The quality of sleep during pregnancy gradually worsens, with research indicating that it is poorest in the third trimester. Sleep problems in the third trimester arise due to physical and hormonal changes. The main causes of sleep disturbances linked to physical changes include back pain, frequent urination, difficulty finding a comfortable sleeping position, and increased body weight. Hormonal variations, such as elevated progesterone levels, can lead to reduced deep sleep and increased frequency of awakenings during the night. The relaxation of muscles, associated with higher levels of progesterone and relaxin, may also increase the risk of obstructive sleep apnea, further disrupting sleep quality. Studies confirm more frequent awakenings and longer sleep onset latency as pregnancy progresses. Additionally, fear of childbirth and concerns regarding the outcome of the pregnancy further exacerbate sleep problems, particularly in the third trimester when labor is imminent. The impact of pregnancy planning on sleep quality has not been previously investigated. The aim of this study was to examine whether there are differences in sleep quality across different trimesters of pregnancy, as well as differences in sleep quality concerning the planned versus unplanned nature of the pregnancy. The study included 743 participants, of whom 61 were in the first trimester, 235 were in the second trimester and 447 were in the third trimester. The age range of the pregnant participants was from 18 to 47 years. The research was conducted using Google Forms, where participants completed a general information questionnaire and the Pittsburgh Sleep Quality Index. The results indicated that the poorest sleep quality was reported by pregnant women in the third trimester compared to those in the first and second trimesters. Additionally, there was no difference in sleep quality with regard to pregnancy planning.