Peak expiratory flow rate in normal pregnancy.

Objective: To determine whether peak expiratory flow rate changes with pregnancy and advancing gestation.

Methods: We measured the peak expiratory flow rate in 57 women during each trimester of pregnancy and postpartum. During four visits, all subjects exhaled forcefully three times into a peak flow meter. For each visit, the best of three attempts defined their peak expiratory flow rate. Using accepted standard nomograms, we normalized peak expiratory flow rate with respect to height and age. Using analysis of variance, we compared the mean normalized peak expiratory flow rates in each of the trimesters and postpartum.

Results: The subjects' peak expiratory flow rates did not change significantly during the three trimesters and postpartum (P = .317). The mean peak expiratory flow rates for the three trimesters and postpartum were 434 +/- 18, 452 +/- 16, 444 +/- 15, and 450 +/- 16 (values in liters per minute +/- 95% confidence intervals [CIs]). The mean normalized peak expiratory flow rates for the three trimesters and postpartum were 0.92 +/- 0.036, 0.95 +/- 0.032, 0.94 +/- 0.030, and 0.95 +/- 0.031 (values +/- 95% CI).

Conclusions: This study demonstrates that peak expiratory flow rate does not change with pregnancy and advancing gestation. Therefore, testing peak expiratory flow rate in pregnancy is valid, and physicians can use peak expiratory flow rate accurately and reliably in the management of pregnant women with asthma.