Ever wonder if birth order affects your relationship? I consulted William Cane, author of The Birth Order Book of Love: How the #1 Personality Predictor Can Help You Find The One, to find out which relationships work the best. Cane explained our best matches like this:
Female oldest child: The firstborn girl will usually have a leadership streak, so she’ll be happy with a last born. (That’s based on the pop-psychology view that opposites attract, he notes, although the research behind that isn’t conclusive.) A firstborn girl with younger brothers will be happiest with a last born guy with older sisters.

Female middle child: She is more adaptable than first or last. The middle child grew up with both older and younger, and can relate to all. She has the most potential for making a good match with anyone. And yes, middle borns are often neglected—statistically, they receive 12 percent less attention from their parents than their siblings. But the gender of her siblings is important. Britney Spears has an older brother and a younger sister. The important thing for her is her opposite sex sibling. She would be best with an older brother who has a younger sister or two younger sisters.

Female youngest child: The last born can be happiest with the firstborn, especially if she has an older brother, and she’ll be happier with a firstborn with a younger sister.

Female only child: If she’s going out with a firstborn, she’ll be used to an older authority figure because she grew up with her parents. She will understand the firstborn male, especially if he has younger sisters.

A twin: Your parents MAY call you a firstborn, but it’s a negligible effect. The best match for a twin is another twin or someone with a sibling very close in age.