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Preterm labor is the onset of uterine contractions prior to 37
weeks’ gestation. Preterm deliveries are the major contributors
to infant mortality. The rate of preterm delivery has increased
despite intensive efforts to identify causes and develop treatments. The
problem of prematurity includes multiple pathologies. Very early
preterm deliveries prior to 28 weeks’ gestation are less
than 1% of the deliveries but are the major association
with infant mortality. Many of the deliveries are associated with both
preterm premature rupture of membranes and chorioamnionitis, an inflammation
of the fetal membranes and chord.8 These early
deliveries seem to be associated with low-grade pathogens such as Ureaplasma or Mycoplasma. Later
gestation preterms are frequently medically indicated because the
women have preeclampsia, fetal growth restriction, or multiple births.
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The risks to the preterm born before 32 to 34 weeks’ gestation
can be decreased by treating the woman with antenatal corticosteroids. This
treatment effectively decreases the risk to the preterm newborn
of respiratory distress syndrome, intraventricular hemorrhage, and death.9 There
are essentially no contraindications to a single maternal course
of antenatal corticosteroids. However, optimal fetal responses require
a treatment to delivery interval of about 48 hours. Therefore, women
at risk of early preterm delivery should be treated with corticosteroids
at the first recognition of preterm labor or prior to an elective
delivery for preeclampsia, for example. Women with early preterm
labor are routinely treated with antibiotics because of the risk
of infection, but women at high risk of preterm delivery do not
benefit from routine antibiotic treatments.
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Once preterm labor has started, attempts are often made to stop
the labor and delay delivery using a variety of drugs that interfere
with the labor processes. These drugs include indomethacin, calcium
channel blockers, beta agonists, and magnesium sulfate. No agent
has proved to be consistently effective at stopping preterm labor,
and each agent has toxicities for the woman and the fetus. In general,
short-term use of agents to stop labor—tocolysis—may
have some benefit, but long-term use may have little benefit.
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The majority of the morbidities occur in very preterm infants,
although most preterm infants are born between 32 and 36 completed weeks
of gestation. These infants are often considered to be normal. However,
they have significant problems with neonatal adaptation: transient
respiratory distress, inadequate temperature regulation, hyperbilirubinemia,
and feeding difficulties.10 The neurodevelopmental
outcomes also are not equivalent to a term population. This population
of late-preterm infants is increasing. Late-preterm deliveries should
be avoided if at all possible.
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The frequency of multiple births has increased primarily because
of assisted reproductive technologies. The occurrence of multiples
is proportionate to the number of embryos transferred and to the
use of multiple ovulation agents such as Clomid. Multiple births
should be avoided because fetal outcomes are less favorable for
multiples relative to singletons. In general, most twins deliver
close to term, but higher multiples deliver at earlier gestations. Disparate
fetal growth is frequent and can result in preterm delivery. The
majority of twins and higher multiples are delivered by cesarean section
to avoid complications resulting from delivery of the second infant.
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This enigmatic disease occurs in 7% to 10% of pregnancies
in the United States. Despite intensive study, the cause of the
disease remains unknown.11 Preeclampsia is a syndrome
arbitrarily divided into mild and severe forms. Mild preeclampsia
is diagnosed by a 30-mm Hg increase in systolic or a 15-mm Hg increase
in diastolic blood pressure and proteinuria. Diagnosis of severe
preeclampsia requires one of the following: worsening hypertension,
severe proteinuria, oliguria, central nervous system symptomatology, pulmonary
edema, liver functional abnormalities, fetal growth restriction,
and other abnormalities. Seizures with preeclampsia define eclampsia.
The syndrome results from vasoregulatory abnormalities in the placenta
and in the pregnant woman. Magnesium sulfate is used to decrease
the risk of seizures, and multiple agents are used to control blood
pressure. Mild preeclampsia can be carefully monitored, but progressive
disease requires delivery of the fetus, which cures the syndrome.
If preeclampsia occurs at a gestational age earlier than 34 weeks,
maternal corticosteroid therapy should be given with delay of delivery
for 48 hours if possible. The outcome of the pregnancy with preeclampsia
is generally favorable with careful monitoring if the infant is
not too preterm. In the developing world, preeclampsia is a major
cause of maternal and fetal death.