"The Washington Post" reported in 2001 that researchers have not found sows in gestation crates to have elevated levels of stress hormones. The paper notes that this suggests their overall health is not compromised. Some producers in Europe use a “free access” maternity pen configuration in which sows are in individual pens for the first four weeks of pregnancy but can “unlock” the stall by backing out and entering a common area. The producers observed that pregnant pigs will stay in the individual pens more than 90 percent of the time, and return to the same stall more than 90 percent of the time.