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My name is Errol Norwitz.
I am associate professor of obstetrics and
Yale University School of Medicine.
Co-director of the division of
Maternal Fetal Medicine and Director of
the Maternal Fetal Medicine Fellowship
Program in the Department of Obstetrics,
Gynecology and Reproductive Sciences
at Yale, New Haven Medical Center.
The topic for our discussion today
is the endocrinology of parturition.
Objectives over the next 40 to 50 minutes
are to understand in detail the molecular
and cellular mechanisms responsible for
the onset of labor at term.
To appreciate how and
why these mechanisms occasionally fail,
leading to pre-term birth or
And to discuss the rationale
behind interventions designed to
prevent and/or treat
abnormalities of labor.
Labor is the physiological process
by which the products of conception
are passed from the uterus to the outside
world, and is common to all viviparous
species labor even in this day and age
remains a clinical diagnosis characterised
by regular painful uterine contractions
increasing in frequency and
intensity associated with progressive
cervical effacement and dilatation
leading ultimately to the expulsion of
the products of conception in normal
labor there appears to be a time dependent
relationship between these factors.
The biochemical connective tissue changes
in the cervix usually precedes uterine
contractions and cervical dilatation,
which in turn occurs before spontaneous
rupture of the fetal membranes.
Similarly, pro-contractile biochemical
changes in the uterus precede active and
effective uterine contractions.
Cervical dilatation in the absence of
uterine contractions is seen most commonly
in the second trimester and
is suggestive of cervical insufficiency or
Similarly, the presence of uterine
contractions in the absence of cervical
change does not meet criteria for
the diagnosis of labor and
should be referred to as
Of note, a diagnosis of labor can
be made in nulliparous patient in
the setting of regular painful
uterine contractions if the initial
cervical examination is greater than or
equal to 80% effacement or
greater than or
equal to two centimeters dilatation.