Couples spend the first 5 to 10 years of their marriage butting heads over how their family should work, says Dr. Robbins.
"People often don't realize that they come into a marriage with an idea of how a family works based on their own family -- whether they liked them or not," he adds.
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You can end up fighting over something as trivial as how you should hang your toilet paper, but those little issues can add up to big problems, particularly if children enter the picture. A 2004 study found that how a couple manages parenting responsibilities when the child is an infant is associated with the quality of their marriage two-and-a-half years later.
You and your partner may have vastly different ideas about how a child should be cared for and what constitutes family together time. If one of you is working, should the other partner get up with the baby at night, or should you take turns? Is it important for you to sit down to dinner as a family every night? "You need to figure out how you can live together happily while each maintaining your own sense of self," says Dr. Robbins.
4. Make sex a priority -- but not a chore
While you should make sex a priority, you shouldn't pencil it in on your planner. If you schedule sex, it becomes a responsibility --just like taking out the trash, says Andrew Goldstein, M.D., an obstetrician and gynecologist at the Johns Hopkins School of Medicine, in Baltimore, and the coauthor of "Reclaiming Desire."
The average married couple has sex 58 times per year, or slightly more than once a week. And a recent eight-year study found that 90 percent of couples experienced a decrease in marital satisfaction after the birth of their first child.
But it doesn't matter whether you're having sex five times a week or five times a year -- as long as both of you are happy, says Dr. Goldstein. In fact, a 2008 study found that couples who reported any kind of marital intimacy -- everything from holding hands to sex -- exhibited lower levels of a hormone produced by stress.
5. Be flexible
Whatever financial and household arrangements you agreed to in your 20s or 30s, chances are they're going to change at some point in your marriage. Men account for 82 percent of recent job losses during this recession, meaning couples are making some hard choices when it comes to both their careers and their checking accounts.
If the traditional breadwinner is laid off, the stay-at-home parent may need to head back into the workforce. Conversely, if you become a stay-at-home partner -- due to choice or circumstance -- expect to do more of the shopping, cleaning, and other chores that make a household run smoothly. A recent analysis of government data found that employed women spend significantly more time on child care and housework than employed men -- and unemployed men.
Having an open discussion of how household duties need to change can help couples weather some tough transitions. "Everyone has a role within the relationship and as long as there's a greater good, it's not a question about whether it's his money or her money," says Dr. Goldstein. "It's their money. Your paycheck and your career are not the value of your worth."
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6. Stay active as you age