Introduction:Pregnancies can be either planned or unplanned. Unplanned pregnancies are a major public health issue globally causing poor maternal and foetal outcomes. Addressing this problem would improve the well-being of antenatal mothers and their children. Family planning is an important step to minimise the burden of unplanned pregnancies.Objective: To determine the prevalence of unplanned pregnancies and their family planning preferences in the Thimbirigasyaya Divisional Secretariat Division. Methods:A cross-sectional study was conducted in three randomly selected antenatal clinics (Borella, Kirula and Wellawatte) which covered District 3, District 4 and District 5 Medical Officer of Health (MOH) areas of Thimbirigasyaya Divisional Secretariat Division of the Colombo Municipal Council. A total of 425 antenatal mothers who attended these antenatal clinics, fulfilling the inclusion and exclusion criteria were included in the study using a consecutive sampling method. Data collection was done by the principal investigator using interviewer-administered questionnaires. Data on prevalence and family planning preferences following current pregnancy were obtained and analysed. The prevalence of unplanned pregnancies was calculated based on responses given to questions on the timing and decision-making of the current pregnancy. Family planning practices and preferences were calculated as percentages. Results:The total sample size of 425 included a ten percent nonresponse rate. The age distribution was between 15 to 44 years. The age group of 22 to 34 years included 83.2% of the total study population. There were 37.2% Sinhalese, 33.9% Moors and 28.9% Tamils in the study sample. The prevalence of unplanned pregnancies was 32.7%.Thirty-three percent of antenatal mothers had used some form of contraceptive method in the past and most of them had used condoms and depot-medroxyprogesterone acetate (DMPA), closely followed by combine oral contraceptive pills, implants and intrauterine devices. Side effects were the major reason for not using a method in the past among nonusers. Around 60% have decided to use a contraceptive method following the current pregnancy and the majority have decided to use their chosen method for two to five years. Conclusions:According to the study, one-third of the pregnancies at antenatal clinics in the Thimbirigasyaya Divisional Secretariat Division were unplanned pregnancies. One-third of the mothers had used a contraceptive method in the past and the main reason was to space their pregnancies. More than half of the participants were planning to use a contraceptive method following the current pregnancy and many had chosen depot-medroxyprogesterone acetate (DMPA). Among future users, half had preferred to use their chosen method for two to five years, while among nonusers, side effects were considered the main reason for not planning to use a contraceptive method in the future.Recommendations: According to the study, one-third of the pregnancies at antenatal clinics in the Thimbirigasyaya D...