Background: Pregnancy is associated with dilatation of the collecting systems of the kidneys. However in most pregnant women hydronephrosis goes un-recorded and may only become evident when symptoms develop. The incidence of hydronephrosis in pregnancy is yet to be determined in our environment hence the need to determine the incidence and associated factors in Port Harcourt. This study was done to evaluate pregnant women in the second and third trimesters and to determine the incidence of hydronephrosis with respect to parity, gestational age and commonest side of occurrence. Materials and Methods: A prospective, descriptive cross sectional study involving 190 pregnant patients referred to the Radiology Department of the University of Port Harcourt Teaching Hospital between August 2012 and July 2013. Their demographic data and Ultrasonographic findings were obtained. Data was analyzed using statistical package for social sciences (SPSS) version 20. Results and Discussions: The ages of the women ranged from 18 to 42 years however the age group (27 – 30) years had the highest incidence of hydronephrosis of pregnancy. Of the 190 pregnant women, 74 were in their second trimester of pregnancy and 116 were their third trimester. Thirty three percent of the patients in the study group has normal Right pelvicalyceal diameter while 66.3% has Right pelvicalyceal dilatation. 51.1% has normal Left pelvicalyceal diameter and 48.9% has Left pelvicalyceal dilatation. Pearson correlation test shows a positive but not significant correlation between gestational age and both Right pelvicalyceal dilatation (p= 0.416) and Left pelvicalyceal dilatation (p= 0.191). Conclusions: Hydronephrosis of pregnancy is common and predominantly occurs on the right. Pelvicalyceal dimensions increases throughout pregnancy with increasing gestational age as well as increasing parity.