Review
Obstetrics
Care for women with prior preterm birth

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Women who have delivered an infant between 16 and 36 weeks' gestation have an increased risk of preterm birth in subsequent pregnancies. The risk increases with more than 1 preterm birth and is inversely proportional to the gestational age of the previous preterm birth. African American women have rates of recurrent preterm birth that are nearly twice that of women of other backgrounds. An approximate risk of recurrent preterm birth can be estimated by a comprehensive reproductive history, with emphasis on maternal race, the number and gestational age of prior births, and the sequence of events preceding the index preterm birth. Interventions including smoking cessation, eradication of asymptomatic bacteriuria, progestational agents, and cervical cerclage can reduce the risk of recurrent preterm birth when employed appropriately.

Section snippets

The contribution of prior preterm birth to preterm birth in general

Approximately 13 million of the more than 130 million babies born annually worldwide are born preterm, a global incidence of nearly 10%.29 There are more than 500,000 births before 37 weeks' gestation in the United States each year, a rate of 12.7% in 2007.30 Of these, about 15% occur in women with a prior preterm birth.31 Current effective interventions could potentially eliminate as many as 35-50% of recurrent preterm births (n ∼ 37,000).

Identification of women with a prior preterm birth

A thorough obstetrical history is essential to identify women with prior preterm birth. Unfortunately, the nomenclature used to describe pregnancy outcomes, expressed as gravidity, parity (births after 20 menstrual weeks' gestation), and abortions (births before 20 weeks'), lacks a “clear epidemiologic, biologic, or clinical basis”26 and is inconsistent with recent obstetrical epidemiology: Women whose prior pregnancy ended between 16 and 20 weeks have a risk of recurrent preterm birth that

Document the clinical presentation of the prior preterm birth(s)

Preterm parturition is characterized by cervical ripening, decidual-membrane activation, and uterine contractions, any of which may predominate. The order in which these steps occurred can often be discerned from the history, offering clues to the etiology that can improve the prediction of recurrence risk. Obstetricians have traditionally been taught to ask about painful contractions as evidence that true labor has begun at term, but focusing on the presence and pain of contractions is

Recurrent vs nonrecurrent preterm birth

Women with recurrent preterm birth are more likely to have a low prepregnancy weight (below 100 pounds, with a body mass index <19.8 kg/m2) and to be African American than women with a single prior preterm birth.46, 47, 48, 49, 50, 51 The risk of recurrent preterm birth increases as the gestational age of the previous preterm birth declines and as the number of previous preterm births increases, and thus is highest in women with more than 1 early preterm birth.52 Women with more than 1 preterm

Estimation of individual risk of recurrent preterm birth

The risk of recurrent preterm birth is commonly reported to be increased by 1.5- to 2-fold to 4-fold or more, depending on the population. The risk increases with the number of prior preterm births and as the gestational age decreases (Figure 2 from McManemy et al52).

There are 3 historical factors that have a substantial influence on the likelihood of recurrent preterm birth. All are immediately available without cost: maternal race (African American vs all others), the gestational age of the

Interventions to reduce the risk of recurrent preterm birth

Numerous strategies and treatments have been proposed to reduce the risk of recurrent preterm birth, but few have been found effective when tested in clinical trials. The interventions in the following text are grouped according to the strength of evidence supporting their use:

Interventions supported by firm evidence

  • Smoking-cessation programs: pregnant women are uniquely receptive to smoking-cessation programs, especially when physicians participate directly and repeatedly. Smoking-cessation programs in pregnancy have been reported to reduce the rate of preterm birth by 16% (relative risk, 0.84; 95% confidence interval [CI], 0.72–0.9862) to 31% (adjusted odds ratio [aOR], 0.69; 95% CI, 0.65–0.74).63

  • Screening and treatment for asymptomatic bacteriuria: screening for asymptomatic bacteriuria reduces

Interventions suggested to reduce the risk of recurrent preterm birth for which evidence is absent, minimal, or mixed

  • Surveillance of cervical length with transvaginal ultrasound has never been compared to digital or no cervical examination in a randomized trial of women with a prior preterm birth. Cervical ultrasound can reveal and quantify changes in the cervix sooner and more reproducibly than digital examination.77, 78 However, the effect of cervical sonography on outcomes has not been demonstrated, and experience with ambulatory uterine contraction monitoring has shown that more information does not

Interventions that have been shown to be ineffective to reduce the risk of recurrent preterm birth

  • Nutritional supplements: randomized, placebo-controlled trials of vitamins C and E have not found any reduction in preterm birth.101, 102

  • Early detection of preterm labor (PTL): small early trials suggested benefit, but subsequent randomized trials of programs to detect PTL, including provider-initiated care, frequent nurse contact, and outpatient home uterine contraction monitoring, did not reveal reduction of recurrent preterm birth.7

  • Contraction suppression: contraction suppression with

The context of prenatal care for women with a prior PTB

Women with a prior PTB may have lower rates of recurrent PTB when prenatal care includes specific attention to open communication between the patient and her caregivers. Lower rates of PTB have been reported in observational studies of provider-initiated contact,110 family nurse partnerships, and special programs for women with previous PTB.111 Because the clinical presentation of preterm parturition is more subtle than parturition at term, early signs and symptoms such as pelvic pressure and

The future of prenatal care for women with prior PTB

Selective use of progestational agents and cerclage112 is guided primarily by a clinical history of spontaneous PTB or repetitive midpregnancy loss, respectively. Neither is fully effective in all women with these historical indications. As experience with progesterone supplementation grows, prophylaxis may be reserved for women with a prior PTB who also manifest another marker for PTB, such as a short cervix, a positive test for cervical inflammation, and/or who are found to have a genetic

Key points that summarize the authors' approach to prenatal care for women with a prior preterm birth

  • Obtain a thorough history and records for all prior pregnancies.

  • Try to determine the pathways that led to the prior PTB and categorize it as likely or unlikely to recur.

  • Estimate the woman's personal risk of another PTB.

  • Identify and eliminate or minimize other risk factors.

  • Establish welcoming methods of communication between women with prior PTB and knowledgeable caregivers.

  • Assess personal and family resources and barriers to receiving care.

  • Apply evidence-based interventions for women with prior

Acknowledgments

Dr Berghella is currently participating in a prospective trial of vaginal progesterone to prevent preterm birth in high-risk women sponsored by Columbia Laboratories, makers of the product being studied in the trial. Neither of the authors receives money from, owns stock in, or speaks on behalf of Columbia Laboratories.

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