Background: The normal structure and function of the pelvic floor may be disrupted by pregnancy's hormonal and mechanical changes. One trustworthy method for demonstrating these alterations in near-term primigravid females is the use of 3D trans-perineal ultrasonography. So, we aimed to assess pelvic floor biometrical measurements of primigravid women using 3D trans-perineal ultrasound and the effects of pregnancy on them. Methods: This observational cross sectional study was carried out on 104 patients without symptoms of Pelvic floor disorders (PFDs), chronic cough, and long-term constipation, attending Fetal medicine and Ultrasonography Unit, Department of Obstetrics & Gynecology at Zagazig University Hospitals and were divided into two groups; the primigravidae (Study group) and the nulliparous (Control group). Three-dimensional trans-perineal ultrasound was done for all subjects. Results: There was an increase in bladder neck descent in primigravid women, and a higher bladder neck position at both rest and Valsalva in nulligravid women. There was also a statistically significant difference in alpha angle, retro-vesical (beta) angle, levator hiatus area between the two groups with higher values in the primigravid group. Furthermore, there was higher number of participants showing funneling of the proximal urethra in the primigravid group. Conclusion: Our study suggests that pregnancy itself can have its impact on the pelvic floor biometry as there are significant differences between near term primigravid women (equal to or above 32 weeks gestation) and nulligravid women.