Fractioned exhaled nitric oxide (FE(NO)) is not a sufficiently reliable test for monitoring asthma in pregnancy.

It has been reported that fractioned exhaled nitric oxide (FENO) can be used for monitoring airway inflammation and for asthma management but conclusions drawn by different researchers are controversial. The aim of our study was to evaluate the clinical usefulness of FENO assessment for monitoring asthma during pregnancy. We monitored 72 pregnant asthmatics aged 18-38years (Me=29 years) who underwent monthly investigations including: the level of asthma control according to GINA (Global Initiative for Asthma), the occurrence of exacerbations, ACT (Asthma Control Test), as well as FENO and spirometry measurements. In 50 women, during all visits, asthma was well-controlled. In the remaining 22 women, asthma was periodically uncontrolled. FENO measured at the beginning of the study did not show significant correlation with retrospectively evaluated asthma severity (r=0.07; p=0.97). An analysis of data collected during all 254 visits showed that FENO correlated significantly but weakly with ACT scores (r=0.25; p=0.0004) and FEV1 (r=0.21; p=0.0014). FENO at consecutive visits in women with well-controlled asthma (N=50) showed large variability expressed by median coefficient of variation (CV)=32.0% (Min 2.4%, Max 121.9%). This concerned both: atopic and nonatopic groups (35.5%; and 26.7%, respectively). Large FENO variability (35.5%) was also found in a subgroup of women (N=11) with ACT=25 constantly throughout the study. FENO measured at visits when women temporarily lost control of asthma (N=22; 38 visits), showed an increasing tendency (64.2 ppb; 9.5 ppb-188.3 ppb), but did not differ significantly (p=0.13) from measurements taken at visits during which asthma was well-controlled (27.6 ppb; 6.2 ppb-103.4 ppb). The comparison of FENO in consecutive months of pregnancy in women who had well-controlled asthma did not show significant differences in FENO values during the time of observation. The assessment of asthma during pregnancy by means of monitoring FENO is of limited practical value due to this parameter's considerable intrasubject variability, regardless of the degree of asthma control.