Does bed rest prevent preterm birth?

One in 3 women nulliparous women with a short cervix is prescribed some type of activity restriction, despite lack of benefit in prevention of preterm birth (PTB). Those are the findings from a secondary analysis of data from the Short Cervix and Nulliparity trial. Published in Obstetrics & Gynecology, it is accompanied by a commentary titled “Bed Rest in Pregnancy: Time to Put the Issue to Rest” and an ethical argument for dismissing the practice.

In the Short Cervix and Nulliparity trial, asymptomatic nulliparas with singleton gestations and cervices <30 mm were randomized to either weekly intramuscular 17-α hydroxyprogesterone caproate or placebo. The secondary analysis looked at the women’s responses to weekly questions about whether they had been placed on pelvic, work, or nonwork rest.

Of the 657 women in the trial, 646 (98%) responded to the activity restriction questions and 252 (39% were placed on any activity restriction at median of 23.9 weeks (interquartile range 22.6-27.9 weeks). Activity restriction was more likely to be prescribed if a woman was older (P<.001), had private insurance (P=.01), was not Hispanic (P<.001), or had funneling and intra-amniotic debris. PTB at <37 weeks was more common in those who were placed on activity restriction (37% vs 17%, P<.001). PTB remained more common in the activity restriction group even after the investigators controlled for potential confounding factors (adjusted odds ratio 2.37; 95% CI, 1.60-3.53). Similar results were seen for PTB at <34 weeks’ gestation.

The authors note that activity restriction “was not always more likely to be prescribed to women with characteristics most associated with preterm birth” and that it is “dependent not only on the perception of risk status, but on social factors as well.” Their analysis, they conclude, “emphasizes the importance of conducting an adequately powered randomized trial for women at increased risk of preterm birth such that level I evidence for the effects of activity restriction can be obtained.”