India's top IT firms have seen many of their employees leaving the companies in the past few quarters, even as they increase their size and expand operations every year.

Tata Consultancy Services (TCS), Infosys and Wipro have together witnessed a total of more than 100,000 employees quitting their jobs in the past four quarters.

While the combined gross addition of employees by the three companies was about 150,000, net addition stood between 40,000 to 50,000, The Economic Times reported.

However, parameters like gross addition of employees are fast becoming "irrelevant" as the company tries to contain attrition levels in the current context of automation and other emerging new technologies in the Indian IT industry, according to a few CEOs of domestic top 10 outsourcing companies.

Higher attrition levels of 19%-20% are becoming a "new normal" for the major IT companies as compared to low attrition rates and high growth rates seen until a few years ago.

"In FY10, we had a revenue of $6.3 billion with a headcount of 160,000. In FY15, we doubled the headcount to 320,000. But the revenue did not just double. We generated revenues of $15.5 billion, representing a productivity gain of nearly $3 billion," CEO of TCS N Chandrasekaran had said in a keynote speech at the Morgan Stanley Annual India Summit last month.

Industry body Nasscom estimates that the domestic IT industry hired 14,350 engineers for "each billion dollars in revenues" in FY15 as compared to a hiring of 38,000 engineers in 2003.

India's second largest IT firm Infosys' attrition rate stood at 18.9% in the last fiscal year, ending March 2015, rising sharply from 13.4% recorded in fiscal year 2009-10.

In the June quarter alone, Infosys saw 8,553 employees leaving the company, while it added 3,336 employees.

The country's largest software firm TCS lost around 15,000 people in the April-June quarter, nearly twice the number of employees who quit Infosys. TCS made a net addition of about 5,279 employees during the quarter.

Similar is the case for India's third largest IT firm Wipro, which saw nearly 12,500 people resigning their jobs in the quarter. Wipro recorded a net addition of just over 3,000 employees.

The current trend is in contrast to the picture that prevailed for many years during the 2000s. During those years, the companies used to hire more than "tens of thousands of engineers" annually, at the same time witnessed low attrition levels.

The change is mainly driven by automation tools and new technologies like cloud computing, which result in enhanced productivity levels.

"We rolled out the Infosys Automation Platform within infrastructure management service to the first 10 clients and we saw productivity improvement of up to 37% and people savings of up to 17% in those cases," Infosys CEO Vishal Sikka had said last week.