During pregnancy, the various changes women undergo can affect their health status. Manual therapies are important aids because they do not use medication. This study aimed to evaluate the influence of osteopathic manipulative treatment on the intensity of lumbar and pelvic pain and changes in quality of life. This prospective study included women over 18 years old and between 27 and 41 weeks pregnant, and excluded women with fetal malformations, multiple fetuses, premature rupture of membranes, and in labor. Forty-six pregnant women were selected and divided into two groups of ≤3 and ≥4 visits. Statistically significant improvements were observed in the intensity of maximum low back pain (7.54 ± 1.47 vs. 3.815 ± 1.73, p ≤ 0.01) and minimum low back pain (5.67 ± 2.03 vs. 3.111 ± 1.67, p ≤ 0.01), maximum pelvic pain (6.54 ± 2.22 vs. 2.77 ± 1.64, p = 0.01), and minimum pelvic pain (5.615 ± 2.21 vs. 2.615 ± 1.66, p = 0.01). Both groups achieved improvements in quality of life indices, with the improvements achieved by the ≥4-visits group being statistically significant. Osteopathic treatment was effective in reducing the intensity of lumbar and pelvic pain and in improving the quality of life of pregnant women in the third trimester.