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Fetal Terminology
  • Ovum: ovulation to fetilization
  • Zygote: Fertilization to implantation
  • Embryo: implantation to 5-8 wks
  • Fetus: from 5-8 wks until term
Fertilization
  • Is the beginning of pregnancy
  • The union of the ovum and spermatoza
  • occurs at the outer third of the fallopian tube
 
Implantation
  • occers when the zygote contacts the uterine endometrium
  • occurs 8-10 days after fertilization
  • may cause implantation spotting
Embryonic and Fetal Structures
  • The endometrium becomes the decidua
  • the corpus lutem supplies hormones until the placenta takes over at 12 wks
  • Chorionic villi: "fetal capillaries" procues hormones, protect fetus >200 by term
  • Placenta: arises from the trophoblastic tissue, serves as lungs, digestion, and elimination for fetus.
 
The Placenta
  • Takes over hormone production at 12 weeks
  • placental/umbilical size is relative to size of baby
Placental Hormones
  • HCG: high till 100th day, ensures the corpus lutem pushes out hormones until placenta takes over, suppresses mother immunologic response
  • Estrogen: contributes to mammary gland development for lactation, stimulates uterine growth to accomodate fetus
  • Progesterone: maintains endometrial lining (prevents sloughing), reduces contractility of uterus
  • Human placental lactogen: promotes lactation, preps breast, regulates maternal glucose
Umbilical Cord
  • Fetal membrane (amnion/chorion)
  • provides a circulatory pathway
  • contains one vein and two arteries surrounded by wharton's jelly
  • can be sampled for fetal ABGs via PUBS (percutaneous umbilical blood sampling)
  • no nerve supply
  • missing vasculature can indicate fetal defects (especially kidneys)
  • O2 is carried in the vein
  • normally 18-22 inches long
 
Amniotic Membrane
  • Chorion: outer membrane: supports the sace that contains amniotic fluid
  • Amnion: inner membrane,, produces amniotic fluid
  • produces phospholipds→prostaglandins which help promote lung maturity and cause uterine contractions
Amniotic Fluid
  • never stagnant (usally clear/odorless)
  • constantly being formed, swallowed by fetus, and urinated back out
  • 800-1000 ml by term
  • Hydroaminos: > 2000 ml, benign if idopathic, more common in DM, can be d/t Gi defect
  • Oligohydraminos: < 300 ml, can be d/t poor fetal kidney function, can cause hypoxia, ↓ lung maturation, or structural defects d/t lack of cushioning
 
Amniotic Fluid Functions
  • protects the fetus and allows movement
  • shields against pressure
  • protects against temp changes
  • protects umbilical cord from pressure
  • pH 7.2 compared to urine @ 5.0-5.5
Development of Organs
  • stem cells: undifferentiated for 4 days
  • zygote growth is encephalocaudal (head to tail)
  • Primary germ layers: ectoderm (CNS, skin, hair, nails), mesoderm (connective tissues, kidneys/ureters, reproductive, heart, corculatory, lymph), entoderm: (linings of cavities, parathyroid, thyroid, thymus, bladder/urethra)
  • Organogenesis
  • Teratogens (etoh, drugs, meds, enviromental)
Fetal Circulation
  • no oxygenation to lungs
  • shunts to important organs close at birth
  • ductus venosus: allows blood flow to liver
  • foramen ovale: between atria
  • ductus arteriosus: beteween plumonary artery/aorta
Fetal HGB
  • Differnet from adult HGB
  • may develop defects and it convers to adult leading to blood dyscrasias
  • conversion to adult hgb usally by 6 months of age
  • has a greater affinity for O2
  • blood pH is normal down to 7.20
Respiratory System
  • is of concern in preterm infants: <22 week=death
  • diaphragmatic hernia: diaphragm fails to close 50/50 survival rate
  • capillary and alveoli develop between 24-28 weeks
  • surfactant starts forming at 24 weeks
  • Lecithin and sphingomyelin (2:1 ratio suggets maturity)
  • prostaglandins: present or absent, more reliable than LS ratio
Nercous and Endocrine Systems
  • develops as early as 3 weeks
  • no ETOH
  • folic acid important to prevent neural tube defects (0.4 mg-1.0 mg/day)
  • pancreas makes insuling needed by fetus
  • maternal insulin does not cross placenta
  • maternal DM ↑ risk for fetal hypoglycemia at birth
  • Gestational DM increses risk for type 2 DM
GI system
  • resp and GI tracts start out as a single tube, and once seperated can cause anomolies
  • cells that shed from the tract make up part of the meconium
  • abdominal contents extend into the umbilical cord early in development
GI cont.
  • Problems: volvulus, meckel's diverticulum
  • GI tract is sterile, so no bacteria for vit K production
  • suck and swallow reflexes not mature till 32 wks
  • enzymes for cho and protein digestion mature at 36 weeks
  • liver is still immature at birth, can cause hypoglycemia and hyperbillirubinemia
Musculoskeletal
  • Quickening around 20 weeks
  • movement starts at 11 weeks
  • kick counts: time for 10 kicks or # in an hour (should be > 10)
Reproductive
  • sperm carries X or Y chromosome for determining gender
  • males: testes secrete testosterone to support development of male organs
  • without testosterone, female organs develop
 
Kidneys
  • not needed before birth because placenta does the work
  • forms urine by the 12th wk which is excreted into amniotic flulid by 16th wk
  • makes about 500 ml/day by birth
  • the amount of amniotic fluid is affected by amount of urine produced
  • continutes to mature after birth
Integumentary System
  • skin is thin/almost transparent until sub-q fat is deposited around 36 wks
  • covered in lanugo (insulation) and vernix caseosa (keeps babies from wrinkling in amniotic fluid)
  • avoid tape and adhesives
  • babies at < 36 weeks at risk for heat loss, dehydration, infection)
   
Immune System
  • IgG antibodies cross the placenta for passive immunity
  • No immunity to herpes virus
  • immunizations begin by 2 months of age (DPT, polio, flu)
  • passive immunity to measles lasts longer, give at 12 months
Estimated Birth Date
  • EDC: estimated date of confinement
  • EDB: estimated date of birth
  • EDD: estimated date of delivery
  • Nagles Rule: LMP - 3 months + 7 days
Assessment of fetal growth
  • Health History
  • McDonald's Rule: symphysis-fundal height measurement in CM is equal to weeks of gestation between 20-31 weeks
How to assess fetal well being
  • fetus moves at least 10 times/day
  • causes of decreased movement
  • kick counts: 10/hr
FHR
  • FHR: 120-160
  • establish the baseline
  • can be short term or long term variability
 
Non stress test (NST)
  • can be done at home
  • mother pushes a button every time the baby moves
  • FHR should incrase by 15 bpm and remain eleveated for 15 seconds
  • reactive if accelerations occur (good)
  • non reactive if accelerations do not occur (bad)
  • OJ/cold liquid or loud sounds can stimulate baby
  • reactive test means baby is probably good for another week
Contraction Stress Test
  • FHR is analyzed during contractions
  • nipple stimulation release endogenous oxytocin, or IV oxytocin
  • test is negative if no FHR decels during contraction
  • positive if 50% or more contractions cause a late decel
   
Ultrasound
  • used to assess fetal structures
  • procedure: full bladdes, abd exposed, use of gel
  • does not involve x-rays
  • can take a picture to bring home
Diagnostic Studies
  • AFP
  • Triple Screen: estrodiol, HcG, AFP
  • CVS
  • Amniocentesis
  • PUBS
  • FNT (fetal nuchal translucency)
  • Level II ustrasuond/ fetal scan
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