In Hindu Tradition, while getting married you make 7 Vachan(promise) to your better half. You also promoise to spend 7 Janam(Birth) with them. My interpretation of 7 Birth is not literal birth, but what our ancestors wanted to say was that 7 Birth is equivalent to 7 drastically different stages of both of your new world which starts the day you got married.
First one being married itself, you will be living together now onward, you woll be sharing not only life but also your room. Your life before marriage is a very new phase. Person you had spent brief amount of time during the day will be there. When we meet for some time we are on our best behaviour but when we live together that's when we get to know about each other in depth. This change of a second person entering your inner part of life is a new birth.
Second I believe is the birth of a child. Till now it was just the two of you young, slightly mature but the decisions that were being taken was only for both of you and the repercussions of those decisions were also for both of you only. But now that is going to change there is a tiny little human being for which two of you are primary and that little sunshine becomes your primary. For the first time in life you both there is a common someone which is above yourself.
Third is when the child start going to school. When you 24X7 revolves around your baby and then they start going to school and suddenly you and your partner found yourself with new free time slot of half day. Tiny little being that was fully depended on you, has started going out in the world with less dependence on you.
Fourth is when the teenager leaves the home for the college, for more than one and half decade later, your young one will leave the house and for the first time since his/her birth you and your partner will have the house for yourself.
Fifth when they get their first job, they finally move beyond the walls of home/school/college and into the world and get to know the chaos and positivity and negativity and the reality. How both of you help them understand this drastic non dependent behavior to the young brain
Sixth is the Marriage of you child. they are starting their own new world. You are getting another person in your life sharing the life of your child with them. Going to be a new adjustment for you both
Seventh a new addition to the family, this is the one that you will enjoy the most. Your child bringing a new child in the world and the whole circle goes on.