Background/Aims Maternal, fetal and child health are of key public health concerns, globally. Both pregestational body mass index and gestational weight gain are critical players in maternal health, fetal development and delivery outcome. This study investigated the association between maternal assumed pregestational body mass index, gestational weight gain and outcomes of deliveries among puerperal mothers in the Tamale metropolis of Ghana. Methods A cross-sectional randomised descriptive study was conducted at the postnatal and neonatal intensive care units of the state-owned hospitals in the Tamale metropolis. The mothers' body mass index at their first antenatal care clinic was assumed to be their pregestational body mass index. Maternal gestational weight gain was calculated using the last gestational weight before onset of labour. Participants also responded to structured questionnaires with questions on their sociodemographic characteristics and intra-pregnancy behaviours. Additionally, information on their obstetric and gynaecological history, and their delivery outcome were collected. Data were analysed using descriptive statistics and chi-squared tests, with significance set at P<0.05. Results A total of 450 puerperal mothers were involved in this study with a mean age of 29±1.79 years. Maternal body mass indexes at first antenatal clinic visit were predominantly typical (41.8%) or overweight (42.0%). At delivery, 46.4% of mothers had typical gestational weight gain, while the majority (53.6%, P=0.0387) had anomalous gestational weight gain. Strikingly, 72.9% of mothers who had a healthy body mass index at the first antenatal clinic visit experienced anomalous gestational weight gain. Caesarean section delivery was significantly prevalent among pregnant women who had typical gestational weight gain (P=0.0014). Also, episiotomy was significantly linked to typical gestational weight gain (P=0.0448), but not mothers who were overweight before conception (P=0.2692), irrespective of their gestational weight status. Conclusions Anomalous gestational weight gain is high among puerperal mothers in the Tamale metropolis, and suggests contributory roles in adverse maternal and fetal health. A comprehensive gestational weight management education programme for women in the metropolis could help curb the burden of anomalous gestational weight gain.