Clegg's comments come as a study published today, by website Mumsnet revealed 60% of women felt less employable since having a child and 75% said it was harder to progress in their career.
The study of more than 1,000 users of the parenting site called for line managers to be more supportive during a mother's pregnancy and when returning to work.
"It is sadly still far too common for women to feel shoved aside at work because they've decided to have children," said Clegg. "Aside from the obvious unfairness, it's also bad for our economy, which means everybody ends up losing out."
The study found almost half of mothers who fell pregnant were made to feel guilty by their manager, one in four felt their job was under threat, and more than one in three said they felt ignored when it came to career progression.
One anonymous respondent said: "I was deliberately pushed towards less financially rewarding roles as it was assumed I would not be interested in more challenging and lucrative roles any more."
Another said: "My job was given to someone else while I was on maternity leave, I was not made aware until I had my return to work interview."
Better work-life balance
Clegg praised the "many employers" who understood the importance of retaining the best staff by offering a better work-life balance.
Businesses that were regarded as family-friendly included Barclays, McDonald's, TalkTalk, BT, Pizza Express, Matalan and the National Trust.
"Modern families come in every thinkable shape and size," Clegg added. "In many cases mothers want to work and fathers want to spend more time at home. We need to dramatically update our working practices to accommodate these realities, helping families juggle their lives as they see fit," Clegg added.
Respondents said flexible working was the most useful thing employers could do to be more family friendly, with 28% of respondents citing it. Next most popular was emergency childcare provision (15%), followed by job shares (9%) and specific back to work programmes (8%).
Justine Roberts, Mumsnet, CEO, said: "Our survey reveals how important the culture created at work is. As members of our Family Friendly programme attest supporting women on their return to work improves retention rates and ultimately adds value to a company."
From April 2015, the coalition Government is introducing shared parental leave to ensure career options remain open to women after pregnancy.
