Frederick R. Jelovsek MD
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.
| 
