In this study 500 obese pregnant women and 250 non-obese pregnant women (Group of Control) were followed up to prove the role of obesity as a high risk factor on the incidence of (P.I.H.). We found that: 1. There is a considerable increase in the incidence of (P.I.H.), which was proportional to the grade of obesity in the main group. The incidence of P.I.H. was : %15.38 in grade 1, %26.42 in grade 2 and %42.22 in grade 3 of obesity (Vs. %6.4 in the control group). 2. There is a considerable increase in the incidence of (P.I.H.) among the obese pregnant women, especially when they are 36-45 years old (%32.39 Vs. %6.45 in control group). So that it is advisable to screen all obese pregnant women especially when they are 36-45 years old and consider them as a high risk group for the indicence of (P.I.H.).