If you're wondering why your last relationship didn't work out, or whether or not someone new is really a good match, one theory is that your birth order holds the answers. The idea is that when you were born -- whether first, last or in the middle -- helps dictate the type of partner you'll be. But can your birth order really have an effect on your relationship's success?

To learn more, we asked Wendy Walsh, a human behaviour expert and cohost of "The Doctors." She filled us in on five things to keep in mind about birth order and how it affects relationships.

1. Birth order stereotypes
When we look at a person's birth placement, it's common to make assumptions about the type of person they are. For example, being the oldest is often thought to mean the person is more selfish, dominant and prone to jealousy. "This makes sense because older children have more one-on-one time with family, so they would be more susceptible to jealousy," Walsh explains. But before you go labelling everyone you meet based on when they were born, get to know them first.

"The thing to remember is that birth order is a factor, but it is only one factor," she says. So, though it does play some role in how you and your partner will interact in a relationship, there are many other factors to consider.

2. Birth order and choosing a partner
Whether or not you realize it, the way you go about choosing potential partners can be affected by birth order. "I think birth order definitely has an influence in choosing partners, because we are always trying to replicate our early life relationships, even if they are bad, because we know that we can survive that," Walsh says.

So, for example, if you're a middle child with an older brother, you might seek out a partner who is the oldest in his family. We get so accustomed and attached to the roles we play in our families that we often seek relationships that will resume those roles, she explains.

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3. Relationship and birth order statistics
While there are many conflicting studies about birth order and what it means for relationships, one statistic stands out. "The only thing that seems to keep showing up over and over is not about what birth order works for successful relationships, but which birth order contributes to divorce," Walsh says.

Studies of failed relationships show that couples who divorce are most likely to have partners who are of the same birth order (for example, both partners are eldest children). This could be because they are simply too similar, she explains. If they are both the oldest, they might be used to babying and taking care of others, which causes conflict since those roles don't match each other's needs. Studies also find that a middle child is likely to be more faithful.

4. A better indicator of success
Rather than relying on birth order, a better indicator of how things with a new partner will go is what kind of relationship your significant other has with his mother. "A mother's love wires our brains for love," says Walsh.

To get a better idea of what you're dealing with, ask a potential mate about the kind of relationship he has with the woman who raised him. You want to avoid someone who feels the need to constantly call and check in with his mother, which can take away from his relationship with you, she explains. The other extreme (and potential red flag) is if he has a poor relationship with, or feels neglected by, his mother. What you want to find is a good balance. "Having a secure relationship with your parents will transfer to your relationship. You are looking for someone in between, who is a good, healthy version of an adult," says Walsh.

5. The key to relationship growth
Since many people subconsciously choose partners who will play roles in their lives that they are already comfortable with, rather than ones that challenge what they know, Walsh advises that it is important for couples to have some conflict. It's when you hit the hurdles that you have the chance to grow. "I always say a relationship is over when you stop growing," she says.

A lack of conflict may also mean two people have a lack of intimacy. "It's as if they're two happy roommates living together in the public areas of the house, not daring to tread on each other's tender spots," Walsh explains. This could mean the relationship will fizzle out rather than thrive.

Birth placement does have an effect on who we are as people, but it's not the only factor when it comes to the success or failure of a relationship.

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