What are the risk factors for preterm labor?

Answer

The exact mechanism(s) of preterm labor is largely unknown but is believed to include decidual hemorrhage, (eg, abruption, mechanical factors such as uterine overdistension from multiple gestation or polyhydramnios), cervical incompetence (eg, trauma, cone biopsy), uterine distortion (eg, müllerian duct abnormalities, fibroid uterus), cervical inflammation (eg, resulting from bacterial vaginosis [BV], trichomonas), maternal inflammation/fever (eg, urinary tract infection), hormonal changes (eg, mediated by maternal or fetal stress), and uteroplacental insufficiency (eg, hypertension, insulin-dependent diabetes, drug abuse, smoking, alcohol consumption).^{[2, 3]} A genomewide association study that included 43,568 European women identified six genes (BF1, EEFSEC, AGTR2, WNT4, ADCY5, and RAP2C) that were associated with gestational duration, of which, three genes were associated with preterm birth (EBF1, EEFSEC, and AGTR2).^[6]

Although prediction of preterm delivery remains inexact, a variety of maternal and obstetric characteristics are known to increase the risk, presumably via one of these mechanisms. Finally, the fetus plays a role in the initiation of labor. In a simplistic sense, the fetus recognizes a hostile intrauterine environment and precipitates labor by premature activation of a fetal-placental parturition pathway.

Risk factors for preterm birth include demographic characteristics, behavioral factors, and aspects of obstetric history such as previous preterm birth. Demographic factors for preterm labor include nonwhite race, extremes of maternal age (< 17 y or >35 y), low socioeconomic status, and low prepregnancy weight. Preterm labor and birth can be associated with stressful life situations (eg, domestic violence; close family death; insecurity over food, home, or partner; work and home environment) either indirectly by associated risk behaviors or directly by mechanisms not completely understood. Many risk factors may manifest in the same gravida.

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Algorithm for use of progestogens in prevention of PTB in clinical care. aIf TVU CL screening is performed; b17P 250 mg intramuscularly every week from 16-20 weeks to 36 weeks; ceg, daily 200-mg suppository or 90-mg gel from time of diagnosis of short CL to 36 weeks. CL, cervical length; PTB, preterm birth; 17P, 17-alpha-hydroxy-progesterone caproate; TVT, transvaginal ultrasound. Reprinted from Society for Maternal-Fetal Medicine Publications Committee, with assistance of Vincenzo Berghella. Progesterone and preterm birth prevention: translating clinical trials data into clinical practice. Am J Obstet Gynecol. 2012 May; 206(5):376-86, with permission from Elsevier.

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Author

Michael G Ross, MD, MPH Distinguished Professor of Obstetrics and Gynecology, University of California, Los Angeles, David Geffen School of Medicine; Distinguished Professor, Department of Community Health Sciences, Fielding School of Public Health at University of California at Los Angeles

Michael G Ross, MD, MPH is a member of the following medical societies: American Association for the Advancement of Science, American College of Obstetricians and Gynecologists, American Federation for Clinical Research, American Gynecological and Obstetrical Society, American Physiological Society, American Public Health Association, Association of Professors of Gynecology and Obstetrics, Perinatal Research Society, Phi Beta Kappa, Society for Maternal-Fetal Medicine, Society for Neuroscience, Society for Reproductive Investigation

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Richard S Legro, MD Professor, Department of Obstetrics and Gynecology, Division of Reproductive Endocrinology, Pennsylvania State University College of Medicine; Consulting Staff, Milton S Hershey Medical Center

Richard S Legro, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, Society of Reproductive Surgeons, American Society for Reproductive Medicine, Endocrine Society, Phi Beta Kappa

Disclosure: Received honoraria from Korea National Institute of Health and National Institute of Health (Bethesda, MD) for speaking and teaching; Received honoraria from Greater Toronto Area Reproductive Medicine Society (Toronto, ON, CA) for speaking and teaching; Received honoraria from American College of Obstetrics and Gynecologists (Washington, DC) for speaking and teaching; Received honoraria from National Institute of Child Health and Human Development Pediatric and Adolescent Gynecology Research Thi.

Chief Editor

Carl V Smith, MD The Distinguished Chris J and Marie A Olson Chair of Obstetrics and Gynecology, Professor, Department of Obstetrics and Gynecology, Senior Associate Dean for Clinical Affairs, University of Nebraska Medical Center

Carl V Smith, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, Association of Professors of Gynecology and Obstetrics, Central Association of Obstetricians and Gynecologists, Society for Maternal-Fetal Medicine, Council of University Chairs of Obstetrics and Gynecology, Nebraska Medical Association

Disclosure: Nothing to disclose.

Additional Contributors

Suzanne R Trupin, MD, FACOG Clinical Professor, Department of Obstetrics and Gynecology, University of Illinois College of Medicine at Urbana-Champaign; CEO and Owner, Women's Health Practice; CEO and Owner, Hada Cosmetic Medicine and Midwest Surgical Center

Suzanne R Trupin, MD, FACOG is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, International Society for Clinical Densitometry, AAGL, North American Menopause Society, American Medical Association, Association of Reproductive Health Professionals

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author, Dr. Edward Newton, MD, to the development and writing of this article.

The authors and editors of Medscape Reference also gratefully acknowledge the contributions of previous coauthor, Dr. Robert D Eden, MD, to the development and writing of this article.

What are the risk factors for preterm labor?

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