According to Washington research group Child Trends, unmarried motherhood is becoming increasingly common in the United States, especially among younger women. In fact, as of 2012, a majority of American moms under 30 years old hadn't walked down the wedding aisle.

During the late 1700s and early 1800s, republican motherhood caught on to promote child rearing as a way to raise up a generation of virtuous citizens in the fledgling United States.

In 2011, the U.S. teen birth rate dropped to its lowest rate since the National Center for Health Statistics began tracking the data, down from a high of 61.8 teen births per 1,000 in 1991.

Feminist poet Adrienne Rich wrote the profound statement about the elusive nature of motherhood in her 1976 book "Of Woman Born: Motherhood as Experience and Institution."

Both staying at home full time and working full time present psychological challenges for mothers either struggling to find autonomy outside of their domestic identities or carve out more time with children in busy office schedules. At the same time, research indicates part-time employed mothers are the least stressed and most satisfied with their family life.

Many pregnant women and new mothers report a phenomenon called "mommy brain," which is typified by spotty short-term memory that leaves them forgetful and easily distracted.

According to the U.S. Department of Health & Human Services, mothers who relinquish their babies for adoption are a statistical rarity in the United States, with only 14,000 doing so in 2004.

According to data from the U.S. Census Bureau, the average age of new moms in the United States in 2009 was 25.1 years old.

Moms toting around M.B.A.s may receive the biggest punch to their paychecks. A 2010 Harvard study found that business-oriented working moms experience a 41 percent income disparity, compared to their male coworkers. Medical doctors get the lowest "mommy income penalty."

Repeated studies have confirmed what many parents can probably tell you: Starting a family takes a toll on a relationship. On average, couples are happier in empty nests, both before and after raising children.

After childbirth, mothers experience neuron growth in the olfactory (smell) center of their brains. This helps them detect the scent of their babies and assists with the intensive process of mother-newborn bonding.

By 1960, nearly a third of American mothers worked outside the home, despite that period's popular portrayal as the era of the full-time housewife.

Becoming a mother can take a bite out of a woman's paycheck. According to data from the National Bureau of Economic Research, highly skilled women give up about 21 percent of their lifetime earnings in exchange for having kids.

Not surprisingly, getting a rid of a baby in one's belly also gets rid of some pounds. According to the U.S. Department of Health and Human Services, the average new mom immediately drops 10 pounds (4.5 kilograms) during childbirth.

The "baby blues" and their attendant mood swings are a common side effect of new motherhood, likely caused by major postnatal hormonal shifts. Postpartum depression is a more serious and persistent mental health condition that generally develops a few months after delivering.

Being a housewife in the 1960s was a full-time job and then some; data show that the average June Cleaver put in 55 hours per week keeping her home spic 'n' span.

Breastfeeding mothers commonly complain of lackluster libidos, probably due to hormones. Lactation-inducing prolaction and the act of breastfeeding simultaneously diminish levels of estrogen and testosterone that promote healthy sex drives. Typically, after a child weans, libido comes back as well.

Scientists have found that new mothers' brains undergo neuron growth in the prefrontal cortex, likely preparing them for the 18-year multitasking responsibility that is raising a child.

Psychological research out of Kansas State University has found that men tend to experience "baby fever," more commonly after they have their first child, whereas women tend to experience it more dramatically before giving birth for the first time.

According to research out of Finland, a majority of adult men come down with a case of "baby fever" at some point, with about 58 percent reporting having experienced the sudden, overwhelming urge to have a child. It's more common among women, with 78 percent catching "baby fever," most typically during their late 20s.