This randomized controlled clinical trial will assess the impact of intermittent fasting on the incidence of gestational DM in obese pregnant women in 3rd trimester and its effect on maternal and neonatal outcomes.

The term intermittent fasting, when used for health reasons or weight loss, has been used to describe various types of caloric restriction. Some authors use it when a patient withholds caloric intake for several consecutive hours during the day (often 16 h with all energy intake during the other 8 h of the day, others for a full day once or twice a week , and others three or four days per week Some protocols allow protein intake but no carbohydrates and still label it intermittent fasting.

Others allow carbohydrates or macro/micro-nutrients up to a limit that will still promote ketosis and, although it is simply a low-calorie diet, due to the popularity of fasting this has been labeled a diet that mimics fasting.

In this protocol we use 16hour fasting in 24hour with the same caloric intake in 8hour and can drink water ,coffee , and other noncaloric beverages during the fast, which can help reduce feelings of hunger .

In all instances, non-caloric fluid intake is permitted (which is one of the main differences when compared to religious fasting) and therefore significantly reduces the risk of dehydration and hypotension, a prominent consideration in religious fasting.

During the fasting hours and after breaking the fast, metabolic condition of the body could be influenced as a consequence of change in the pattern and amount of activity, meals and fluid intake, and even sleeping hours.

Intermittent fasting and low caloric intake have been shown to improve various metabolic and inflammatory pathways. Insulin resistance, the most prominent feature of type 2 diabetes during pregnancy, has long been known to improve with intermittent fasting. After a period of fasting, insulin sensitivity rises and insulin levels fall. These result in improved fasting and postprandial glucose levels. In addition, as insulin induces adipose tissue growth, there is less propensity to weight gain and potentially even weight loss which leading to decrease neonatal adverse effects of gestational DM and improved fetal outcome.

On the other hand, many other studies found that fasting has no effect on intrauterine growth, birth weight, birth-time indices, gestational diabetes, preterm birth, and preeclampsia. Predominantly, results of the studies examining the effects of fasting on mothers and newborns are not homogenous; therefore, further research should be conducted to attain valid findings.

Inclusion Criteria:

- 1. Healthy pregnant women. 2. Age (18 - 35 years old). 3. Women with BMI (_> 30 kg/m2).

4. A living singleton pregnancy. Gestational age (24- 27 weeks).(recruitment time)

Exclusion Criteria:

- 1. Multiple gestations. 2. Women with diabetes 3. pre-pregnancy cardiovascular disease, chronic hypertensive, and pregnancy-induced hypertension; blood pressure _> 140/90.

4. Women with hepatic, renal diseases or coagulopathy 5. Women with peptic ulcer.