Sleep-disordered breathing and snoring are common in pregnancy. The aim of this study was to determine whether pregnancy was associated with upper airway narrowing. One-hundred females in the third trimester of pregnancy were recruited and 50 agreed to be restudied 3 months after delivery. One-hundred nonpregnant females were also recruited. Upper airway dimensions were measured using acoustic reflection. Snoring was less common in nonpregnant (17%) than pregnant females (41%; odds ratio (OR) 3.34; 95% confidence interval (CI) 1.65-6.74) and returned to nonpregnant levels after delivery (18%; OR 0.15; 95% CI 0.06-0.40). Pregnant females had significantly smaller upper airways than nonpregnant females at the oropharyngeal junction when seated (mean difference 0.12; 95% CI 0.008-0.25), and smaller mean pharyngeal areas in the seated (mean difference 0.14; 95% CI 0.001-0.28), supine (mean difference 0.11; 95% CI 0.01-0.22) and lateral postures (mean difference 0.13; 95% CI 0.02-0.24) compared with the nonpregnant females. Pregnant females had smaller mean pharyngeal areas compared with post-partum in the seated (mean difference 0.18; 95% CI 0.02-0.32), supine (mean difference 0.20; 95% CI 0.06-0.35) and lateral postures (mean difference 0.26; 95% CI 0.12-0.39). In conclusion, this study confirmed increased snoring and showed narrower upper airways during the third trimester of pregnancy.