Smoking, poor nutrition and even working late have been cited among the top reasons why babies might be born with low birth weight, but a team of researchers from Yale say healthcare isn't the only cause.

According to a study published in the Annals of Behavioral Medicine, Valerie Earnshaw and her colleagues at Yale found that racism against the more than 1,000 black and Latina girls they surveyed resulted in lower birth weight babies as well.

The contributing factor, they say, was the depression that resulted from the mothers-to-be's experience with discrimination, including being treated with less respect than other people, receiving poorer service or being called names.

Earnshaw and her colleagues interviewed 420, 14- to 21-year-old black and Latina women at 14 community health centers and hospitals in New York, during the second and third trimesters of their pregnancies, and at six and 12 months after their babies had been born, according to a news release. The team also measured the women's reported experiences of discrimination, depressive symptoms, pregnancy distress and pregnancy symptoms.

Their finding is one that researchers have acknowledged for years.

In 2010, researchers at the University of Washington, The Ohio State University, and the University of Pittsburgh concluded that pregnant women are at greater risk of delivering prematurely or giving birth to infants with low birth weight if they are diagnosed with clinical depression.

And while the women in Earnshaw's study reported relatively low levels of discrimination, the impact of discrimination was the same across the board.

According to the CDC, a birth weight of less than 5.5 pounds is considered low and can result in increased risk of infection, delayed motor skills and learning disabilities.

Earlier on HuffPost:

5 Barriers To Pregnancy Success (Besides Your Biological Clock)
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  • Uterine Fibroids

    "Black women have about a three times greater incidence of fibroids compared to white women," Dr. Ashton says. Black women also appear to have larger and more numerous fibroids, which are described as benign tumors made up of smooth muscle and the proteins collagen and elastin, <a href="" target="_hplink">according to the Agency for Healthcare Quality and Research</a>. Where fibroids are located on the uterus is what determines their affect on fertility, Ashton explains. "Usually, if they're sitting on top, the outside of the uterus, they don't cause that much of a problem for infertility, but if they are in the muscle wall or if they're pushing into the cavity of the uterus, those are the types that can significantly affect fertility," she says. While many fibroids are asymptomatic, those pushing into the cavity often cause symptoms including heavy menstrual bleeding or prolonged periods, lasting more than a week. Larger fibroids can also cause pelvic pain or pressure, along with frequent urination, difficulty emptying your bladder, constipation and back aches. Treatment options including hysterectomies and uterine fibroid embolization have historically not considered women who still want to have kids, but newer, laparoscopic techniques that allow doctors to surgically burn or <a href="" target="_hplink">freeze off the fibroids</a> are safe for women who want to conceive, Dr. Ashton says.

  • Excess Weight

    Studies have found that obese women have a harder time becoming pregnant than thinner women -- possibly because of how excess fat affects hormone levels and inflammation throughout the body. "We do know that African-American women tend to have <a href="" target="_hplink">higher rates of obesity</a> and that causes hormonal disruptions that can affect their ability to become pregnant," Dr. Ashton says. "Essentially, obesity is an inflammatory condition." In a report release last year, both <a href="" target="_hplink">minority women and those who were overweight had lower rates of success with infertility treatment</a>, with only 36 percent of African Americans becoming pregnant following the treatment, compared to 45 percent of whites. Of the women who became pregnant and didn't miscarry in the first 22 weeks, birth rates were lower among minorities.

  • STIs

    Sexually transmitted infections are another risk factor for infertility, Dr. Ashton says, particularly chlamydia, which very often does not have the same pelvic inflammatory symptoms -- pain and fever -- as other STIs. "It's a more indolent type of infection and it can cause a lot of damage before a woman knows she has it," she says. Complications of gonorrhea can also do serious damage to your fertility by causing scaring in the fallopian tubes and making it difficult for an egg to pass through. <a href="" target="_hplink">According to the CDC</a>, the rate of gonorrhea among blacks was 18.7 times the rate among whites in 2010 -- the highest among all racial and ethnic groups. The same has proven true for <a href="" target="_hplink">chlamydia, which is eight times higher among blacks than whites</a>. "We see this from a very early age," Dr. Ashton says, citing a study that showed six percent of some 27,000 high school students tested positive for an STI. In addition, those who tested positive were more likely to be female and more likely to be black. "If you're getting these infections early in life, it probably does not bode well for fertility later on," she says.

  • Endometriosis

    Though an estimated <a href="" target="_hplink">2 to 10 percent of women of reproductive age have endometriosis</a>, a condition that occurs when tissues that usually line the uterus become implanted on the outside instead, women of African descent are thought to be rarely, if ever, affected. A study presented last year at Howard University Hospital, however, found that <a href="" target="_hplink">African-American women with endometriosis are often misdiagnosed</a>, and that more of these women are suffering from the condition than the old statistics have shown. "[Endometriosis] can cause significant adhesions and tubal damage," Dr. Ashton says, referring to damage to the fallopian tubes. But not all women, especially those with mild endometriosis, will have infertility, according to experts at the <a href="" target="_hplink">National Institutes of Health</a>. Laparoscopy to remove scarring related to the condition may help improve your chances of becoming pregnant.

  • Male Infertility

    "Before a woman even undergoes an infertility workup, you need to make sure that you've ruled out male infertility," Dr. Ashton says, pointing to stats showing that in one-third of cases, infertility is due to a cause involving only the male partner. "In general, they say about 30 percent is male contribution, 30 percent female and 30 percent of the time you may not be able to find a recognizable reason why," she says. According to the Mayo Clinic, the most common <a href="" target="_hplink">causes of male infertility include</a>: <strong>Abnormal sperm production or function</strong> due to various problems, such as undescended testicles, genetic defects or repeated infections. <strong>Problems with the delivery of sperm</strong> due to sexual problems, such as premature ejaculation or painful intercourse (dyspareunia); health issues, such as retrograde ejaculation; certain genetic diseases, such as cystic fibrosis; or structural problems, such as blockage of the part of the testicle that contains sperm (epididymis). <strong>General health and lifestyle issues</strong>, such as poor nutrition, obesity, or use of alcohol, tobacco and drugs. <strong>Overexposure to certain environmental factors</strong>, such as pesticides and other chemicals. In addition, frequent exposure to heat, such as in saunas or hot tubs, can elevate your core body temperature. This may impair your sperm production and lower your sperm count. <strong>Damage related to cancer and its treatment</strong>. Both radiation and chemotherapy treatment for cancer can impair sperm production, sometimes severely. The closer radiation treatment is to the testicles, the higher the risk of infertility. Removal of one or both testicles due to cancer also may affect male fertility. <strong>Age</strong>. Men older than age 40 may be less fertile than younger men.

  • Age

    Contrary to what you may have heard, there is no magic number when it comes to your fertility. "There is a range," Dr. Ashton says. And according to the March of Dimes, <a href="" target="_hplink">1 in 5 women in the United States has her first child after age 35</a> nowadays. Though a <a href="" target="_hplink">new test called AMH</a> can reportedly erase all doubt, pinpointing exactly how many eggs a woman has left at any point in time, a recent report by CNN revealed that <a href="" target="_hplink">a woman's eggs may not age in tandem with her body</a> (meaning that a woman in her thirties may have the eggs and fertility chances of a woman much older). Along with the number of eggs you have, quality also diminishes with age, and certain lifestyle factors -- including smoking, alcohol and caffeine consumption (think 6 cups a day) and excess weight gain -- only speed up the process, Dr. Ashton says. Age also increases your risk of developing chronic medical conditions, such as high blood pressure and cardiovascular disease, outcomes that she says can directly affect your fertility. According to the <a href="" target="_hplink">American Diabetes Association</a>, women with type-2 diabetes have an increased risk of developing polycystic ovarian syndrome (PCOS), a hormonal imbalance that can cause cysts on the ovaries and prevent eggs from being released in a normal menstrual cycle. PCOS is said to be the leading cause of infertility among women.