Editor's Note: (Kelly Wallace is CNN's digital correspondent and editor-at-large covering family, career and life. Read her other columns and follow her reports at CNN Parents and on Twitter @kellywallacetv.)
(CNN) On my first day back at work as a network news correspondent after my first child was born 11 years ago, a late assignment meant I arrived home long after my daughter had gone to bed.
A few mornings later, the phone rang as I got ready for work. My boss said I needed to travel to Massachusetts to cover a story. I hung up and burst into tears.
My husband tried to make me feel better, saying I would be on the national news that evening, but all l could think about was being away from my daughter.
My re-entry to the work world was anything but easy and seamless. Before I gave birth, I thought I'd return to my hard-charging television correspondent role three months after delivery and pick up exactly where I left off.
And then I held my baby and couldn't imagine leaving her for an hour to get a haircut, let alone 12 hours, which is the time I typically logged each day at work before I became a mom.
I struggled with a changing identity and balancing the demands of motherhood with the challenges of a network role. Why hadn't anyone told me how hard it was going to be -- or was it just me? So many other women seemed to be handling things much better.
If only I had known then that what I was going through was the "fifth trimester," a term coined and trademarked by author Lauren Smith Brody, a former executive editor of Glamour magazine and a mother of two.
We mark pregnancy in three trimesters, and the "fourth trimester" is used to mean that time after delivery when your baby is adjusting to life outside the womb.
The "fifth trimester"? It's the time when new mothers, just months after delivery, are going back to work but often before they feel emotionally and physically ready to return, said Brody, author of the new book "The Fifth Trimester: The Working Mom's Guide to Style, Success, Sanity, and Big Success After Baby."
Brody considers the "fifth trimester" to be the first few months back at work, whether women return after a week or after six months of leave, whether they work in blue collar or white collar professions, whether they have paid leave, or are like the majority of Americans who work at companies that don't offer any paid leave. (The United States is the only industrialized nation that does not mandate paid maternity leave.)
"For the first three trimesters, you could fill bookshelves full with the number of books out there, and then the same actually when (my son) was born, there was the fourth trimester, which was a term that was new to me at the time," she said. She was helped along by books about re-creating the womb during those first months after her son was born.
"But then I got back to work, and I had this weird feeling of both, 'Oh, thank goodness, I know how to do this,' and then also, 'Oh, no, I really don't know how to do this with a baby,' and there were very few resources to help me ease back in and to help me manage my expectations of myself and not blame myself for it being such a struggle."
Brody, whose sons are now 5 and 8, said she remembers feeling so harried when she returned to work that she didn't even take the time to look around to see whether any resources might be available for her. She realized later that she had undiagnosed postpartum anxiety after her first child was born.
"I hated that I wasn't what I expected of myself," she said. "And that after all these years of achieving at work ... here I was with a baby, just absolutely incapacitated, and I was so thrown by that and so disappointed in myself."
The veteran women's magazine editor was open with her colleagues about her struggles in returning to work. As her sons got older, she found herself offering advice to women in the office who were starting families. And then, as she started thinking about what she might want to do next in her career, she wrote a memo of story ideas. The concept of promoting the "fifth trimester" was one of the ideas on her list.
"It was really, really eating at me," she said. "I felt this sisterhood of mentorship and this working-mom mentor thing was really needed and real. And I knew that my experience alone is not enough to help everyone in the world, my God, definitely not. But if I could collect this huge breadth of experiences and put them all together and offer people that working-mom mentor that I didn't really feel like I had, that would be really valuable."
She put together a 50-question survey and sent it via email to people within her network, asking that they also share it socially and with their respective networks of family, friends and colleagues.
She hoped for 100 responses but ended up with more than 700, representing working women from every state in the country and from a range of professions, including police officers, teachers, doctors, lawyers, Fortune 500 executives, business owners, waitresses and freelancers. She followed up with more than 100 of the women, conducting in-depth interviews with them that help form the basis of her book.
"It was amazing to see the differences in their experiences, but what I actually found more remarkable was sort of the emotional through line of the things they had in common," Brody said. "Everybody talked about guilt, even if it meant a different thing to each person. Everyone talked about coming back to work, feeling different and knowing that people saw them differently, no matter what field they were in."
Seventy-five percent of the women Brody surveyed said they wished they had been able to take a longer maternity leave. When asked how much extra time they would want, the most common answer was "a few more months," according to the book. This response tracks with what Brody heard from the women in terms of when they felt physically and emotionally back to normal after giving birth: The average respondent said they were physically back 5½ months after delivery and emotionally back after almost six months.
Brody interviewed women who returned to work a week after delivery and others who had six months of leave. "Either way, there's a monumental transition," she said. "I like to point out that the fifth trimester might be longer for some women and shorter for others. You kind of don't know how long that transition time is going to be until you're on the other side of it ... I will say that when women went back very, very early, they seemed to have lengthier transitions."
Brody's survey is not scientific, she admits, but it does reflect some of the major stresses new mothers experience when they return to work. Even if a woman is able to take the three months of unpaid leave required in the United States under federal law in most cases (companies with fewer than 50 employees are exempt), she is still returning months before she feels emotionally and physically back -- and months before she is getting a decent night's sleep. The typical baby in Brody's survey was sleeping through the night at just over 7 months old.
When you add in the stresses on a relationship, you've got what Brody aptly describes as a "mess." Seventy-one percent of women said they battled more with their partners in the first three months after returning to work than they had ever before. It was the most stressful time in their relationship, they said, even more stressful than adjusting to a newborn or the first year of marriage.
So what's a new working mother to do? Brody, who is a passionate advocate of paid leave, uses her book to focus less on what companies can and should do to help women with re-entry, and more on what women themselves can do. She provides tangible tips and helpful advice from women who have been there and who more than survived, they thrived. She covers such issues as "how to win over any resentful colleagues" and preparing for that first day back at work, which she calls the "second cutting of the cord."
She encourages women to get their child care up and running slightly before the first day so they can try it out and adjust to leaving their loved one in the hands of someone else.
She's proudest of a chapter on the importance of emotional health titled "On Feeling Human Again" and says the simplest way to feel very good again is to ask, "What do I need right now?" Think about what you need -- at home and at work -- and ask for it, she said.
About one in seven women will have a postpartum mood or anxiety disorder, according to the American College of Obstetricians and Gynecologists. Her risk increases if she is facing any kind of extenuating circumstance, such as single motherhood, loss of a job or a big life transition, according to Brody.
Going back to work sooner than you are ready can be an extenuating circumstance, she believes. One study found that the risk of postpartum depression was higher in women who took maternity leaves of less than six months.
"This is a matter of moms feeling like, from the very beginning, they can ask for what they need," she said. "If you don't ask for what you need, you will find yourself in a deeper and deeper hole to dig yourself out of."
Brody has also created a business called The Fifth Trimester, which works with new parents and companies to create more family-friendly cultures in the workplace. In addition to working with companies on ways to invest in women once they come back from work, she spends a lot of the time in her workshops talking about those "soft skills" that can help new mothers get what they need, whether it's at work or at home.
She points to unique approaches some companies are taking, such as home furnishings firm Wayfair, where conversations begin about how employees want their jobs to transition even before they go on leave.
"They are so forward-thinking in this stuff, and they have just completely made it the norm that whenever someone is at the point where they announce a pregnancy or that their partner is going to have a baby, the conversation is completely opened up: 'How do you want your job to change and evolve?' " Brody said. " 'It is just an assumption that you're probably going to want to, so let's talk about it,' and then it becomes an opportunity, and this is something that I think a lot of companies of any size could do."
She also points to how women can feel good about their skill set when they are back at work. New mothers are much more decisive about what they say "no" to -- they are making calculations about what comes at the expense of time with their child.
"But the things you say 'yes' to, like that new project you're taking on, you are so committed to it, because you've done the math on it, you've done the kind of emotional math on it to figure out, 'what am I going to feel from what compromises I'm making in order to be able to really commit to this?' So when you do commit, like, you are all in, and I think that's an amazingly valuable approach that women have when they come back to work and quality that they have when they come back to work."
As more parents and companies start talking about the "fifth trimester," Brody hopes people will come to understand that this transitional time exists and presents a host of challenges but also that women can get through it and come out stronger in every way.
"For me, I found that it was really helpful also to understand that the transition was finite and that when I got to the other side of it, I would actually see, really clearly see all of the ways in which I was a better editor, a better employee, a better manager and leader."
For any women who are adjusting to the return to work or who have gone through it, Brody hopes they'll be open about their experiences. She says she wants every woman to do what works for them emotionally but hopes they realize that the more open they are, the better off we'll all be.
"If you are just open about what is challenging in this transition, about the fact that it is probably too soon (to return to work) if you feel that way, but then also about the fact that look at this, you are still getting your job done ... and even the things you're struggling through, you're going to get through it, look back and see that you made it through and came out stronger," she said.
"I hope the book gives new moms the courage to be honest and open about the challenges of new working motherhood, so that even when you're struggling, you are doing a greater good by educating your workplace -- and shifting workplace culture for the better.
"More than anything, it's important to be transparent about the challenges but also about the triumphs. ... That will also help everyone be less afraid of it, both of going through it and managing people who are going through it."