OB Exam 2
Labor and Childbirth
Initiation of Labor pg. 456
It is believed that labor is influenced by: uterine stretch from the fetus and amniotic fluid
volume, progesterone withdrawal to estrogen dominance, increase oxytocin sensitivity, and
increased release of prostaglandins
Estrogen to progesterone ratio
oDuring the last trimester estrogen increases and progesterone decreases
The number of oxytocin receptors in the uterus increases at the end of pregnancy
Increased levels of estrogen also lead to increased sensitivity to oxytocin
With increasing oxytocin levels in the maternal blood along with increasing fetal cortisol
levels that synthesize prostaglandins, uterine concentrations are initiated
Oxytocin also aids in stimulating prostaglandin synthesis
Prostaglandins lead to additional contractions, cervical softening, gap junction induction,
and myometrial sensitization leading to progressive cervical dilation
Uterine contractions have two main functions: dilate the cervix and to push the fetus
through the birth canal
Signs of Approaching Labor pg. 456
Lightening occurs when the fetal presenting part begins to descend into the true pelvis
oThe uterus lowers and moves into a more anterior position
oThe woman will usually notice her breathing becomes much easier and there is
decreased gastric reflux
oShe may complain of increased pelvic pressure, leg cramping, dependent edema in
the lower legs, low back discomfort, increase in vaginal discharge and urination
oIn primiparas, lightening can occur 2 weeks or more before labor beings and in
multiparas, it may not occur until labor
Braxton Hicks Contractions may be experienced throughout the pregnancy
oFelt as tightening or pulling sensation on top of the uterus
oOccur primarily in abdomen and groin and gradually spread downward before
relaxing
oIrregular contractions that can be decreased by walking, voiding, eating, increasing
fluid intake, or changing position
oUsually last about 30 seconds but can last up to 2 minutes
oAs birth gets closer, the uterus becomes more sensitive to oxytocin and the
frequency and intensity of these contractions increases
oIf the contractions last longer than 30 secs and occur more than 4-6x/hr, the woman
should contact her HCP so she can be evaluated for preterm labor
Backache
Bloody show
oAt the onset of labor or before, the mucous plug that fills the cervical canal is
expelled as a result of cervical softening and increased pressure of the presenting
part
, oThese ruptured capillaries release a small amount of blood that mixes with mucus
resulting in the pink tinged secretions known as the bloody show
Spontaneous Rupture of Membranes
oRupture of membranes with loss of amniotic fluid prior to onset of labor
premature rupture of membranes (PROM)
oThe majority of women will begin labor within 24 hours
oThe rupture can result in either a sudden gush or a steady leakage of amniotic fluid
oA continuous supply of amniotic is produced even though some is lost
oAfter the amniotic sac has ruptured, the barrier to infection is gone and ascending
infection is possible
oThere is also a danger of cord prolapse if engagement has not occurred
Increased Energy Level
oSome women have a sudden increase in energy before labor
oSometimes this is referred to as nesting because the mother will use this time to
prepare for the baby and spend time with other children
oUsually occurs 24-48 hours before the onset of labor
oThought to be the result of an increase in epinephrine released caused by decreased
progesterone
Weight loss loses 1-3lbs
True vs. False Labor pg. 457
False labor irregular uterine contractions are felt but the cervix is not affected
oFalse labor, prodromal labor, Braxton Hicks
True labor contractions occurring at regular intervals that increase in frequency,
duration, and intensity
oBring about progressive cervical dilation and effacement
Example: if a woman comes in and she goes from 2cm to 3 cm then back to 2cm and stays
that way for hours, you would send her home because it’s not progressing
Cervical Dilatations and Effacement
Dilatation is the opening of the cervix
Effacement is the thinning of the cervix
,Theories of Onset of Labor
Oxytocin production
Prostaglandin
Estrogen stimulation
Fetal influences
Others
“P’s” of Labor pg. 458
Passageway (birth canal)
Passenger (fetus and placenta)
Powers (contractions)
Position (maternal)
Psychological response
Passageway pg. 458
Have to make sure the baby can come out
The birth passageway is the route through which the fetus must travel to be born vaginally
The passageway way consists of the maternal pelvis and soft tissues
The pelvis is the most important and it is typically assessed and measured during the first
trimester to identify any abnormalities that might hinder vaginal birth
Relaxin and estrogen cause the connective tissues to become more relaxed and elastic and
cause the joints to be more flexible to prepare the mother’s pelvis for birth
Bony Pelvis
The maternal bony pelvis can be divided into the true and false portions
The false part is the upper part and the true pelvis is the bony passage through which the
fetus must travel
, oMade up of: the inlet, the mid-pelvis (cavity), and the outlet
To ensure the adequacy of the pelvic outlet for vaginal birth, these measurements are
assessed:
oDiagonal conjugate of the inlet (distance between the anterior surface of the sacral
prominence and the anterior surface of the inferior margin of the symphysis pubis)
oTransverse or ischial tuberosity diameter of the outlet (distance at the medial and
lowest aspect of the ischial tuberosities, at the level of the anus, a known hand span
or clenched-fist measurement is generally used to obtain this measurement)
oTrue or obstetric conjugate (distance estimated from the measurement of the
diagonal conjugate; 1.5cm is subtracted from the diagonal conjugate measurement)
If the diagonal conjugate measures at least 11.5cm and the true or obstetric conjugate
measures 10cm of more (1.5cm less than diagonal conjugate, or about 10cm), then the
pelvis is large enough for vaginal birth of what would be considered a normal sized newborn
Pelvic Shape
The shape is a determining factor of a woman’s pelvis in addition to size
Each plane of the pelvis has a shape, which is defined by the anterior-posterior and
transverse diameters
Gynecoid Pelvis
oConsidered the true female pelvis 40% of women
oVaginal birth is most favorable with this type because the inlet is round and the
outlet is roomy
oOptimal diameters in all 3 planes of the pelvis
oAllows early and complete fetal internal rotation during labor and the sacrum is
long, producing a deep pelvis
oVaginal birth is more favorable with the pelvic shape compared with android or
platypelloid shape
Anthropoid Pelvis
oMost common in men and most common in non-white women 25% of women
oThe pelvic inlet is oval
Android Pelvis
oConsidered the male shaped pelvis and is characterized by a funnel shape 20% of
women
oThe pelvis inlet is heart shaped and the posterior segments are reduced in all pelvic
planes
oDescent of the fetal head into the pelvis is slow and failure of fetus to rotate is
common
oPrognosis is poor and usually leads to c-section
Platypelloid (flat) Pelvis
oLeast common type 3% incidence
oPelvic cavity is shallow but widens at the pelvic outlet, making it difÏcult for the
fetus to descend through the mid-pelvis
oLabor prognosis is poor with arrest in the inlet occurring frequently usually
require c-section
Labor and Childbirth
Initiation of Labor pg. 456
It is believed that labor is influenced by: uterine stretch from the fetus and amniotic fluid
volume, progesterone withdrawal to estrogen dominance, increase oxytocin sensitivity, and
increased release of prostaglandins
Estrogen to progesterone ratio
oDuring the last trimester estrogen increases and progesterone decreases
The number of oxytocin receptors in the uterus increases at the end of pregnancy
Increased levels of estrogen also lead to increased sensitivity to oxytocin
With increasing oxytocin levels in the maternal blood along with increasing fetal cortisol
levels that synthesize prostaglandins, uterine concentrations are initiated
Oxytocin also aids in stimulating prostaglandin synthesis
Prostaglandins lead to additional contractions, cervical softening, gap junction induction,
and myometrial sensitization leading to progressive cervical dilation
Uterine contractions have two main functions: dilate the cervix and to push the fetus
through the birth canal
Signs of Approaching Labor pg. 456
Lightening occurs when the fetal presenting part begins to descend into the true pelvis
oThe uterus lowers and moves into a more anterior position
oThe woman will usually notice her breathing becomes much easier and there is
decreased gastric reflux
oShe may complain of increased pelvic pressure, leg cramping, dependent edema in
the lower legs, low back discomfort, increase in vaginal discharge and urination
oIn primiparas, lightening can occur 2 weeks or more before labor beings and in
multiparas, it may not occur until labor
Braxton Hicks Contractions may be experienced throughout the pregnancy
oFelt as tightening or pulling sensation on top of the uterus
oOccur primarily in abdomen and groin and gradually spread downward before
relaxing
oIrregular contractions that can be decreased by walking, voiding, eating, increasing
fluid intake, or changing position
oUsually last about 30 seconds but can last up to 2 minutes
oAs birth gets closer, the uterus becomes more sensitive to oxytocin and the
frequency and intensity of these contractions increases
oIf the contractions last longer than 30 secs and occur more than 4-6x/hr, the woman
should contact her HCP so she can be evaluated for preterm labor
Backache
Bloody show
oAt the onset of labor or before, the mucous plug that fills the cervical canal is
expelled as a result of cervical softening and increased pressure of the presenting
part
, oThese ruptured capillaries release a small amount of blood that mixes with mucus
resulting in the pink tinged secretions known as the bloody show
Spontaneous Rupture of Membranes
oRupture of membranes with loss of amniotic fluid prior to onset of labor
premature rupture of membranes (PROM)
oThe majority of women will begin labor within 24 hours
oThe rupture can result in either a sudden gush or a steady leakage of amniotic fluid
oA continuous supply of amniotic is produced even though some is lost
oAfter the amniotic sac has ruptured, the barrier to infection is gone and ascending
infection is possible
oThere is also a danger of cord prolapse if engagement has not occurred
Increased Energy Level
oSome women have a sudden increase in energy before labor
oSometimes this is referred to as nesting because the mother will use this time to
prepare for the baby and spend time with other children
oUsually occurs 24-48 hours before the onset of labor
oThought to be the result of an increase in epinephrine released caused by decreased
progesterone
Weight loss loses 1-3lbs
True vs. False Labor pg. 457
False labor irregular uterine contractions are felt but the cervix is not affected
oFalse labor, prodromal labor, Braxton Hicks
True labor contractions occurring at regular intervals that increase in frequency,
duration, and intensity
oBring about progressive cervical dilation and effacement
Example: if a woman comes in and she goes from 2cm to 3 cm then back to 2cm and stays
that way for hours, you would send her home because it’s not progressing
Cervical Dilatations and Effacement
Dilatation is the opening of the cervix
Effacement is the thinning of the cervix
,Theories of Onset of Labor
Oxytocin production
Prostaglandin
Estrogen stimulation
Fetal influences
Others
“P’s” of Labor pg. 458
Passageway (birth canal)
Passenger (fetus and placenta)
Powers (contractions)
Position (maternal)
Psychological response
Passageway pg. 458
Have to make sure the baby can come out
The birth passageway is the route through which the fetus must travel to be born vaginally
The passageway way consists of the maternal pelvis and soft tissues
The pelvis is the most important and it is typically assessed and measured during the first
trimester to identify any abnormalities that might hinder vaginal birth
Relaxin and estrogen cause the connective tissues to become more relaxed and elastic and
cause the joints to be more flexible to prepare the mother’s pelvis for birth
Bony Pelvis
The maternal bony pelvis can be divided into the true and false portions
The false part is the upper part and the true pelvis is the bony passage through which the
fetus must travel
, oMade up of: the inlet, the mid-pelvis (cavity), and the outlet
To ensure the adequacy of the pelvic outlet for vaginal birth, these measurements are
assessed:
oDiagonal conjugate of the inlet (distance between the anterior surface of the sacral
prominence and the anterior surface of the inferior margin of the symphysis pubis)
oTransverse or ischial tuberosity diameter of the outlet (distance at the medial and
lowest aspect of the ischial tuberosities, at the level of the anus, a known hand span
or clenched-fist measurement is generally used to obtain this measurement)
oTrue or obstetric conjugate (distance estimated from the measurement of the
diagonal conjugate; 1.5cm is subtracted from the diagonal conjugate measurement)
If the diagonal conjugate measures at least 11.5cm and the true or obstetric conjugate
measures 10cm of more (1.5cm less than diagonal conjugate, or about 10cm), then the
pelvis is large enough for vaginal birth of what would be considered a normal sized newborn
Pelvic Shape
The shape is a determining factor of a woman’s pelvis in addition to size
Each plane of the pelvis has a shape, which is defined by the anterior-posterior and
transverse diameters
Gynecoid Pelvis
oConsidered the true female pelvis 40% of women
oVaginal birth is most favorable with this type because the inlet is round and the
outlet is roomy
oOptimal diameters in all 3 planes of the pelvis
oAllows early and complete fetal internal rotation during labor and the sacrum is
long, producing a deep pelvis
oVaginal birth is more favorable with the pelvic shape compared with android or
platypelloid shape
Anthropoid Pelvis
oMost common in men and most common in non-white women 25% of women
oThe pelvic inlet is oval
Android Pelvis
oConsidered the male shaped pelvis and is characterized by a funnel shape 20% of
women
oThe pelvis inlet is heart shaped and the posterior segments are reduced in all pelvic
planes
oDescent of the fetal head into the pelvis is slow and failure of fetus to rotate is
common
oPrognosis is poor and usually leads to c-section
Platypelloid (flat) Pelvis
oLeast common type 3% incidence
oPelvic cavity is shallow but widens at the pelvic outlet, making it difÏcult for the
fetus to descend through the mid-pelvis
oLabor prognosis is poor with arrest in the inlet occurring frequently usually
require c-section
