The epidemiology of preterm labor

doi:10.1053/sper.2001.27548

Seminars in Perinatology

Volume 25, Issue 4, August 2001, Pages 204-214

https://doi.org/10.1053/sper.2001.27548 Get rights and content

There are many factors that are associated with preterm labor and delivery. These include maternal conditions such as medical illness, anemia and uterine malformation. They may be related to past events such as prior obstetric complication, previous preterm labor, cervical surgery or induced abortion. They may be intrinsic to the current pregnancy, such as reproductive tract infection, multifetal gestation, maternal age, short interpregnancy interval or prolonged menstrual conception interval. Maternal behaviors such as smoking and substance abuse can be risk factors for a short gestation. Demographic variables such as race, employment and socioeconomic status can also be associated with preterm labor. This article briefly reviews these subjects.

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Placental extracellular vesicles–associated microRNA-519c mediates endotoxin adaptation in pregnancy
2021, American Journal of Obstetrics and Gynecology
Citation Excerpt :
This is a possible defense mechanism to limit infection-induced immune responses in many diseases and possibly during pregnancy.34–36 In fact, although many pregnant women are exposed to repeated infections,11,34,37–41 only 2% to 4% of them have infection-induced preterm deliveries.39,42,43 This indicates that the gestational tissues in normal pregnancies are capable of clearing nonsevere infections without inducing exaggerated inflammatory responses that might threaten the antiinflammatory and propregnancy environment.
Pregnancy represents a unique challenge for the maternal-fetal immune interface, requiring a balance between immunosuppression, which is essential for the maintenance of a semiallogeneic fetus, and proinflammatory host defense to protect the maternal-fetal interface from invading organisms. Adaptation to repeated inflammatory stimuli (endotoxin tolerance) may be critical in preventing inflammation-induced preterm birth caused by exaggerated maternal inflammatory responses to mild or moderate infections that are common during pregnancy. However, the exact mechanisms contributing to the maintenance of tolerance to repeated infections are not completely understood. MicroRNAs play important roles in pregnancy with several microRNAs implicated in gestational tissue function and in pathologic pregnancy conditions. MicroRNA-519c, a member of the chromosome 19 microRNA cluster, is a human-specific microRNA mainly expressed in the placenta. However, its role in pregnancy is largely unknown.
This study aimed to explore the role of “endotoxin tolerance” failure in the pathogenesis of an exaggerated inflammatory response often seen in inflammation-mediated preterm birth. In this study, we investigated the role of microRNA-519c, a placenta-specific microRNA, as a key regulator of endotoxin tolerance at the maternal-fetal interface.
Using a placental explant culture system, samples from term and second-trimester placentas were treated with lipopolysaccharide. After 24 hours, the conditioned media were collected for analysis, and the placental explants were re-exposed to repeated doses of lipopolysaccharide for 3 days. The supernatant was analyzed for inflammatory markers, the presence of extracellular vesicles, and microRNAs. To study the possible mechanism of action of the microRNAs, we evaluated the phosphodiesterase 3B pathway involved in tumor necrosis factor alpha production using a microRNA mimic and phosphodiesterase 3B small interfering RNA transfection. Finally, we analyzed human placental samples from different gestational ages and from women affected by inflammation-associated pregnancies.
Our data showed that repeated exposure of the human placenta to endotoxin challenges induced a tolerant phenotype characterized by decreased tumor necrosis factor alpha and up-regulated interleukin-10 levels. This reaction was mediated by the placenta-specific microRNA-519c packaged within placental extracellular vesicles. Lipopolysaccharide treatment increased the extracellular vesicles that were positive for the exosome tetraspanin markers, namely CD9, CD63, and CD81, and secreted primarily by trophoblasts. Primary human trophoblast cells transfected with a microRNA-519c mimic decreased phosphodiesterase 3B, whereas a lack of phosphodiesterase 3B, achieved by small interfering RNA transfection, led to decreased tumor necrosis factor alpha production. These data support the hypothesis that the anti-inflammatory action of microRNA-519c was mediated by a down-regulation of the phosphodiesterase 3B pathway, leading to inhibition of tumor necrosis factor alpha production. Furthermore, human placentas from normal and inflammation-associated pregnancies demonstrated that a decreased placental microRNA-519c level was linked to infection-induced inflammatory pathologies during pregnancy.
We identified microRNA-519c, a human placenta-specific microRNA, as a novel regulator of immune adaptation associated with infection-induced preterm birth at the maternal-fetal interface. Our study serves as a basis for future experiments to explore the potential use of microRNA-519c as a biomarker for infection-induced preterm birth.
Exposure to life-threatening stressful situations and the risk of preterm birth and low birth weight
2014, International Journal of Gynecology and Obstetrics
Citation Excerpt :
Data were not available for history of previous PTB, maternal body mass index, and smoking habits. These characteristics are known to influence the risks of PTB and LBW [24]. A history of PTB, for instance, increases the risk for PTB in subsequent pregnancies.
To evaluate the association between exposure to life-threatening rocket attacks and the risks of preterm birth (PTB) and low birth weight (LBW).
The present retrospective cohort study compared the outcomes of 1851 births by women exposed to rocket attacks and 2979 births by unexposed women. The timing, frequency, and intensity of exposure were calculated for each trimester and for the entire pregnancy period. Demographic and medical data were abstracted from the patients’ records.
The rates of PTB and LBW were higher among exposed than unexposed women (PTB: 9.1% versus 6.8%, P = 0.004; LBW: 7.6% versus 5.8%, P = 0.02). The rate of infants who were small for gestational age did not differ between the groups. After controlling for potential confounders, the risks for PTB and LBW remained significantly higher in the exposed group (PTB: adjusted odds ratio 1.3 [95% confidence interval, 1.1–1.7]; LBW: adjusted odds ratio 1.3 [95% confidence interval, 1.03–1.7]). There was no linear association between the intensity of exposure and the risk of PTB or LBW.
Maternal exposure to intermittent but repeated life-threatening rocket attacks for a prolonged period might be associated with increased risks of PTB and LBW.
Prevention of preterm birth
2012, Seminars in Fetal and Neonatal Medicine
Citation Excerpt :
Secondary prevention efforts are directed at women who are already at higher risk of preterm birth. The most significant and consistently identified risk factor for preterm birth is a woman’s history of previous preterm birth.40–48 Estimates suggest that the rate of recurrent preterm birth in this group of women is 20–25%,49 a 2.5-fold increased relative risk when compared to women with no previous spontaneous preterm birth.50
Preterm birth (delivery before 37 completed weeks of gestation) is common and rates are increasing. In the past, medical efforts focused on ameliorating the consequences of prematurity rather than preventing its occurrence. This approach resulted in improved neonatal outcomes, but it remains costly in terms of both the suffering of infants and their families and the economic burden on society. Increased understanding of the pathophysiology of preterm labor has altered the approach to this problem, with increased focus on preventive strategies. Primary prevention is a limited strategy which involves public education, smoking cessation, improved nutritional status and avoidance of late preterm births. Secondary prevention focuses on recurrent preterm birth which is the most recognisable risk factor. Widely accepted strategies include cervical cerclage, progesterone and dedicated clinics. However, more research is needed to explore the role of antibiotics and anti-inflammatory treatments in the prevention of this complex problem.
Multiple Gestations and Assisted Reproductive Technology
2012, Avery's Diseases of the Newborn (Ninth Edition)
Multiple gestations and assisted reproductive technology
2011, Avery's Diseases of the Newborn
The role of prenatal care in recurrent preterm birth
2011, European Journal of Obstetrics and Gynecology and Reproductive Biology
Citation Excerpt :
Rising rates of preterm delivery worldwide and the failure of prevention programs are a growing concern in contemporary obstetrics [1–3] as preterm delivery continues to be a major risk factor for neonatal morbidity and mortality [3–8].
To assess the independent role of prenatal care in preventing recurrent preterm delivery (<37 weeks gestation) and in reducing adverse pregnancy outcomes in recurrent preterm delivery.
A population-based retrospective cohort study. Participants were 1470 Bedouin women in Southern Israel who at their first delivery (parity 1) gave birth preterm (<37 weeks) and had a consecutive birth (parity 2) at Soroka University Medical Center, the only birth hospital in the area. Multiple gestations were excluded.
The incidence of recurrent preterm delivery was 24.6% (362/1470) and it was not associated with having had prenatal care in the second pregnancy. In a multivariable logistic analysis, young maternal age, pregnancy complications and fetal abnormalities in the second pregnancy, as well as previous miscarriages, short inter-pregnancy interval, and length of gestation in the first pregnancy were significantly associated with recurrence. The incidence of adverse pregnancy outcomes (perinatal mortality, small for gestational age, gestational age < 34 weeks, Apgar ≤ 7) in recurrent preterm delivery was 44.8% (162/362). Lack of prenatal care was significantly associated with adverse pregnancy outcomes (odds ratio: 4.03; 95% confidence interval: 2.04–7.97) in a multivariable logistic analysis controlling for all variables significantly associated with adverse pregnancy outcomes at the univariate analysis.
Prenatal care may reduce the risk of adverse pregnancy outcomes in recurrent preterm delivery, even if recurrence cannot be prevented. It is therefore important that quality prenatal care is accessible to women who had a preterm delivery in the past.

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The epidemiology of preterm labor

Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Obstet Gynecol

Obstet Gynecol

Eur J Obstet Gynecol Reprod Biol

Fertil Steril

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

J Clin Epidemiol

Am J Obstet Gynecol

Am J Obstet Gynecol

Public Health

Am J Obstet Gynecol

Ann Epidemiol

Obstet Gynecol

Prevention of preterm births: A perinatal study in Haguenau, France

Pediatrics

Did preterm birth in France continue to decrease in the 1980s?

Paediatr Perinat Epidemiol

Epidemiology of preterm birth in two birth cohorts with an interval of 20 years

Am J Epidemiol

Increasing evidence of low birth weight-United States 1981–91

MMWR Morb Mortal Wkly Rep

The problem of low birth weight

Future Child

Recent trends in infant mortality rates and proportion of low birth weight live births in Canada

CMAJ

Secular trends in preterm birth. A hospital-based study

JAMA

Prevention of premature births

JAMA

The preterm prediction study: effect of gestational age and cause of preterm birth on subsequent outcome. National Institute of Child health and Human Development Maternal-Fetal Medicine Units Network

Am J Obstet Gynecol

Rates and factors associated with recurrence of preterm delivery

JAMA

Early pregnancy predictors of preterm birth: the role of a prolonged menstruationconception interval

BJOG

Causespecific trends in neonatal mortality among black and white infants, United States, 1980–1995

Matern Child Health J

Births: Final data for 1998

Natl Vital Stat Rep

Is race a risk factor or a risk marker for preterm delivery?

Ethn Dis

Racial differences in the patterns of singleton preterm delivery in the 1988 National Maternal and Infant Health Survey

Matern Child Health J

The risk of recurrence of premature births to African-American and white women

J Assoc Acad Minor Phys

Current Concepts. The control of labor

N Engl J Med

Pathology of the Placenta, Membranes, and Umbilical Cord in Bacterial, Fungal, and Viral Infections in Man

Monogr Pathol

Acute Bacterial Chorioamnionitis

Prog Clin Biol Res

Prematurity and perinatal mortality in pregnancies complicated by maternal Chlamydia Trachomatis infections

JAMA

Association between bacterial vaginosis and preterm delivery of a low-birth weight infant

N Engl J Med

Gonorrhea in Pregnancy

Am J Obstct Gynecol

Ureaplasma urealyticum and Premature Birth

Clin Infect Dis

A Randomized Placebo-Controlled Trial of Erythromycin for the Treatment of Ureaplasma urealyticum to Prevent Premature Delivery

Am J Obstet Gynecol

Association Between a Shift in Vaginal Flora on Papanicolaou Smear and Acute Chorioamnionitis and Preterm Delivery

Diagn Cytopathol

Comparison of Polymerase Chain Reaction Assay with Culture for Detection of Genital Mycoplasmas in Perinatal Infections

Eur J Clin Microbiol Infect Dis

Microbiological synthesis and transformation of prostaglandins

Prikl Biokhim Mikrobiol

Screening for Bacterial Vaginosis

Infect Dis Obstet Gynecol

Premature Labor. II. Bacterial Sources of Phospholipase

Obstet Gynecol

Health and demographic characteristics of twin births: United States, 1988. National Center for Health Statistics