Dr. Kevin Leman weighs in on birth order and how it affects your kids' personalities and professions.

With the recent news of actress Cate Blanchett giving birth to her third son, momlogic asked parenting expert and author Dr. Kevin Leman for his take on how same sex birth order can determine your child's personality and career prospects.

Having same sex kids heightens competition and sibling rivalry. With three boys, it ensures that the first and second born are going to be night and day different--heightened competition and rivalry within the children. The first one is conservative, and they don't like surprises. That little tag in back of the shirt or blouse drives the kid up the wall. There are streaks of perfectionism in first born children. Astronauts, surgeons, CEOs, pastors, rabbis are traditionally first born children. Twenty-one of the first 23 presidents were first-born children. Plus, Hillary Clinton is first born, and Barack Obama is as well.

The middle child is full of antics. Middle children rebel and do things differently than their older siblings. They are typically mavericks and mediators who are most likely to become entrepreneurs like Donald Trump and Bill Gates.

Babies go way out of their way to take a different path. The youngest child uses humor, they're good on their feet, and they tend to be babied. Babies of the family are manipulative, outgoing, and do extremely well at sales. They could sell rats for a living. Some famous babies of the family include: Steve Carell, Billy Crystal, Eddie Murphy, Drew Carey, Steve Martin, Ellen Degeneres, and Jon Stewart, among others.

A parent will identify with a child who is in the same birth order as they were. If Cate's husband is a first born male - he's going to over-identify with the first born male. If Cate is a middle child, she may over-identify with the middle son in the family and be more protective of him because she knew what it was like to grow up as a middle child.

As more children come into the birth order, parents lighten up. If Mom and Dad are in the park with their first born and he picks up a foreign substance, they want to call 911 or swab out the baby's mouth. With a baby in the family six years later, the child picks up a cigarette butt complete with filter, chews it and swallows it, the husband looks at the wife and says, "Good roughage, good roughage. Don't worry about it."

Marriage and birth order: A first-born daughter in a family becomes the nurturer and tends to be a pleaser. Your first-born son, on the other hand, tends to be a controller. Ironically, pleasers typically marry controllers, but the best marital matches are when you go outside of your birth order. I'm married to Mrs. Uppington - she's a bossy first-born who takes great pleasure in telling me what to do, and yet we've been married forever and have a great marriage. I have a little reality in my life.

Dr. Kevin Leman is the author of the new book, Have a New Kid by Friday and the best-seller The Birth Order Book, among many others. His next book, The Firstborn Advantage, will be released by Revell Books this fall.