Activity restriction is 1 of the most common interventions used in obstetrics. Although it is used for many reasons, 1 of the most common is to prevent preterm birth in those at risk. This review of the literature describes the potential advantages, disadvantages, and efficacy of activity restriction for the prevention of preterm birth.
The prescription of maternal activity restriction is one of the most widely used interventions in obstetrics, with as many as 95% of obstetricians reporting having used it in their practice. Approximately 18% of pregnant women are placed on activity restriction sometime during their pregnancy. Whereas maternal activity restriction is prescribed to pregnant women for a variety of reasons, such as vaginal bleeding, fetal growth restriction, and hypertension during pregnancy, the focus of this review will be on the evidence to support its use to prevent preterm birth in those at risk.
In the Cochrane database, the authors observed that bed rest is the customary initial therapy for women at risk for preterm birth. The American College of Obstetricians and Gynecologists recommend that a physically active woman at risk for preterm labor should be advised to reduce her activity.
In a recent survey of members of the American College of Obstetricians and Gynecologists 34%, 37%, and 39% of obstetricians prescribed bed rest for a shortened cervical length (<2.5 cm), cervical funneling, and vaginal fetal fibronectin positivity, respectively. A 2007 survey of Canadian obstetricians, family practitioners, and midwives found that 72.3%, 77.2%, and 67.1% used activity restriction in their practices, despite approximately two-thirds of respondents answering that the evidence that activity restriction prevents preterm birth was in the fair to poor range. Lastly, in a 2007 survey of members of the Society of Maternal-Fetal Medicine, more than 80% of the members prescribed bed rest for women at risk for preterm birth.
It is clear that maternal activity restriction is 1 of if not the most common interventions used to prevent preterm birth in women at risk. The frequency of its use is likely based on the perception that there is little harm in placing a woman on activity restriction and that uterine contractions, cervical effacement, and dilatation are related to maternal activity levels. Furthermore, there is likely a “do as my colleagues do” approach when using activity restriction.
One of the often overlooked negative effects of activity restriction is the economic effects, with the majority of pregnant women in the United States employed; the financial burden alone from placing pregnant women on activity restriction was estimated at 5.7 billion dollars a year (1994). This has likely increased significantly using both current dollars and recognizing the increased number of women in the workplace.
Defining activity restriction
Bed rest is the most commonly used term when a woman is placed on activity restriction, yet there is no standard definition of bed rest. There are varying definitions listed in studies that have examined the effectiveness of bed rest including rest 3 times a day for an hour, no more than 1-2 hours a day out of bed, and bed confinement with the exception of bathroom use.
Inconsistency in the definition of activity restriction in the literature undermines the ability to study the efficacy of activity restriction to decrease preterm birth. Furthermore, although the most common terms used in the literature are bed rest or activity restriction, other terms including lifestyle modification, rest, and hospital confinement are commonly used without definition. The lack of consistency in the terms and definitions of activity restriction is prevalent in the counseling and advising of pregnant women.
To conduct meaningful research in this area and to provide consistent patient care and health care provider communication, it is important to be consistent in our terms and definitions. It seems most prudent to abandon other terms and solely use the term activity restriction. To create a meaningful intervention that can be used both clinically and for investigation, it must be generalizable and have a standard definition. The Table divides activity restriction into 3 increasing levels, which will allow standardization.
| Type of activity restriction | Definition |
|---|---|
| Light | One hour or less of continuous rest, in bed or in the sitting position during waking hours, and no lifting of >10 lb. |
| Moderate | More than 1 hour but <8 hours of continuous rest during waking hours with no household chores and no lifting. Health-related visits are allowed. |
| Strict | Confinement to their dwelling except for health care-related visits. Rest in the sitting or supine position the entire day. No household chores or lifting. |
Efficacy of activity restriction in preventing preterm birth
The use of activity restriction as a therapeutic modality dates back to Hippocrates: “Rest as soon as there is pain, it is a great restorative in all disturbances of the body.” In the late 1800s, Hinton published the first book on activity restriction as a therapeutic option. However, in the modern era, sick people rarely went to bed for fear of loss of income. The effectiveness of dictated activity restriction as a therapy has been debated since the 1800s, and the beginning of its application to the obstetrical population is unclear.
There have been few studies examining the potential benefit of activity restriction for the prevention of preterm labor. In 1983, Berkowitz et al performed a postpartum survey on 175 women who had a preterm delivery and compared it with 313 women who delivered at term. There was no difference in standing or moving periods, child care, occupational activities, or number of household chores between the groups. However, women who participated in sports or physical activity had a decreased rate of preterm birth. This led the authors to the conclusion that employment, housework, child care, and leisure time exercise during pregnancy did not increase the risk of preterm birth.
In contrast, at least moderate forms of exercise may be beneficial, perhaps decreasing the risk of preterm birth. These findings are consistent with a recent population-based study, which found a decrease risk of preterm birth in women who participated in strenuous physical activity and competitive sports or vigorous leisure activity.
The Europop study was a large population-based study of deliveries occurring in several European centers. They compared work conditions in more than 5000 women who had a preterm birth vs almost 8000 women who had a term birth and found that women who had a preterm birth were more likely to perform manual labor, have more than a 42 hour work week, report prolonged standing, and have poor job satisfaction. However, these findings are not universal, with some population-based studies finding no difference in work-related conditions and preterm birth.
In a recent metaanalysis examining work conditions and adverse pregnancy outcomes, Mozurkewich et al reported an increased risk of preterm birth in women who engaged in prolonged standing, shift work, and physically demanding work and had an increased fatigue score.
In a randomized trial, Hobel et al sought to evaluate a preterm prevention program including education, increased clinic visits, and selected prophylactic interventions to reduce preterm birth. The authors randomized 8 west Los Angeles prenatal clinics. Five clinics were placed in the experimental clinics grouping and 3 were used as controls. Women in the 5 experimental clinics received increased frequency in prenatal visits, preterm birth prevention education, psychosocial and nutritional screening, and crisis intervention. The experimental clinics were randomized again to 1 of the following interventions: bed rest, defined as resting for 3 times a day for an hour; psychosocial support and an oral progestin group in which they were randomized again to either 20 mg of medroxyprogesterone acetate (MPA, Provera; Pfizer, New York, NY) or to placebo.
One thousand seven hundred seventy-four patients were entered into the trial. The rate of preterm birth in the experimental clinics was 7.4% vs 9.1% in the control clinics (odds ratio, 0.78; 95% confidence interval, 0.58–1.04; P = .045). Of note, women in the MPA-exposed group had a higher rate of preterm birth (17.6% vs 6.1%), although this was attributed to a lack of compliance. Power was limited in this trial, with a 77% chance of detecting a 30% difference in preterm birth with an alpha error of 0.05, leading the authors to conclude that there was insufficient sample size for definitive conclusions to be made based on trial results.
In a more recent trial, women with symptoms of preterm labor, a negative vaginal fetal fibronectin and less than 3 cm dilatation were tocolyzed and randomized to either activity restriction or no restriction. Activity restriction was defined as bed confinement except for use of the bathroom and physician visits. Thirty-eight women were randomized to the activity restriction group and 41 to the nonactivity restriction group. There was no difference in the rate of preterm delivery between the groups.
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