When she was pregnant, Ashley Grover Desmarais did not give much thought to vaccinating her child.

It hadn't occurred to her that she could do anything "out of the norm" until late in her pregnancy, when a friend posted on Facebook the reasons why her daughter was unvaccinated.

The post prompted her to do some research. Grover Desmarais, 30, discussed vaccination with her pediatrician, other friends and family, and read various books and articles on the subject. Ultimately, she settled on an augmented schedule: Her daughter, who will be 3 in June, and her son, almost 1, will be fully vaccinated by the time they're school age, but they are following a delayed timeline.

"Many of my other friends have also done augmented schedules for their children's vaccinations," said Grover Desmarais. "I think it's because there's more awareness, more research available, and we're all able to post our findings and experiences on social media."

Despite clear support from major medical groups in the United States, some parents grapple with whether to vaccinate their children according to the immunization schedule recommended by the Centers for Disease Control and Prevention. A new study, among the first to probe the social factors that affect parents' decisions, found that friends, family and health care providers play a huge role in what parents choose.

Researchers surveyed 196 first-time parents about who they discussed vaccination with, as well as the types of sources they consulted, including books, media outlets or research articles. One hundred twenty-six followed the nationally recommended vaccination schedule, and 70 did not. (The study, published in the journal Pediatrics on Monday, was based in Washington, a state that has one of lowest vaccination rates in the U.S.)

Nearly all the parents indicated they had what the researchers called "people networks" -- groups of individuals whom they consulted about vaccination. Parents who decided to delay vaccinations, who opted for only some vaccinations, or who decided against vaccination -- dubbed "non-conformers" -- tended to have slightly larger networks. They also tended to have significantly more non-conformers in their social circles.

On average, 72 percent of non-conformers' networks recommended against following the recommended vaccination schedule, versus only 13 percent of those in "conformers'" social networks. Overall, parents said that their partners were the most influential people in their networks, followed by doctors, family members and friends.

Parents who did not stick to the recommended vaccination schedule were also more likely to seek information from books, research articles and mainstream media outlets. But the variable that best predicted parents' choices was the number of people in their networks who advocated for something other than government recommendations.

"For the majority of the parents in this study, the decision came down to the percent of people in their networks saying, 'don't do this' in one form or another," study author Emily Brunson, a medical anthropologist with Texas State University-San Marcos, told The Huffington Post.

Brunson said it is unclear if the parents in the study knew whether they were going to vaccinate before having their babies, then constructed networks that reflected the decisions they made, or if the social networks influenced parents' choices.

"Are the networks driving the decisions, or are the decisions driving the networks?" she asked, adding that she hopes to tackle the question next in her research.

In the meantime, she said the study has a clear message for parents: Who they surround themselves with can have a significant impact on the decisions they make, as can what they say to family and friends.

"It, frankly, really does matter when you're having conversations with other people about vaccination," Brunson said. "It actually has a big effect."

That's something mom Ella Rucker, 40, takes very seriously. She chatted with friends and family about vaccination, and read stories about parents who were staunchly opposed to it, but Rucker ultimately decided it was important to follow the government guidelines. Though Rucker is certain it was the right decision for her 3-year-old daughter, she is careful about what she says to friends when they come to her for advice.

"I tell them what I did, and why it was right for [my daughter]," she said. "But I don't want to be responsible for what anyone else decides."

Earlier on HuffPost:

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  • Chance Of Having Twins Skyrockets

    In January, the <a href="http://www.huffingtonpost.com/2012/01/04/chances-of-having-twins_n_1183674.html">Centers for Disease Control and Prevention</a> reported that the numbers of twins in the U.S. has jumped in the last three decades: In 2009, 1 in every 30 babies born in the U.S. was a twin, compared to just 1 in every 53 in 1980. Why? Chalk it up to more and more couples using assisted reproductive technology, as well as an increase in women waiting to have kids until their 30s when the odds of having twins increases,<a href="http://www.huffingtonpost.com/2012/01/04/chances-of-having-twins_n_1183674.html"> AP said.</a>

  • U.S. Autism Rate Up

    In March, the Centers for Disease Control and Prevention released new figures on autism spectrum disorder in the U.S. and they were up: <a href="http://www.huffingtonpost.com/2012/03/30/autism-rate-increase-repo_n_1390721.html">1 in 88 children</a> is now believed to have autism, compared to the previous estimate of 1 in 110. Experts attribute much of the increase to better screening and diagnosis, AP reported, but that does not mean the findings aren't cause for concern. "Autism is now officially becoming an epidemic in the United States," Mark Roithmayr, president of Autism Speaks, said at a news conference.

  • 1 in 13 Women Drink During Pregnancy

    A <a href="http://www.huffingtonpost.com/2012/07/19/alcohol-during-pregnancy-_n_1686953.html">Centers for Disease Control and Prevention</a> survey from July found that 1 in 13 pregnant women in the U.S. drink alcohol. And of those who said they drank, 1 in 5 admitted to going on at least one binge -- having four or more drinks at once. <a href="http://www.huffingtonpost.com/2012/08/22/drinking-alcohol-pregnant-effects-children_n_1822880.html">A study</a> that came out a month later found that drinking during pregnancy has long-lasting effects on children's size.

  • Batteries Can Pose Serious Risk To Kids

    More and more kids are swallowing batteries, a Centers for Disease Control and Prevention report found, sending thousands of children to the ER each year. Between 1997 and 2010, nearly 30,000 kids up to age 4 were taken to the emergency room for battery related injuries, <a href="http://www.huffingtonpost.com/2012/08/30/swallowed-batteries-kids_n_1844412.html">MyHealthNewsDaily reported</a> in August. More than half of the cases involved small, circular button batteries.

  • AAP Throws Support Behind Circumcision

    In August, the <a href="http://www.huffingtonpost.com/2012/08/27/new-circumcision-guidelin_n_1826069.html">American Academy of Pediatrics</a> -- the U.S.' major pediatrics organization -- revised its policy on infant male circumcision, saying that the health benefits outweigh the risks. But the new guideline stopped short of recommending it routinely, stating instead that it should simply be available to parents who choose it for their sons. To the great surprise of no one, the policy was an immediate source of debate, with one "intactivist" leader <a href="http://www.huffingtonpost.com/2012/08/27/new-circumcision-guidelin_n_1826069.html">telling HuffPost</a> that the AAP had failed to address what she called the "real risks and harms of circumcision."

  • Breastfeeding Is On The Rise

    Also in August, the <a href="http://www.huffingtonpost.com/2012/08/02/breastfeeding-rates-cdc_n_1734381.html">Centers for Disease Control and Prevention</a> announced that more moms in the U.S. are breastfeeding their babies. Some 47 percent of moms breastfed their babies for at least six months in 2009 (the latest year for which there is data). That's up from 44 percent the year before. "The headlines 10 years back were, 'Mothers don't breastfeed enough; Is something wrong with mothers?'"Dr. Alison Stuebe, an OB-GYN and assistant professor of maternal and child health at the University of North Carolina <a href="http://www.huffingtonpost.com/2012/08/02/breastfeeding-rates-cdc_n_1734381.html">told HuffPost</a>. "We've recognized that this is crazy. Let's fix the system rather than going after moms.'"

  • More Kids Taking Antipsychotics

    The number of kids and teens being prescribed antipsychotics has soared, an August study in the <a href="http://www.huffingtonpost.com/2012/08/09/antipsychotics-adhd-study_n_1760602.html">Archives of General Psychiatry</a> found. Psychiatrists now prescribe the drugs in one out of every three office visits with children, and increasingly for off label use -- namely, the treatment of ADHD. The latter in particular, experts <a href="http://www.huffingtonpost.com/2012/08/09/antipsychotics-adhd-study_n_1760602.html">told HuffPost</a>, is cause for serious concern: "Although antipsychotic medications can deliver rapid improvement in children with severe conduct problems and aggressive behaviors, it is not clear whether they are helpful for the larger group of children with ADHD," study author Dr. Mark Olfson, a professor of clinical psychiatry at the College of Physicians and Surgeons of Columbia University, said.

  • Laughing Gas Safe For Delivering Moms

    Nitrous oxide, otherwise known as laughing gas, is a good way for women to manage some of the pain that accompanies labor, a <a href="http://www.huffingtonpost.com/2012/09/13/laughing-gas-delivery_n_1881496.html">Cochrane review</a> from September said. Though it's not at all popular here in the U.S. -- only 1 percent of women use laughing gas during birth, compared to the 60 percent of women who have an epidural during vaginal delivery -- the review concluded that it is both effective and safe for mom and baby.

  • Sleep Training is Safe

    Though sleep training can be a source of contention among parents and parenting experts alike, <a href="http://www.huffingtonpost.com/2012/09/10/infant-sleep-training_n_1865767.html">an Australian study</a> published in September concluded that two of the most popular methods are perfectly safe. "Controlled comforting" (basically a modified form of cry-it-out) and "camping out" (when parents sit in the room with their babies and pat or comfort them, but do not feed or cuddle them to sleep), did not have any impact -- good or bad -- on children when researchers looked at them at age 6.

  • Birth Complications Up In the U.S.

    They're still rare, but severe complications from birth are on the rise in the U.S., <a href="http://www.huffingtonpost.com/2012/10/24/us-birth-complications_n_2008771.html">Reuters reported</a> back in October. A Centers for Disease Control and Prevention study found that between 1998 and 2009, the rate of major complications, including things like severe bleeding and kidney failure, essentially doubled. Though <a href="http://www.huffingtonpost.com/2012/10/24/us-birth-complications_n_2008771.html">experts stressed</a> that most women who give birth are perfectly fine, there has been an increase in women giving birth at older ages, as well as women who are obese or have certain health conditions that up their risk, such as high blood pressure.

  • Boys Entering Puberty Earlier And Earlier

    Research published in October in the journal <a href="http://www.huffingtonpost.com/2012/10/20/boys-puberty_n_1987979.html">Pediatrics</a> showed that boys in the U.S. are entering into puberty at ever earlier ages: On average, boys are starting puberty six months to two years sooner than previous data showed. The study, which is among the first to look at the issue of early-onset puberty in boys, found that white and Hispanic boys now start to show signs of puberty when they are 10, while African American boys may start to show signs when they are 9 years old. What exactly this means isn't yet clear, <a href="http://www.huffingtonpost.com/2012/10/20/boys-puberty_n_1987979.html">study researchers said</a>, but it flags an issue that warrants further investigation.

  • Kids See 'Startling' Amounts Of Background TV

    A lot of parents limit the amount of TV their kids watch each day, but <a href="http://www.huffingtonpost.com/2012/10/01/children-tv-exposure-study_n_1923719.html">research published in October</a> found that many are nonetheless exposed to a lot of it -- in the background. The study, which ran in the journal <a href="http://www.huffingtonpost.com/2012/10/01/children-tv-exposure-study_n_1923719.html">Pediatrics,</a> found that kids are generally exposed to at least 4 hours of background TV per day (meaning it's on in the same room they're in, even if they're not watching directly) and children under the age of 2 are exposed to 5.5 hours every day.

  • Antidepressants May Carry Risks For Pregnant Women

    A November study in the journal <a href="http://www.huffingtonpost.com/2012/11/08/antidepressants-pregnancy_n_2094155.html">Human Reproduction</a> caused quite a stir when it suggested that SSRIs, a type of antidepressants, may increase the risk of complications when taken during pregnancy. Problems include risk of miscarriage, birth defects, neurobehavioral problems and more, the study researchers said. But there was significant push back from many mental health experts who rushed to write letters to the editor saying that the study ignored the many risks of untreated depression.

  • Preterm Births Hit 10-Year Low

    In November, the <a href="http://www.huffingtonpost.com/2012/11/13/us-preterm-birth-rate-hit_n_2118244.html">March of Dimes</a> released its annual preemie birth rate report card and, overall, the news was good: The U.S. preterm birth rate was the lowest it has been in a decade, dropping to 11.7 percent. While that is certainly welcome news, the U.S. still has a long way to go, March of Dimes experts <a href="http://www.huffingtonpost.com/2012/11/13/us-preterm-birth-rate-hit_n_2118244.html">told HuffPost.</a> Overall, the country still only earned a "C" and only four states (Vermont, Oregon, New Hampshire and Maine) earned an "A."