Infection and preterm labor

Infection can impact a pregnancy in two major ways, both with serious effects.

• After premature rupture of membranes (PROM), both a mother and her fetus are at risk of developing an infection, which can cause serious illness, disability, or death. For preterm PROM (pPROM):¹
  • Antibiotics are given in an attempt to prevent infection and prolong the pregnancy.
  • Before 34 weeks of pregnancy, antenatal corticosteroids are given to the mother to help develop the fetus's lungs.
• Bacterial infection that spreads to the uterus and amniotic fluid is a major cause of preterm labor.² (Viral infection is rarely involved in preterm labor.³) Uterine infection triggers the release of substances that make the uterus contract and can cause the amniotic sac to rupture (PROM). Either or both of these events will start preterm labor. Infection can begin:
  • In the vagina, such as bacterial vaginosis (BV), often without symptoms. Studies show that in most cases of preterm labor caused by infection, the bacteria found in the uterus came from the vagina.³
  • In the urinary tract. A urinary tract infection can lead to serious kidney infection and endanger both a mother and her fetus.
  • After amniocentesis or cervical cerclage is performed (this is very rare).¹
  • Through the mother's bloodstream (this is rare).³

Antibiotic treatment of infection and preterm labor

Antibiotics are recommended for specific problems in pregnancy, some of which may cause preterm labor.

• Urinary tract infection (UTI). All women are screened for UTI at their first prenatal visit. Antibiotic treatment is recommended for UTI, regardless of whether a pregnant woman has symptoms.
• Bacterial vaginosis (BV). Bacterial vaginosis is usually diagnosed when it causes symptoms, usually a bad-smelling vaginal discharge. Antibiotic medication can be used to correct an overgrowth of problem bacteria in the vagina. BV infection during pregnancy has been linked to a higher risk of preterm birth. Although treatment doesn't seem to prevent preterm birth, it does lower your baby's risk of low birth weight and your risk of premature rupture of membranes.⁴ Your doctor or nurse-midwife will use antibiotics for BV if you have symptoms.
• Preterm labor with pPROM. Antibiotic treatment is recommended for women with pPROM, as it prolongs pregnancy and reduces the risk of maternal and newborn infection.¹
• Preterm labor without pPROM. Antibiotics do not seem to stop preterm labor or prevent complications in women with preterm labor, intact membranes, and no evidence of infection.⁵
• Group B streptococcus infection. Group B strep are a type of bacteria that can cause a severe infection in newborns. Women with PROM are screened for group B strep, as are all women at 36 weeks of pregnancy. If a mother tests positive, she is treated with antibiotics during labor in an attempt to prevent infection in her newborn.

Citations

1. American Academy of Pediatrics and American College of Obstetricians and Gynecologists (2002). Obstetric and medical complications. In Guidelines for Perinatal Care, 5th ed., pp. 163–185. Washington, DC: American Academy of Pediatrics, American College of Obstetricians and Gynecologists.

2. Goldenberg RL, Rouse DJ (1998). Prevention of premature birth. New England Journal of Medicine, 339(5): 313–320.

3. Goldenberg RL, et al. (2000). Intrauterine infection and preterm delivery. New England Journal of Medicine, 342(20): 1500–1507.

4. McDonald H, et al. (2006). Antibiotics for treating bacterial vaginosis in pregnancy. Cochrane Database of Systematic Reviews (1). Oxford: Update Software.

5. American College of Obstetricians and Gynecologists (2003). Management of preterm labor. ACOG Practice Bulletin No. 43. Obstetrics and Gynecology, 101(5): 1039–1047.