Preterm Labor
Prediction, Prevention,
and Management
Jennifer Hernandez, M.D.
Maternal-Fetal Medicine
Obstetrix Medical Group of Texas
Fort Worth, Texas
Objectives
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To review the background and epidemiology of
preterm birth
To discuss risk factors and screening methods
available for predicting women at risk and to
review preventative options for those women at
risk
To review how to diagnose preterm labor and
treatment options available for those women
To discuss preterm labor in multi-fetal gestations
and how these differ from singleton pregnancies
Overview
Preterm Birth: Background
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Preterm birth is defined as delivery prior to 37
completed weeks’ gestation
Early preterm birth is defined as delivery prior
to 34 weeks gestation
Late preterm birth is defined as delivery
between 34 0/7- 36 6/7 weeks’ gestation
Preterm birth can be due to PTL (40-45%),
PPROM (20-255%), or medically indicated
deliveries (30-35%)
Preterm Birth: Epidemiology
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The incidence of
preterm birth
increased more than
20% from 1990 to
2006
This was largely due
to a rise in multiple
gestations and
medically indicated
late preterm deliveries
Preterm Birth: Epidemiology
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Fortunately, the overall rate of preterm birth in the
United States is decreasing, down to 11.7 percent in
2011
This rate of preterm birth still remains higher than
other industrialized countries
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The U.S. ranks 131st out 184 countries with reported
rates of preterm birth
It’s not just a disparity between countries
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Vermont, New Hampshire, Oregon, and Maine all
have preterm birth rates < 9.6%
Louisiana, Mississippi, and Alabama all have rates
>14.6%
Preterm Birth: Significance
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Why does it matter?
Preterm birth is the leading cause of neonatal
morbidity and mortality
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Long-term sequelae include neurodevelopmental
deficits and increased risk of chronic disease in
adulthood
Preterm birth costs the health care system
$26 billion annually
Preterm Birth: Significance
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The risk of morbidity
and mortality
decrease as
gestational age
increases, but the
relationship is nonlinear
The point with the
lowest risk is between
39 0/7 and 40 6/7
weeks
Prediction
Preterm Birth: Risk Factors
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Prior preterm birth
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The number one risk factor for preterm birth
The more preterm births, the stronger the risk of
recurrence:
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One prior preterm birth: 14-22%
Two prior preterm births: 28-42%
More than 3 prior preterm births: 67%
Most recurrent preterm births occur within 2
weeks of the gestational age of the prior preterm
birth
Preterm Birth: Risk Factors
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Cervical and Uterine Factors
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Short cervix
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Cervical surgery
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There is an inverse relationship between cervical length by
ultrasound and gestational age at delivery
More to come on this later….
Ablative and excisional procedures for treatment of cervical
intraepithelial neoplasia have been associate with increased
risk of preterm birth
Uterine malformations
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Congenital and acquired malformations are associated with
preterm birth
Preterm Birth: Risk Factors
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Lifestyle factors
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Smoking, Substance abuse
Body mass index
Physical activity, work, and stress
Demographic factors
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Race
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African Americans are at the highest risk for preterm
birth
Socioeconomic status
Educational status
Preterm Birth: Risk Factors
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Infection
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Bacterial vaginosis and other vaginal infections
Asymptomatic bacteruria
Peridontal disease
Multiple gestation
Birth defects
Threatened abortion
Inter-pregnancy interval
Genetic factors
Preterm Birth: Screening
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Transvaginal cervical
ultrasonography
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An increased risk of PTB as
cervical length shortens has
been observed in all
populations
Cervical length below the
10th percentile (25 mm) is
consistently associated with
an increased risk of PTB
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90th percentile: 45 mm
50th percentile: 35 mm
10th percentile: 25 mm
5th percentile: 20 mm
2nd percentile: 15 mm
Preterm Birth: Screening
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Cervical length screening by history
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High risk population: Prior preterm birth < 34
weeks
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Transvaginal ultrasound for cervical length every 2
weeks from 16 to 24 weeks
Low risk population: No history of preterm birth
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One time transabdominal screening at anatomy
ultrasound (usually ~18 weeks) with transvaginal
ultrasound only if first measurement concerning
Preterm Birth: Screening
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Fetal Fibronectin
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A basement membrane protein produced by the fetal
membranes
Thought to act as an adhesion molecule that binds the
placenta and membranes to the uterine decidua
Rarely found in the vagina after 20 weeks gestation in a
normal pregnancy
When found in the vagina after 20 weeks, it has been
associated with an increased risk of spontaneous PTB
Low sensitivity, high specificity
ACOG no longer recommends its use as a screening tool
Preterm Birth: Screening
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Home uterine activity monitoring
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Not recommended
Bacterial vaginosis screening
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Not recommended
Prevention
Preterm Birth: Prevention
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History
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17α-hydroxyprogesterone caproate injections
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Any woman with a singleton gestation and prior
spontaneous preterm delivery should receive weekly
progesterone injections from 16 to 36 weeks
Use of progesterone in these high risk patients has
been shown to significantly reduce the risk of recurrent
preterm birth
This is thought to reduce inflammation, maintain
cervical integrity, and antagonize oxytocin
Preterm Birth: Prevention
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Cervical length
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High risk patients
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Cerclage
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If cervical length < 25 mm prior to 24 weeks
Associated with a 30% reduction in preterm birth along with
decreased perinatal morbidity and mortality
Low risk patients
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Vaginal progesterone
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If cervical length is < 20 mm prior to 24 weeks
Associated with ~ 45% reduction in preterm birth
Cerclage
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Has not been shown to significantly reduce preterm birth
rate, even at cervical lengths < 15 mm
Management
Preterm Birth: Symptoms
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Cramping
Contractions
Low back pain
Lower abdominal pressure
Vaginal discharge
Preterm Birth: Diagnosis
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It’s not preterm labor without cervical change
Contractions alone without cervical change
carry a 40-70% false-positive rate
Fetal fibronectin
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The value is in its negative predictive value
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>99% for delivery within 14 days
Positive predictive value
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Only 13-33% (!) for delivery in 7-10 days
Preterm Birth: Intervention
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Tocolytics
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The goal of tocolysis is for short-term prolongation of
pregnancy to allow administration of antenatal
steroids a well as maternal transport if needed
No evidence exists that tocolytic therapy has any
direct favorable effect on neonatal outcomes
Long-term use of any of these agents carries a high
risk for side effects– both maternal and fetal
A few examples: Magnesium sulfate, Calcium channel
blockers (Nifedipine), NSAIDs (Indomethacin), Betaadrenergic receptor antagonists (Terbutaline)
Preterm Birth: Intervention
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Antenatal corticosteroids
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This is the single most beneficial intervention for
improved neonatal outcomes in patients who deliver
preterm
Neonates whose mothers receive steroids have
significantly lower severity and frequency of
respiratory distress syndrome, intracranial
hemorrhage, necrotizing enterocolitis, and death
(compared to those who do not receive steroids)
Betamethasone and Dexamethasone are the most
widely studied corticosteroids and are equivalent in
efficacy
Preterm Birth: Intervention
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Antenatal corticosteroids
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A single course of steroids is recommended for any
woman at risk for preterm delivery between 24 and 34
weeks
A single rescue course at least 2 weeks after the first
course has additional neonatal benefit
However, regularly scheduled repeat courses are not
recommended
Preterm Birth: Intervention
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Antibiotics
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It has been theorized that infection or
inflammation are associated with contractions
However, it has never been shown that antibiotic
treatment in women with preterm labor and intact
membranes have any benefit in prolonging the
pregnancy
This is different than the important antibiotic
prophylaxis for GBS prophylaxis and in the setting
of rupture of membranes
Preterm Birth: Intervention
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Neuroprotection
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Pre-delivery administration of magnesium sulfate
reduces the occurrence of cerebral palsy
Magnesium sulfate should be given with the intent
for neuroprotection when birth is anticipated prior
to 32 weeks
Same protocol essentially as magnesium for
tocolysis and preeclampsia seizure prophylaxis
Multiples
Preterm Birth: Multiples
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In 2006, 60% of twins and 93% of triplets were
born preterm
Unfortunately, many of the strategies listed
previously are ineffective or actually detrimental
in a multi-fetal pregnancy
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Progesterone treatment does not reduce the
incidence of preterm birth
Cerclage may actually increase the risk of preterm
birth– not recommended
Tocolytics carry a much higher risk of side effects in
this population
Preterm Birth: Multiples
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There is not even adequate data to
demonstrate benefit from the use of antenatal
steroids in multiple gestations
However, because of the clear benefit
attributable to corticosteroids in singleton
gestations, steroids are readily utilized in
multiple gestations
The same concept applies to magnesium
sulfate for neuroprotection
Conclusions
Preterm Birth: Conclusions
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Preterm birth remains a common
complication for many women in the United
States
It carries a huge financial burden for families
affected as well as the health care system as
a whole
There are multiple risk factors for preterm
birth, but a prior history of this event is the
strongest predictor of recurrence
Preterm Birth: Conclusions
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There are few reliable methods of prediction
available– maternal history and cervical
length
There are even fewer reliable methods of
prevention once an increased risk of preterm
delivery is identified– progesterone and
cerclage
Preterm labor can be elusive at times
Preterm Birth: Conclusions
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Once preterm labor is diagnosed, several
treatments are available to reduce the
neonatal morbidity and mortality if preterm
birth occurs– antenatal steroids and
magnesium sulfate
Multifetal gestations have a very high risk of
preterm birth, but unfortunately, effective
prevention and management options are
limited in this setting
Questions?
Thank you!
References
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Prediction and prevention of preterm birth. ACOG Practice Bulletin Number 130, October
2012.
Cunningham FG, Leveno KJ, Bloom SL, et al. Williams Obstetrics. 23 rd edition. McGraw
Hill. 2010.
Goldenberg RL, Mercer BM, Meis PJ., et al. The preterm prevention study: fetal fibronectin
testing and spontaneous preterm birth. Obstet Gynecol. 1996;87:643-48.
Goldenberg RL, Iams JD, Das A., et al. The preterm prevention study: sequential cervical
length and fetal fibronectin testing for the prediction of spontaneous preterm birth. Am J
Obstet Gynecol 2000;182:636-43.
Iams JD, Geldenberg RL, Meis PJ, et al. The length of the cervix and the risk of
spontaneous premature delivery. NEJM 1996;334:567-72.
Lockwood CJ, Senyei AE, Dische MR, et al. Fetal fibronectin in cervical and vaginal
secretions as a predictor of preterm delivery. NEJM 1991;325:669-74.
To MS, Alfirevic Z, Heath VC, et al. Cervical cerclage for prevention of preterm delivery in
women with short cervix: a randomised controlled trial. Lancet 2004;363:1849-53.
Goya M, Pratcorona L, Merced c, et al. Cervical pessary in pregnant women with a short
cervix (PECEP): an open label randomised controlled trial. Lancet 2012;379:1800-6.
Rouse DJ, Caritis SN, Peaceman aM, et al. A trial of 17 alpha-hydroxyprogesterone
caproate to prevent prematurity in twins. NEJM 2007:357:454-61.