Objective: Investigation of daytime sleepiness, blood pressure changes and presence of sleep disordered breathing, in healthy young women during pregnancy.Methods: Young, healthy pregnant women between 18 and 32 years of age, seen in three different prenatal care clinics, were enlisted in a prospective study divided in two parts: part 1 of the study consisted of completing a standardized questionnaire on past and present sleep disorders. It also included filling out visual analog scales (VAS) for daytime sleepiness and snoring by the subject and bed partner. Blood pressure measurement was performed at 9 AM as per the WHO protocol. Similar data were collected again at the 6-month prenatal visit and at the 3-month post-delivery visit. At the 6-month visit, ambulatory monitoring of nocturnal sleep using a portable six-channel recorder (Edentrace((R))) was performed at home. Part 2 involved a subgroup of subjects that were randomly selected after stratification based on results of VAS and ambulatory monitoring. It included 1 night of nocturnal polysomnography with esophageal manometry and 24 h of ambulatory BP monitoring with portable equipment with cuff inflation every 30 min.Results: Of the 267 women who participated in part 1 of the study, only 128 consented to enroll in part 2, from which 26 were selected to undergo polysomnography. At the 6-week prenatal visit 37.45% of the subjects reported daytime sleepiness of variable severity. At the 6-month visit, this was noted in 52% of the subjects. Bed-partners reported chronic, loud snoring prior to pregnancy in 3.7% of the study population, but this increased to 11.8% at the 6-month visit. Blood pressure (BP) remained below the pathological range, i.e. less than 150/95 mm Hg, during the entire pregnancy. However, ambulatory monitoring indicated that 37 women, including the loud chronic snorers, had some minor SaO(2) drops during sleep and this same group presented the largest increase in BP between the 6th week and the 6th month prenatal visits. Part 2 included 26 women, 13 from the above identified 37 women and 13 from the rest of the group, chosen randomly, age and body mass index (BMI) matched. Polysomnography did identify two abnormal breathing patterns during sleep: (1) esophageal pressure 'crescendos' associated predominantly with stage 1 and 2 NREM sleep, and (2) 'abnormal sustained efforts' seen predominantly with delta sleep. These abnormal breathing patterns were noted during a significantly longer time during sleep. This group of women with the abnormal breathing patterns were not only chronic snorers but also had significantly higher systolic and diastolic BP increases when compared to the 13 other non-snorers. Six out of the 13 snorers were 'non-dippers' at the 24-h BP recording.Conclusion: Abnormal breathing during sleep (that is frequently, but not always, associated with loud, chronic snoring, and may be a consequence of edema induced by hormonal changes associated with pregnancy), can be seen in otherwise healthy young pregnant women. It may contribute to the symptom of daytime sleepiness. The changes in blood pressure noted were of no pathological significance in our population but could be an added risk factor in high-risk pregnancies.