Background: Extremes of weight could have an effect on the mother and her newborn. Obesity is no longer a problem of only Caucasian women, as it is also now a public health concern in women of African descent. Maternal underweight appears to also affect pregnancy and perinatal outcomes. The aim of this study was therefore to examine the effect of overweight and obesity on maternal and perinatal outcomes. Methods: This is a retrospective descriptive study among women who delivered at the Department of Obstetrics and Gynaecology, University of Benin Teaching Hospital (UBTH), Benin City, Nigeria, from January 1, 2022 to December 31, 2022. Results: The mean age of the women was 30.7 years (standard deviation 5.1). Most of the low-birth-weight babies were born to overweight women, and the relationship was statistically significant (p = < 0.001). Among the eight neonates who died, seven were born to normal-weight and overweight mothers. Many of the neonates admitted into SCBU were born to overweight mothers, and the test of association was statistically significant (p = < 0.001). A significantly large proportion of those who had complications during the antenatal and postpartum period were obese women (p = 0.053). Conclusion: The odds of low birth weight were significantly higher among overweight mothers compared to mothers who had healthy weight. Obese women were significantly more likely to have antenatal and postpartum complications relative to normal healthy weight women.