DYSTOCIA & ABNORMAL FETAL PRESENTATIONS & POSITIONS
A prolonged latent phase by definition exceeds 20 h in a nulliparous
parturient and 14 h in a multiparous patient. The cervix usually remains at 4
cm or less but is completely effaced. The etiology is likely ineffective
contractions without a dominant myometrial pace-maker. Arrest of dilation is
present when the cervix undergoes no further change after 2 h in the active
phase of labor. A protracted active phase refers to slower than normal cervical
dilation, defined as less than 1.2 cm/h in a nulliparous patient and less than 1.5
cm/h in a multiparous parturient. A prolonged deceleration phase occurs when
cervical dilation slows markedly after 8 cm. The cervix becomes very edematous
and appears to lose effacement. A pro-longed second stage (disorder of descent)
is defined as a descent of less than 1 cm/h and 2 cm/h in nul-liparous and
multiparous parturients, respectively. Failure of the head to descend 1 cm in
station after adequate pushing is referred to as arrest of descent.
Oxytocin is usually the treatment of choice
for uterine contractile abnormalities. The drug is given intravenously at 1–6
mU/min and increased in incre-ments of 1–6 mU/min every 15–40 min, depending on
the protocol. Use of amniotomy is controversial. Treatment is usually expectant
management, as long as the fetus and mother are tolerating the prolonged labor.
When a trial of oxytocin is unsuccessful or when malpresentation or
cephalopelvic dispropor-tion is also present, operative vaginal delivery or
cesarean section is indicated.
Breech presentations complicate 3–4% of
deliveries and significantly increase both maternal and fetal morbidity and
mortality rates. Breech presentations increase neonatal mortality and the
incidence of cord prolapse more than 10-fold. External cephalic version may be
attempted after 34 weeks of gestation and prior to the onset of labor; however,
the fetus may spontaneously return to the breech presenta-tion before the onset
of labor. Some obstetricians
may administer a tocolytic agent at the same
time. External version can be facilitated, and its success rate improved, by
providing epidural analgesia with 2% lidocaine and fentanyl. Although an
external version is successful in 75% of patients, it can cause placental
abruption and umbilical cord compression necessitating immediate cesarean
section.
Because the shoulders or head can become
trapped after vaginal delivery of the body, some obstetricians employ cesarean
section for all breech presentations. Manual or forceps-assisted partial breech
extraction is usually necessary during these vaginal deliveries. The need for
breech extraction does not appear to be increased when epidural anes-thesia is
used for labor—if labor is well established prior to epidural activation.
Moreover, epidural anesthesia may decrease the likelihood of a trapped head,
because the former relaxes the perineum. Nonetheless, the fetal head can become
trapped in the uterus even during cesarean section under regional anesthesia;
rapid induction of general endo-tracheal anesthesia and administration of a
volatile agent may be attempted in such instances to relax the uterus.
Alternatively, nitroglycerin, 50–100 mcg intravenously, can be administered.
When the fetal occiput fails to spontaneously rotate anteriorly, a
persistent occiput posterior presenta-tion results in a more prolonged and
painful labor. Manual, vacuum, or forceps rotation is usually necessary but
increases the likelihood of maternal and fetal injuries. Regional anesthesia
can be used to provide perineal analgesia and pelvic relaxation, allowing
manual or forceps rotation followed by for-ceps delivery.
A face presentation occurs when the fetal head is hyperextended and
generally requires cesarean section. A compound presentation occurs when an
extremity enters the pelvis along with either the head or the buttocks. Vaginal
delivery is usually still possible because the extremity often withdraws as the
labor progresses.
Shoulder dystocia, or impaction of a shoulder against the pubic
symphysis, complicates 0.2–2% of deliveries and is one of the major causes of
birth injuries. The most important risk factor is fetal macrosomia. Shoulder
dystocias are often difficult to predict. Several obstetric maneuvers can be
used to relieve it, but a prolonged delay in the delivery could result in fetal
asphyxia. Induction of general anesthesia may be necessary if an epidural
catheter is not already in place.
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