Physiologic Adaptations at Birth
Ma. Luisa de Villa-Manlapaz, MD, MHPEd
February 8, 2011
ASMPH
Learning Objectives
- To review the fetal circulation
- To learn the changes in the pulmonary and cardiovascular system that
occur during birth
- To learn the hepatic adaptations in glucose metabolism, bilirubin
metabolism, and vitamin K production
- To learn how a newborn achieves thermoregulation
Fetal Circulation
- Placenta is responsible for exchange of gases, nutrients and metabolic
waste products
- Fetus receives blood from the placenta and returns it to the placenta
- Blood flows from the placenta into the umbilical vein
- The blood which contains a PO2 of approx 35 mmHg passes through the
liver and ductus venosus
- Blood from ductus venosus drains into the inferior vena cava  foramen
ovale  left atrium
- Superior vena cava drains de-oxygenated blood from the brain into the
right atrium.
-  right ventricle.
- 90% of blood from RA shunted through the ductus arteriosus
- 10% ejected to pulmonary artery  lungs
Fetal Lungs and Circulation
- Alveoli filled with lung fluid
- Pulmonary arterioles constricted
- Pulmonary blood flow diminished
Neonatal Circulation
- After birth, umbilical cord is cut
- Systemic vascular resistance increases (BP in aorta increases)
- Pulmonary vascular resistance decreases (BP in lungs decreases)
Lungs and Circulation After Delivery
- Lungs expand with air
- Fetal lung fluid leaves alveoli
Lungs and Circulation
- Pulmonary arterioles dilate
- Pulmonary blood flow increases
- Blood oxygen levels rise
- Ductus arteriosus constricts
- Blood flows through lungs to pick up oxygen
Normal Transition
- Fluid in alveoli absorbed and replaced by air
- Umbilical arteries and vein constrict thus increasing blood pressure
- Blood vessels in lungs relax, increasing pulmonary blood flow
- Baby cries and take first breath which help open alveoli
- Surfactant keeps the alveoli from collapsing after they expand
Metabolic Adaptation
- In utero, fetus relies primarily on placental transfer of glucose and
nutrients from mother to meet energy demands
Metabolic Adaptation
- Fetus stores glucose in the form of glycogen in last trimester – especially
in last month of trimester
After Birth
- Enzymes activate breakdown of glycogen back into glucose molecules
- Glucose released into bloodstream to maintain blood sugar
- Normal glucose utilization rate in fasting healthy term infant is 4-6
mg/kg/min
o Factors which influence glucose levels
o Glycogen stores
o Insulin levels
o Glucose utilization
o Premature baby
o Infant of diabetic mother
o Sick infant
Note: Different from the slide; slide had no heading, decided to place it as a subbullet since they are related (slide 16-17)
Thermoregulation
- In utero, the fetus is in a warm and dark environment
- Temperature is controlled
- At birth, newborn has to produce as much heat as much as is lost
- THERMOREGULATION
Normal Response to Cold Stress
- Vasoconstriction in arms and legs
- Increased movement and flexion of extremities
- Brown fat metabolism
Brown Fat Metabolism
Heat loss
Occurs on a gradient from warmer to cooler
Baby’s warm body to cooler air or surface
-
Head loss accentuated by:
o Wet skin
o Cool air temperature
o Drafts
Kangaroo mother care
- Mother provides warmth to the baby by skin to skin contact
- Provides easy access to the breasts, promoting breastfeeding
Hepatic adaptation
- Minor role of fetal liver – portal circulation shunted through the ductus
venosus
- Majority of bilirubin pigment transferred unaltered across the placenta to
the maternal circulation
- Fetus has a high percentage of circulating red blood cells to utilize all
available oxygen in a low oxygen environment
PHYSIOLOGIC JAUDICE
- Increased bilirubin load on liver cell
o Increased erythrocyte volume
o Decreased erythrocyte survival
o Increased enterohepatic circulation of bilirubin
- Immature liver function
Hepatic Adaptation
- Liver manufactures clotting factors needed for blood coagulation
- Several factors need Vitamin K for their production
- Bacteria that produce Vitamin K are normally found in the
gastrointestinal tract
- However, the gastrointestinal tract of the newborn is sterile
- Therefore newborn cannot manufacture vitamin K which is needed to
produce some clotting factors
- Newborns are given Vitamin K either intramuscularly or orally at birth to
prevent bleeding disorders
Learning Objectives
- To review the fetal circulation
- To learn the changes in the pulmonary and cardiovascular system that
occur during birth
- To learn the hepatic adaptations in glucose metabolism, bilirubin
metabolism, and vitamin K production
- To learn how a newborn achieves thermoregulation
Note: Repeated from the beginning
Brazelton’s States of Reactivity
1. Deep sleep: quiet, non-restless sleep state
2. Light sleep: eyes closed but more activity is noted; newborn moves actively;
may show sucking behaviour
3. Drowsy: eyes open and close and eyelids look heavy; body activity is present
with episodes of fussiness
4. Quiet alert: quiet state with little body movement, but the newborn’s eyes are
open and she is attentive to people and things that are near her
5. Active alert: eyes are open and active body movements are present; newborn
responds to stimuli actively
6. Crying: eyes may be tightly closed, thrashing movements are made together
with active crying