Aim: The study was to determine the effect of maternal periodontal status on birth weight. Materials and Methods: This longitudinal study was conducted at the University of Benin Teaching Hospital, Benin City, Edo State. Recruited into the study were 300 pregnant women aged between 20 and 34 years who were randomly placed into two groups. Test group received oral prophylaxis upon enrolment and control group received prophylaxis after deliveries. The gestational age for enrolment was from 12 weeks to 36 weeks. The groups were balanced for other risk factors, while smoking and alcohol was assessed using the questionnaire. The participants were all primigravid women. Data were collected by means of interviewer-administered questionnaire, clinical dental examination and participants′ hospital records. Results: Community Periodontal Index (CPI) assessment revealed that 44.4% recorded code 2; 22% had code 3; while 16.6% had code 4. The overall prevalence of low birth and normal weight in this study were 6.3% and 93.8% respectively. The prevalence of low birth weight (LBW) among the test and control group were 0.0% and 12.5% respectively. The highest prevalence of low birth weight delivery (27.3%) among the control group was among the participants with CPI score 4 which was statistically significant ( P <0.05). Conclusion: The study revealed that the control group had low birth weight deliveries, which was significantly associated with poor periodontal status. Therefore, there is the need for oral prophylaxis among pregnant women preferably before second trimester.