My wife weight is 70 her height is 5.4 ft. is this necessary to loose weight for pregnancy.?

The BMI chart: We only use height and wt to determine healthy vs not-healthy-wt ranges for both men and women. It is a rough estimate and provide you a guide to keep "ideal body wt" for better health. In her case, she is a bit overweight and so she should try not to gain too much during pregnancy--otherwise wt loss is not really needed for pregnancy in her case. Consult doc. Good luck.