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)
