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Childcare commitments are the most frequently cited factor for women leaving Big Law, according to a survey of more than 1,200 senior partners by ALM Intelligence and the American Bar Association.

In "Walking Out the Door: The Fact, Figures, and Future of Experienced Women Lawyers in Private Practice," about 58% of women respondents cited caretaking duties as an "important influence on women leaving their firms."

Perhaps more strikingly, the study highlights a significant gender gap in childcare responsibilities. While 54% of women respondents said that arranging childcare is their full responsibility, only 1% of men said the same. And while 34% of women attorneys say they are the only parent to leave work for childcare, the responsibility falls on just 4% of men.

This dichotomy perfectly illustrates why many women leave Big Law, said Michelle Browning Coughlin, a partner at Kentucky-based Wyatt Tarrant & Combs and founder of MothersEsquire. Childcare alone isn't the reason why women leave, she said, but the combination of having to manage professional obligations with the near-sole responsibility of raising a child is a huge factor.

The countless hours it takes to be the primary caregiver of a child eats away at professional responsibilities, many of which are listed as other major factors for why women leave firms: stress levels (54%), emphasis on marketing and origination (51%) and the number of billable hours (50%).

The study's authors called this phenomenon "Death by a thousand cuts."

"Mothers hear it all the time: Aren't you going to volunteer for the church picnic? Aren't you going to help plan the women's retreat? Aren't you going to bill 1,900 hours? Your daughter got a C on her latest science test, are you helping her out enough?" Coughlin said.

Thus women are often given a binary choice between a successful legal career and raising their children—a decision men rarely face, according to the data. More often than not, women choose their children.

"What I hear from my clients, is 'Ok, you can stay home, but you still need to bill,'" said Elena Deutsch, founder of Women Interested in Leaving (Big) Law, or WILL. "I had a client who had a child and was on bed rest and was still asked to bill. The standards for women are the same, if not higher in some cases than men. Women have all these extra responsibilities."

The study put forward a few solutions, including adding on-site childcare as one of the so-called concierge services many firms provide. Outside of revamping U.S. cultural norms, Coughlin said that firms need to deemphasize the billable hour in favor of a flat fee and include simple quality-of-life improvements such as breastfeeding accommodations in firms and legal conferences.

Kristen Riemenschneider, a mother of three and a newly minted equity partner at Arnold & Porter Kaye Scholer, said her success as a mom and Big Law partner boils down to one major factor: flexibility.

Riemenschneider has worked on a part-time schedule since her time as a junior associate, and currently bills on an 80% schedule. While her children were young, she left at 3:30 p.m. each day and got back online at 8 p.m.

"Had it not been for an incredibly supportive group of partners, I would have left," she said.

Riemenschneider's husband also made it clear to his coworkers that if she was unavailable in the case of their child's sudden illness he would have to leave—a dynamic that allowed her more flexibility and something she would like to see replicated.

"There needs to be greater normalization in a firm around 'yes, a father should be able to leave around 4:30 to take his child to soccer practice,'" she said. "It's a bigger problem in society that women are expected to bake the cupcakes for the bake sale or pick up the soccer uniforms. Leaders need to say that they understand that a dad needs to be available for their child."

Most law firms offer parental leave, with policies ranging from 10 to 22 weeks. But diversity experts say there's often a greater stigma on heterosexual men going on parental leave, and men are rarely offered the full length of leave, with some getting as few as two weeks or no time at all.

For Riemenschneider, offering flexibility isn't just a parental issue. After all, not everybody wants children, and many who don't have children grow to resent mothers who can't work on weekends, for example. But firms would retain more attorneys if their lawyers were given more flexibility in all aspects of their career, like going on vacation or taking care of an ailing parent, she said—a sentiment legal talent experts agree on.

"There's an emphasis on child or no child," said Riemenschneider. "But it should be about being human and life happens and helping each other out."

Read More:

'Death by a Thousand Cuts': Why Are Women Leaving Big Law?

Are Parental Leave Policies Innovative or Just Expected Now?