While the birth order of both you and your spouse obviously does not determine everything that will happen in your marriage and the problems that you might have, birth order does play an important role in understanding how the two of you work together, how you might learn your difficulties and your weaknesses and your strengths.
Following are some of the potential combinations of birth order in a marriage, and what your potential difficulties might be and how the two of you might work together. Once again, everybody is unique, and so some, all, or none of these characteristics might apply to you. But understanding how your birth order affects you and how your spouse's birth order affects him or her can help you see your marriage more clearly.
Only child with only child. Generally speaking, if both of you are only children, you have a tendency to get along, but at the same time you live in two separate worlds. When the two of you are at home together, you might both be doing your own thing. There is little pressure on each other. You may find conflict in that you will probably expect the other person to understand what you are trying to say without you actually saying it. If both of you come from happy homes, then you will probably have a happier relationship, though if both of you grew up in a lonely home, then you might have trouble opening up to each other and really connecting.
First child with first child. First child with first child actually doesn't seem to happen particularly often. First born's seems to have difficulty connecting to each other, and tend to feel more of an obligation towards each other along with boredom and a sense of being out of touch with the other person.
First child with second child. A lot of the time, first born's are scared by second borns because they feel threatened by second born's in their own family. In the relationship, the first born is often psychologically threatened by the second born, and will be extra cautious around him or her because they are afraid of being offensive. However, the first born might find the danger posed by the second born to be attractive.
Second child with only child. This relationship actually is the most common marriage combination. The second born is usually drawn to the freedom of expression and freedom of emotion that is demonstrated by the only child, though that can start to be a little bit irritating. The only child usually is also talkative and highly organized.
Second child with second child. Seconds work well with each other because both people tend towards perfectionism and these qualities reinforce each other. This relationship probably would not be particularly emotionally challenging, and actually mind end up minimizing emotions.
Third born with third born. Third born's end up working well together, because they both work hard to make the other person happy, they both work to understand each other, and they overlook the eccentricities of the other person. Difficulties might come up if one or both people end up bringing children into the relationship, because they will tend to be defensive of the children.
There are a number of other possibilities, obviously. But generally speaking, it is helpful to look at the other person's situation in their family and how they relate to their siblings, if they have any. It is also good to understand yourself and how you relate to and are affected by your position in your family.