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.