time between 8-10 weeks to birth

- less vulnerable to teratogens but they may still interrupt the functional development of the organs, especially the CNS d/t neural development continuing throughout fetal development & after birth

 

- Fetal Viability - fetus can survive outside the uterus - the earliest is about 20 weeks

- survival of the fetus depends on:

                - maturity of the CNS - for directing respirations & controlling body temperature

                - maturity of the lungs - r/t organ development & production of surfactant

 

- Fetal Circulation - because lungs are not functional in utero, fetal circulation contains special vessels that shunt the blood around the lungs w/only a small amount circulating through the lungs for nutrition

                - fetal circulation is characterized by 5 special fetal vessels/structures:

                                - Umbilical Vein

                                - Ductus Venosus

                                - Foramen Ovale

                                - Ductus Arteriosus

                                - Umbilical Arteries

 

- from the placenta oxygenated blood travels through the Umbilical Vein (has the highest O2 content of fetal circulation) & passes through the inferior vena cava (on the way to the inferior vena cava it branches off into 2 parts - some goes to the liver but most passes through the Ductus Venosus

- from the inferior vena cava blood flows into the Right atrium & then directly into the Left atrium through the special fetal structure called the Foramen Ovale

- blood then enters the Left ventricle & leaves the heart through the aorta

                - blood that circulates up the arms & to the head returns through the superior vena cava, through the Right atrium again, then is deflected downward into the Right ventricle & out through pulmonary arteries

                - part of this blood goes to the lungs, but most goes to the aorta through the Ductus Arteriosus

- blood in the aorta, w/the exception of that going to the head/upper extremities, passes downward to supply the trunk & lower extremities

- most blood finds its way through the internal iliac arteries & back through the cord to the placenta by way of Umbilical Arteries where it is oxygenated again

- a small of blood passes back into the ascending vena cava, to mingle w/fresh blood & circulates again through the entire body

 

**Cephalocaudal (proximal/distal) law of Development:

- first thing newborns can do is lift their heads

- motor development is gross to fine, d/t blood flow

- development is head to toe; newborns control hands then fingers; walking comes after sitting, crawling, standing, etc...

 

 - As soon as a baby is born & breathes room air, fetal circulation is no longer necessary d/t proper lung function

- this change alters the character of blood in vessels & makes many fetal vessels useless - they close functionally & anatomically

- Functional Closure occurs first, in first few minutes/hours after birth

- Anatomic Closure vessels degenerate or become something else

                - Umbilical Vein fills w/clotted blood & is converted into fibrous cord; becomes round ligament of liver (takes about 3 months)

                - Umbilical Arteries fill w/clotted blood & are converted into fibrous cord; takes about 2 months

                - Foramen Ovale after cord is cut, a large amount of blood returns to the heart & lungs, causing equal pressure in right & left atria, causing the foramen ovale to close - it remains closed & degenerates; takes up to a year

                - Ductus Arteriosus & Venosus shrivel up & are converted into fibrous cord & ligaments; takes 2-3 months

 

 

- Fetal Evaluation to detect abnormalities &/or evaluate condition of fetus

                - fetal age assessment can be through ultrasound: will do this all 3 trimesters, measure diameter of fetal head, length of femur, abdominal circumference & head circumference - "crown to rump"

                - Nagel's Rule - ask mom when was the first day of your last period? & count back 3 months & add 7 days = estimated date of confinement (due date)

                - Ultrasound - movement will confirm life or death, structural development, # of babies, placental maturation & location, position of fetus, fetal heart activity (starting at 6-7 weeks), fetal age

                - Amniocentesis - around 14 weeks, diagnosis of genetic problems such as Down syndrome, or fetal hemolytic disease; can estimate fetal maturity (lung maturity); is invasive, is done under ultrasound, involves risk to fetus & mom

                - CVS - Chorionic Villus Sampling - around 10-12 weeks, done to detect genetic problems; risk for fetus & mom; is invasive, done either abdominally or vaginally

                - Non-Stress Test - if you're running late - after 40 weeks placenta is old & doesn't function as well, this checks on well being of baby; mom is connected to external fetal heart monitor & when baby moves HR should accelerate; if baby is sleeping mom is given juice to raise blood glucose, distend mom's stomach, & wake the baby to make it move; usually takes about 20 minutes; also done if there's a history of still births or diabetes mellitus or renal disease

                - AFP - alphafetoprotein screening - maternal blood test; AFP is predominate protein in fetal plasma produced in yolk sac during 1st 6 weeks of gestation, diffuses from fetal plasma into fetal urine & is excreted into amniotic fluid - crosses placental membrane into maternal circulation - done at 16 weeks as a screening test; if too high or too low other tests will be done

                - Biophysical Profile - similar to ultrasound, done under ultrasound, takes 30 minutes, measures 5 variables scored from 0-2

                                - fetal breathing movements (movements of chest wall, usually while swallowing)

                                - gross body movement

                                - fetal tone (flexion/extension of an extremity)

                                - amniotic fluid volume

                                - response (HR activity)

                - Contraction Stress Test - mom is connected to external fetal heart monitor; a healthy fetus can withstand a decrease in O2 during contractions - this test looks at HR of fetus during contractions; 2 types:

                                - Oxytocin (pitocin) Challenge Test - mom given IV pitocin to contract uterus, need 3 good contractions in 10 minutes to evaluate fetal response; not done too often d/t risk of inducing labor

                                - Nipple Stimulated Contraction Stress Test - mom massages her nipples to stimulate contractions (instead of using pitocin)

NOTHING on this website is to take the place of a physician's advice. Everything in this site is meant to be only a helpful tool for me and my nursing student friends.

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