"A baby changes everything." We hear that all the time and it's true, but not just in the obvious ways: less romantic time, fewer meals out, fewer books read, shorter workouts, less sleep... The shift to parenthood changes social networks: It pulls parents and siblings closer at the same time it shakes up friendships. And, all it takes is one baby, that first baby.

In doing research for my book Nobody's Baby Now a number of years ago, I found that even the most impossible adult child-parent relationships improve when a baby arrives. A grandbaby may be just what a parent needs to acknowledge a grown child's passage into adulthood. That passage allows both parties to relate on a more level playing field. Parenthood takes the onus off you and shifts the attention to your child. In highly fractious relationships with parents or brothers and sisters, that's a good thing. Strained sibling relationships can change for the better, too, as you bring a baby into the family. A new niece or nephew may be the one thing that you and a brother or sister has in common (other than your parents, of course) after years of disagreement.

Adjustments in your support network start during pregnancy; most adult women agree that the bond with their parents becomes even stronger after they give birth. Jessica, age 40, for example told me, "The birth of my daughter made me much closer with my mom. I was depressed and she came to help me. Her support solidified my vision of her as a great parent."

Danielle, 32, had a problematic relationship with her father until her son was born. "My relationship with dad has gotten so much better," she reports. "He has something else to focus on besides me and that's been positive."

Whether you conceived your child naturally or though a type of assisted reproduction technology, parents and siblings become more involved and supportive with a baby in the picture. In their 2010 article in the Journal of Family Psychology, "Social Nesting: Changes in Social Network and Support Across the Transition to Parenthood in Couples That Conceived Spontaneously or Through Assisted Reproductive Technologies," Sofia Gameiro and her coauthors looked at how your network and support system change during the third trimester and shortly after the birth of your first baby. They found that "..during the transition to parenthood new parents showed a strong nesting movement that consisted in drawing their nuclear family members toward them, from whom they perceived increased emotional and instrumental support."

At the same time, the transition to parenthood shakes up friendships. The withdrawal from social peers is logical and was noted particularly for mothers in Gameiro's study. New mothers, be conception natural or by assisted reproductive technology (ART) are busy adjusting to their parenting role and concentrating on their babies. But there are other explanations for ART mothers' reduction in their friendship circle as Gamerio points out: These mothers gave birth five to six years after their friends who are at a different stage and tend to be less supportive.

Similarly, childless friends have a different frame of reference and considerably more free time; they can feel neglected. After you have a child, it can appear as if you don't have much in common with friends without children-and some, although happy for you, may be jealous, divorcing, or experiencing infertility, all of which can affect your interaction. These friendships may have to be put aside temporarily. New mothers certainly don't have the luxury to idle away hours shopping on the weekend or to stop for drinks after work. Over time, key friendships can be re-instated or revitalized as children grow and interests shift. But, during pregnancy and caring for a newborn, parents and siblings take center stage in the social network, and for the most part, remain there.

The Baby Bonus

Tightening relationships with nuclear family is a baby bonus not usually articulated. Grandparents feel a genuine need to connect with their grandchildren. Parents who live long distances away are the first on an airplane to see (and help care for) the new baby. Many check in by phone regularly, if not daily, for years.

Siblings support also escalates. "My brother and I were always close, but the birth of my son made us closer," says 35-year-old Stella. "My brother and son [now age 5] have an amazing bond and that has been very helpful since my recent divorce."

The emotional support from nuclear family builds stronger ties to family and that can only improve the parenting environment and experience. In his book, The Secrets of Happy Families: Eight Keys to Building a Lifetime of Connection and Contentment, Scott Haltzman, notes, that "when the whole family pitches in together, they become a united team; they feel more cohesive and complete in their participation in the vital functions of the family as a whole. This is one of the big secrets of happy families: the tendrils of support and love extended to all members of the family."

And, all it takes is one baby, your first or only child.

How did relationships with your parents, siblings, and friends change when you had your first child?