This may shock you, but there is no evidence that bed rest does anything to prevent preterm birth or help with any other health condition of pregnancy, including placenta previa, pre-eclampsia, preterm premature rupture of membranes (pPROM), or shortened cervix.
Really, truly. No evidence that bed rest helps. And this has been known for a long time.
Preventing Preterm Birth
(image from Babble)
The American Congress of Obstetricians and Gynecologists (ACOG) published the following recommendation in 2003, which was reaffirmed in 2012:
Bed rest and hydration have not been shown to be effective for the prevention of preterm birth and should not be routinely recommended.*
Got that? Not effective. Should not be routinely recommended.
The Cochrane Collaboration, which sets international standards for evidence based medicine by reviewing randomized control trials (considered the “gold standard” in medical research), says of bed rest for preterm labor,
Due to the potential adverse effects that bed rest could have on women and their families, and the increased costs for the healthcare system, systematic advice of bed rest for preventing preterm birth should not be given to pregnant women.
The World Health Organization reports on the largest known randomized control trial of bed rest for preventing preterm labor:
For the purpose of comparing the effects of bed rest to no bed rest, 432 women allocated to bed rest at home were compared with a control group …422 had received no intervention. Incidence of preterm birth prior to 37 weeks was similar in both groups.
Here are the conclusions on the efficacy of bed rest from a series of articles posted on Medline:
Bed rest is used extensively to treat a wide variety of pregnancy conditions, at substantial cost but with little proof of effectiveness (Goldenberg, et al).
We should not assume any efficacy for bed rest. (Glaziou and Del Mar)
Mitigating Medical Conditions in Pregnancy
There is no evidence base for bed rest for conditions other than preterm birth risk either. Here is what ACOG guidelines say about bed rest for hypertension/pre-eclampsia (high blood pressure in pregnancy):
There is little evidence of the efficacy of nonpharmacologic management of hypertension in pregnancy. Whether bed rest is efficacious requires more research, including larger trials, and the risks of immobilization for long periods of time (e.g. thromboembolic events [blood clots, etc]) must also be addressed.
Update: I have a full post on preeclampsia here.
On placenta previa, for which hospital bed rest is often prescribed, Cochrane says,
[T]here are only trials of cervical cerclage (‘tying’ the cervix), and the effects of hospitalisation. The review found that cervical cerclage may reduce very premature births, although the evidence was not strong. There is little evidence of advantages or disadvantages to hospitalisation.
Regarding threatened miscarriage, and multiple gestations (e.g. twins or triplets), and preeclampsia, in addition to preterm labor, Drs. Bigelow and Stone of Mount Sinai School of Medicine in New York write,
Although the use of bed rest is pervasive, there is a paucity of data to support its use. Additionally, many well-documented adverse physical, psychological, familial, societal, and financial effects have been discussed in the literature. There have been no complications of pregnancy for which the literature consistently demonstrates a benefit to antepartum bed rest.
The evidence is unwavering. There is no known benefit of bed rest in pregnancy. Even if bed rest has no associated harms, if it has no benefit, why bother? When we have two options with equal outcomes, one involving living life normally, and one involving a major life alteration that is inconvenient, expensive, and boring, why would anyone choose the latter?
*All emphasis in quotes throughout the post is mine
Update: WebMD has a new piece on bed rest for preventing preterm birth that actually provides evidence based information here.