These children tend to be conscientious, ambitious, organized and—in relationships—dominant. Firstborns like to be in control. As with all birth-order positions, gender plays a role, too. In the case of firsts, oldest sons tend to be take-charge types, leaders. Oldest females, on the other hand, are more likely to be bossy, confident and aggressive than their younger sisters.
Middle children are the least defined of the types (there can only be one eldest and one baby, but middles shift depending on how many there are in the whole family). That said, they can be predictable in the best sense of that word. Middle children are the Type O blood of relationships: They go with anyone. As a general rule, middles tend to be good at compromise—a skill valuable to them as they negotiated between bossy older sibs and needy younger ones. However, some middle children (probably for the same reasons as above) can be secretive
Ah, the little sibs of the family. Beloved, treasured, and in many cases babied for much longer than their older siblings (and often by their older siblings), the stereotypical youngest of the brood tends to be less responsible and more devil-may-care, with less of a hankering to take charge. That can be different if the baby of the family came after a gap of more than a few years, though. In that case, the baby of the family may act more like an only child or an older sibling—as though the family had started all over again.
The stereotype about only children is that they are pampered and precious, and thus will have trouble ceding the spotlight to anyone. But that doesn’t describe every only child. In fact, many onlies act a lot like firstborns. They tend to be responsible as well as mature. In fact, many “grow up” more quickly than kids with sibs, thanks to how much time they spend with adults.
Oldest with Oldest
Can you say Bill and Hillary Clinton? The ultimate political power couple, two firstborns, is a classic combination of control, dominance and striving. Two firstborns often butt heads because both want to be in control of every situation. They may fight over what movie to see, how to raise the children, where to live. All relationships have these issues, of course, but these two strong personalities, used to getting their own way, may feel them more intensely. Relationship Tip: Try to understand that as strongly as you feel about something (like where to go on vacation), that’s likely how strongly your partner feels about his choice. Take that into consideration and make compromises to keep the relationship solid.
Oldest with Middle
This can be a fine pairing most of the time, but the middle child’s tendency to mold herself around her partner may leave her in danger of not following her own dreams. Of course, a lot depends on how domineering the firstborn partner is, and how “classic” the middle child’s accommodating personality is. Remember, such variables as gender and age spacing play a role in how close your personality hews to the birth-order line. A middle child with close-in-age older and younger siblings is more “middle-ish” than one whose younger or older sibs are years apart. Relationship Tip: If you’re the middle child, use your natural ability to compromise to decide what you’re cool with leaving to your capable firstborn spouse, and what you’d prefer to control. Then break out of your natural tendency to let things go, and speak up!
Oldest with Youngest
This pairing has some good mojo behind it: The youngest child is cared for, while the older sibling can exert control. The baby of the family tends to be the type who needs attention; the firstborn, who was alone for a while in the family, doesn’t need to seek attention, because he or she usually got it. Relationship Tip: Emphasize the relative strengths of your personalities. If you’re married to a lastborn, don’t disparage what you see as his lack of responsibility. Instead, go with him on some adventures. Conversely, if you’re a lastborn married to an oldest child, you can learn how and why being serious can be a good idea.
Middle with Middle
Too bad Jan and Peter Brady couldn’t marry! Their smack-in-the-center, sensitive, compromising natures would have given them an edge in keeping a relationship healthy. In studies of marital satisfaction, middle children fare best all around. Even so, if both of you tend to be the secretive type, you could have difficulty communicating. Relationship Tip: Have frequent, air-clearing conversations about everything from money and sex to the kids, home and work so your individual needs don’t get drowned in a sea of compromise.
Youngest with Middle
While as a rule, middles can usually have harmonious relationships with someone from any birth order, this combo may present some issues. That’s because middles morph into the styles of the other types, depending on the dynamics of their particular family. A middle child with a much younger sib may act more like a lastborn (and the opposite situation may make the middle more like a firstborn). Relationship Tip: Try to figure out whether you have controlling tendencies (which you should keep in check so you don’t overwhelm your younger-sib spouse) or if you both are acting like “babies.”
Youngest with Youngest
These two can have a lot of fun—a pair of carefree, risk-taking lovers nearly always do. But the classic conundrum here is that no one wants to be in charge. You may find that neither of you wants to handle the finances or make other important decisions. Two last-born parents could be in a tough position: Both may prefer to be the kids’ friend, not the heavy hand when it comes to discipline, which puts a strain on a marriage. Relationship Tip: Try to figure out which of you is best at certain tasks (such as handling money or making decisions about the children), and then own up to that responsibility, rather than assuming the other will take care of it.
Onlies with Anyone
Unlike the other birth-order positions, only children haven’t been studied as much. Most people assume an only child will resemble a firstborn in relationships, since they are, after all, first, but that doesn’t take into account the fact that an only never had an advisory (or bossy!) role with younger sibs. An only with a firstborn can be a good match if the only child acts less classically “firstborn.” And an only with the lastborn can present issues, if the only has had little experience with the relatively immature, attention-seeking behavior of the baby of the family. Perhaps no surprise, middles and onlies make a good match, with the middle child accustomed to the needy side as well as the possibly bossy side, of his or her “only” love. Relationship Tip: If you’re with an only, figuring out whether he’s more like an autocratic first born, or a pampered lastborn, will help you work through relationship snafus more smoothly. And if you are an only, you may do well seeking out a partner of any birth order who has a clutch of siblings, if you were the type who always missed siblings in your own home.
Resource: Woman's Day