Preterm births (less than 37 weeks gestation)
occur in 11% of all pregnancies. Births before 32
weeks gestation, however, account for most of the
newborn deaths and these occur in about 2% of pregnancies.
The incidence of preterm birth in the U.S. seems to
be slowly rising from about 9.5% to almost 11% in
the last 15 years. No one is sure why. Of all preterm
births, 50% result from spontaneous preterm labor,
30% from spontaneous rupture of the membranes, which
later proceeds into labor and 20% with maternal or
baby medical problems in which labor is induced early
for the benefit of the baby or mother.
A recent review, Goldenberg RL, Rouse DJ: Prevention
of preterm birth. N Engl J Med 1998;339(5):313-20,
points out that there is very little scientific evidence
that many of the treatments used to prevent preterm
birth are at all effective. They reviewed the literature
and commented on the traditional preterm birth prevention
interventions:
Interventions to Prevent Preterm Birth
Evidence of efficacy Intervention
No prenatal care (routine or enhanced)
No risk scoring systems
Yes cervical cerclage (for incompetent cervix)
Yes progestin supplementation (for history of preterm
labor
No programs for stopping tobacco, drug and alcohol
abuse
No psychological support
No nutritional counseling
No calorie supplementation
No protein supplementation
Uncertain vitamin or mineral supplementation
No patient education about preterm labor signs
No home uterine activity monitoring
No frequent contact with a nurse
Yes (48 hrs) tocolytic (medicines to stop contractions)
therapy
No bedrest (especially with twins)
No hydration
Yes screening for and treatment of
urinary tract infection or bacterial vaginosis
Yes antibiotics for preterm labor or premature rupture
of the membranes
No low dose aspirin
No calcium supplementation
Just because an intervention doesn't prevent preterm
delivery doesn't mean it shouldn't be used. Many of
the above interventions actually improve outcome by
causing increased fetal weight gain or increased lung
maturity at a given gestational age even though they
don't change the average weeks gestation at delivery.
Calorie supplementation helps if near starvation
conditions exist and smoking cessation causes babies
to weigh more. Remember at any gestational age, the
more a baby weighs the more likely the baby is to
survive. Antenatal care doesn't cause less preterm
births, but women who have more prenatal visits must
take care of themselves in other ways because they
will have a lower preterm delivery rate than women
who seek less antenatal care.
Many women have stories of how tocolytic medications
(terbutaline, ritodrine, magnesium sulfate) prevented
them from delivering early, but in fact there are
many studies indicating that they don't really prevent
labor for more than 48 hours. Similarly, the woman
who says "I had to be at bedrest" the entire
pregnancy, statistically, probably didn't. That doesn't
mean the bedrest didn't help the outcome; the baby
probably weighed more when it was born and thus had
a better chance at surviving and a lower chance at
acquiring some of the prematurity related problems,
but the time of delivery was probably what it would
have been if mother's activity had been unrestricted.
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