Between the networking, the interviewing, the negotiating, and the onboarding, moving on or up can feel like a job of its own.

Yvonne McNulty is a senior lecturer at the Singapore University of Social Sciences who specializes in expatriates and human resources. She has conducted extensive research on couples who move for one person’s job, and has noticed a recurring trend in the most successful of these relocations: the partner being offered the overseas assignment is a woman.

“I can count on my hand maybe one or two failures by women expatriates over the past 15 years in all the research I’ve done,” McNulty told Quartz At Work. “Women expatriates almost without exception handle relocations differently—and I would argue more successfully—than men.”

An employee’s performance at work may lead to a career-advancing overseas assignment, but it’s the situation at home that has the biggest impact on whether or not he or she succeeds in the role. Family reasons are the most-cited when overseas assignments don’t work out. Women, McNulty has observed, tend to do a better job of ensuring that their new job is a good deal for everybody in the household—both before and after the move.

Just as they do in their home countries, women working abroad continue to take on the lion’s share of a couple’s childcare and housework duties, even when they are the primary breadwinners, McNulty said. The decision to accept the overseas assignment is “an authentic joint decision; there is no bullying, no guilt trips, no ‘my career keeps you in the lifestyle you’ve become accustomed to’ nonsense to force a husband to say yes to the relocation,” she said.

Previous research has found that women tend to research job offers more thoroughly than men do. When it comes to international moves, if the arrangement isn’t a good deal for their partner—if the partner is reluctant to relocate to a new country, or will take an unwanted career hit as a result—women are inclined to forgo the assignment in the first place.

“If the husband is not 100% onboard, they turn the [relocation] down,” McNulty says. “No guilt trips, no nonsense. Women are smart that way.”

There are more women expats than ever before

Moving abroad for work can be great for a career. Two-thirds of the companies surveyed in Brookfield Global Relocation Services 2016 Global Mobility Trends Survey, an annual study covering 163 private sector companies with 11 million employees, said that employees who took international assignments were more likely to advance to leadership roles or to get speedier promotions and raises.

More women than ever before are being offered such roles. Responding companies reported that 25% of their people currently on overseas assignments are women, up from 13% in 1995.

The rise of dual-income families mean that more people—both men and women alike—are turning down relocation offers because of the impact on a partner’s career. Finding a job and securing work permits in a new country can be difficult for an accompanying partner (also known by the grim term “trailing spouse.”) A full 80% of partners aren’t employed during their spouse’s overseas posting. Most worked previously and gave up their jobs in order to follow their partner.

The survey didn’t note the gender of candidates who refused for family reasons. But 59% of companies surveyed said that female employees faced higher barriers to accepting international offers than male ones.

Perhaps one reason is that overseas assignments for straight, married women forces a reversal of societal relationship norms. “Now that a growing number of couples are seeing the woman succeed professionally at least as well, if not better than her partner, men are invited to play the supporter role. They have not been raised for this, and while some embrace it, others find it very difficult,” said Avivah Wittenberg-Cox, CEO of the consultancy firm 20-first, which specializes in gender and global companies. “Women are embracing their newfound roles and power outside of the home faster than men are embracing theirs inside of it.”

It’s a vicious cycle. When faced with a relocation offer, most dual-income couples choose to follow the job that offers the biggest salary or promotion, Wittenberg-Cox said, which advantages a partner who is older (in many heterosexual relationships, often the man) or works in a higher earning field (again—often the man, in partnerships where there is one). And while women give equal weight to financial and relational concerns when weighing a move, men tend to prioritize financial ones—where they often have the advantage.

“I see women engaging in healthy decision making when it’s their career for the relocation. I don’t see the same among men,” McNulty said. “By engaging in subsequent relocations (back to back) or by relocating when their wives are having babies and already out of the workforce, they deal their wives out of the relocation decision making because the wife no longer has a financial card to play.”

The repercussions extend beyond the confines of the family unit: 37% of companies in the Brookfield survey reported that the difficulty of recruiting female candidates for international assignments contributed to a gender imbalance at the management level.

Money + relationships + career

In the last two decades, companies have evolved in several ways that make it easier for men and women both to accept international opportunities, McNulty said. Women’s pay packages are approaching parity with men’s. Twenty years ago a male “trailing spouse” was virtually unheard of and companies offered little support; today, there are more resources on hand for employees and partners of all genders. Meanwhile, men who do take on the role of accompanying partner tend to be more proactive than women in seeking out work or projects that give them a sense of identity independent from the marriage, McNulty said, which leads to more satisfying relationships.

The barriers to parity, then, seem less a problem of human resources than of human relationships. When it comes time for those difficult moments of compromise and sacrifice, heterosexual couples too often end up weighing their choices, even unconsciously, on a scale tilted in favor of men’s careers.

The passage of time alone isn’t going to bring about equality. A 2014 study from Harvard Business School (paywall) found that only 26% of millennial women graduating with a Harvard MBA expected that a partner’s career would take precedence over their own—but a full 50% of their millennial male classmates believed their jobs would come before their spouses’. Someone there is going to be disappointed.

Fortunately, as an example of what things might look like in a better, more equitable future, we have the example of couples who have made successful moves overseas: men and women alike who have fully considered the costs and benefits for both themselves and their partners, and who can balance the commitments they’ve made to their families while forging their own careers and identity.

“Women expats look at it far more holistically in terms of money + relationships/family wellbeing + career,” McNulty said. “If one of those is off, they don’t do the relocation, because they know that success will only happen when all three are in place.”