The Perinatal Period:Transition from the Womb
Birth as a “non-event”
Neuro-behavioral systems functional prior to birth
develop in anticipation of need “forward reference” of Weissor “environment expectant”
For example,suckingswallowing“respiration”hiccupsyawning
So, other than constraints imposed bythe intra-uterine environment (e.g. fetusescannot cry without air), there is littlebehavioral difference between a late-termfetus and a newborn
What distinguishes a newborn froma fetus is that these behaviors areNECESSARY for survival
For example, “breathing” is not functionalas respiration in the fetus, but is essentialto the newborn.
How is initiation of breathing assured?
1. Temperature change is a noxious stimulus
2. Anoxia produced by clamping umbilical cord
3. Fluid is expelled from lungs during delivery, the remainder quickly absorbed.
Spanking a newborn is not necessaryto initiate breathing, and birthing in warm water makes little sense from either a physiological or evolutionary perspective.
4. Changes in other sensory inputs
Similarly, sucking and swallowing areessential to the newborn, but have beenexpressed by the fetus.
About the only thing not apparent in thefetus that is expressed by the newborn is crying, which we will discuss later.
So from a neuro-behavioral perspective, birth really is a “non-event,” unlike,for example amphibian metamorphosis.
What about from a biological/comparativeperspective?
Are there biological markers of maturity that define birth?
What initiates birth?
Mother?
Fetus?
What is the signal?
Oxytocin stimulates uterine contractions, but what stimulates oxytocin release?
What initiates birth?
Surfactant Protein A (SF-A)
Production in mice begins at G17 d(birth at G19)
begins in humans ~G32 wk(birth at 40 wk)
“breathing” amniotic fluid releases SF-A into the fluid
SF-A is essential for respiration after birth
SF-A signals mother that fetal lungs are mature, stimulates labor
Other than the capacity for independent respiration, there is little relationship between maturity and birth/hatching.
Precocialborn in a relatively maturestate
Altricialborn in arelatively immaturestate
CAUDATE
CAUDATE
CORTEX
CORTEX
MEDULLA
MEDULLA
CEREBELLUM
CEREBELLUM
THALAMUS
THALAMUS
MIDBRAINMIDBRAIN
Bignall, K.E. (1974)Experimental Neurology,42, 566-573.