A friend of mine, the mother of six, just had a job interview. While she didn't try to hide the fact that she had children, she also wasn't planning to share that she had six of them. So, imagine her surprise when one of the interviewers said, "So you have six children. I've just read your CV and it was on there."

It wasn't. She believes the interviewer found out by speaking with a friend of hers who worked for the same company or by looking at her Facebook page. She has her privacy settings at an appropriate level, but her cover photo was a family picture--complete with all six children.

Her husband has a similar picture as his cover photo--albeit with five kids (pre-latest baby). He's never, ever, not once been asked about family size in a job interview. And why should he? It's not part of doing the job. It wasn't part of the job my friend applied for either, though, so why ask?

Katherine Goldstein recently published an op-ed in The New York Times that asks about anti-mom bias and why it's so prevalent. She writes:

"In recent months, we've seen a flood of stories about sexual harassment and gender discrimination in the workplace. But the struggles of mothers specifically have been largely left out of the spotlight -- even though, as in my conversation with this woman, the bias against them is often casual, open, and unapologetic."

But Goldstein references a conversation where she viewed this bias firsthand, and it actually makes the issue more complicated than it seems on its face. Here's the conversation as she wrote it:

"Last fall, I was in a meeting with a leader in women's health, discussing re-entry-to-work programs for new mothers when, out of the blue, she began complaining about a former employee. This employee on their small team had gotten pregnant, the woman said -- and it was a problem: "She was way too focused on her pregnancy. It was distracting her. I didn't think she was going to be committed enough to the job, so I had to let her go.""

Here's the problem with claiming bias and discrimination: what if this is the truth?

What if all this newly pregnant employee could talk about was the pregnancy and the expected baby? What if she was no longer working hard? Should a company be required to not only give maternity leave but allow an employee to slack off for the nine months prior to the birth? Of course not.

We don't know the extent of the conversations this manager had with her pregnant employee. If she just said, "Ahh, you're pregnant, you're no longer career-focused, you're fired," that is a blatant act of illegal discrimination. But if the employee had lost all focus and the manager had numerous conversations with her, put her on a performance improvement plan, saw no improvement, and then terminated her, it would be justified.

While it's absolutely critical we consider each and every employee (and job candidate) as an individual and do not make assumptions based on stereotypes, we can't deny that women who have children behave differently than women without children, and differently than men.

According to Claudia Goldin, a professor of economics at Harvard University, women prefer what she called "temporal flexibility." Goldin believes this choice explains much of the gender pay gap. Joan C. Williams writes in the Harvard Business Review that only 13.9 percent of college-educated women work more than 50 hours per week between the ages of 25 to 44, which are considered the key career-building years. On the other hand, 29 percent of fathers who live with their children work more than 50 hours per week.

Williams draws this conclusion: 

"This 'long-hours problem,' analyzed so insightfully by Robin Ely and Irene Padavic, is a key reason why the percentage of women in top jobs has stalled at about 14 percent, a number that has barely budged in the past decade. We can't expect progress when the fast track that leads to top jobs requires a time commitment that excludes most mothers -- and by extension, most women.

Now, you can argue up one side and down the other that we should change the paradigm so long hours aren't necessary to rise to the top. But that doesn't change personal preference, and it makes little sense that we should treat someone who devotes an entire life to the business the same as someone who wants to work part-time. While Gladwell's 10,000-hour rule isn't perfect, the principle is solid--if you do more work, you understand better how to do the work. 

Women, according to a 2013 Pew study, want to work part-time at far higher rates than men--almost 50 percent of women say this is the ideal situation for women with children under 18.

In Denmark, where maternity and paternity benefits are generous, mothers and fathers have a combined leave of 52 weeks--a full year. Moms are guaranteed 18 of those weeks, dads 2 weeks, but the remaining leave can be split any way the parents want to. Moms take 92.8 percent of that leave.

So, while every instance of discrimination against moms should be investigated, we can't assume that differences happen because of discrimination. 

You should never ask a job candidate--male or female--about their offspring in a job interview. You should never assume that childcare duties will be carried out by mom. Never make an assumption, one way or the other, about what a woman will do after having a baby. The study that indicated moms were 37 percent less likely to be hired than non-moms is horrifying, and companies should make sure they don't discriminate in this way. 

But remember, unequal outcomes don't always point to discrimination. Choice plays a tremendous role in how women approach their careers, as it does for men.