Preterm Birth

Birth of a child before 37 weeks of pregnancy

Illustration of hands reaching out for swaddled baby in incubator representing preterm birth
Two bobs of different colors

Preterm birth does not always have long term consequences, but it is important to know what might increase your chances so that you can be proactive in monitoring your pregnancy

What is preterm birth?

The average pregnancy has a 40-week gestational period. If a live birth occurs before the 37th week, it is considered to be preterm or premature. Since the brain, lungs and liver are still developing in the final weeks of pregnancy, preterm babies and especially those born before 32 weeks are at a higher risk of complications such as difficulties breathing, disabilities, or even death [1]. Generally speaking, the more premature the birth, the higher risk there is for the child and the mother.

How common is it?

Around 10% of all births are preterm [2]. However, not all premature babies have negative outcomes. The majority of preterm births will only be 1 to 2 weeks premature, meaning that the chances of either the mother or child experiencing any long-term health risks is fairly low.

How is preterm birth linked with the vaginal microbiome?

Many of the causes of premature births are not well understood. Some of the documented risk factors for delivering a baby before 37 weeks include having had a premature birth for a previous pregnancy, conceiving through IVF, being a teenager or over the age of 35, genetic or chronic conditions, and behavioral factors such as smoking, drug use and high stress-levels [2]. 

In addition, we do know that conditions of the vaginal and endometrial microbiome also correlate with an increased risk of preterm birth. These include bacterial vaginosis, aerobic vaginitis, yeast infections, trichomoniasis, mycoplasma and ureaplasma infections [3, 4, 5]. Some of these conditions can lead to chorion (chorionamnionitis) or decidua (deciduitis) infections which directly trigger preterm birth [6]. However, chorioamnionitis and deciduitis can also arise independently and without explanation. 

What are the diagnostic and treatment options for preterm birth?

During pregnancy, it is important to talk to your doctor about your medical history and relevant risk factors. If they think you might be at a high risk for preterm birth, they can perform a pelvic exam, uterine monitoring, an ultrasound, or conduct lab tests to confirm [7].

To reduce the risk of preterm birth associated with the vaginal microbiome, it is important to identify and treat any underlying conditions where possible. For example, antibiotics can be used to treat most STDs and antifungal medications can be prescribed for yeast infections [7].

While it is not possible to stop the delivery once the mother’s water has broken, the process can be slowed down. Therefore, it is important to seek medical attention as soon as possible to evaluate the best available options and to avoid further complications [7]. 

What can prevent preterm birth?

In order to determine what steps you can take to prevent preterm birth, it is important to discuss any potential risk factors including previous preterm births with your doctor so that they can help monitor you throughout your pregnancy. If you have experienced a preterm birth before, your doctor might prescribe progesterone [7]. 

In addition to diagnosing and treating any underlying vaginal conditions as early as possible in your pregnancy, you can help ward off infections by maintaining the balance of protective bacteria in the vaginal microbiome. To avoid disrupting that balance, limit the use of douches as well as scented soaps, tampons or pads. To reduce your chances of getting an STI, practice safe sex by always discussing sexual health with your partner, using barrier protection correctly (such as a condom or dental dam), and getting tested regularly. 

Where can I get more information about preterm birth?

While your healthcare can help guide you in navigating the complexities around preterm birth, the CDC also offers additional information.

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1. Public Health Strategies to Prevent Preterm Birth [Internet]. Centers for Disease Control and Prevention. 2020 [cited 7 September 2020]. Available from: 

2. Preterm Birth | Maternal and Infant Health | Reproductive Health | CDC [Internet]. 2020 [cited 7 September 2020]. Available from:

3. Donders G, Van Calsteren K, Bellen G, Reybrouck R, Van den Bosch T, Riphagen I et al. Predictive value for preterm birth of abnormal vaginal flora, bacterial vaginosis and aerobic vaginitis during the first trimester of pregnancy. BJOG: An International Journal of Obstetrics & Gynaecology. 2009;116(10):1315-1324.

4. Farr A, Kiss H, Holzer I, Husslein P, Hagmann M, Petricevic L. Effect of asymptomatic vaginal colonization with Candida albicanson pregnancy outcome. Acta Obstetricia et Gynecologica Scandinavica. 2015;94(9):989-996.

5. Miyoshi Y, Suga S, Sugimi S, Kurata N, Yamashita H, Yasuhi I. Vaginal Ureaplasma urealyticum or Mycoplasma hominis and preterm delivery in women with threatened preterm labor. The Journal of Maternal-Fetal & Neonatal Medicine. 2020;1-6.

6. Hočevar K, Maver A, Vidmar Šimic M, Hodžić A, Haslberger A, Premru Seršen T et al. Vaginal Microbiome Signature Is Associated With Spontaneous Preterm Delivery. Frontiers in Medicine. 2019;6.

7. Preterm labor - Symptoms and causes [Internet]. Mayo Clinic. 2020 [cited 7 September 2020]. Available from:

Written by Aisha Ommaya, science comms officer with Juno Bio

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