Experts are still trying to piece together what factors contribute to the development of autism. Recent research suggests that changes that occur during conception, pregnancy, and possibly even delivery may increase the risk of autism in children who are genetically predisposed to the disorder.
One study in the New England Journal of Medicine found differences in the brains of children with autism as early as the second trimester of pregnancy. While researchers haven't been able to pinpoint a definite cause, ASD likely develops from a combination of factors. "Some cases may primarily have a genetic cause, and others may have a primarily environmental cause, but most cases probably result from the interaction of both," says Paul Wang, M.D., senior vice president of medical research for Autism Speaks.
While you can't do much to change genetics, you can alter your exposure to certain environmental factors that have shown a link to ASD. However, none of these lifestyle changes are absolutes—experts can't tell you that lowering your exposure to one particular factor will lower your child's risk.
"Evidence about environmental risk during pregnancy is really at its infancy, so any data-supported hypotheses must be investigated further as nothing is yet considered a certain cause," says M. Daniele Fallin, Ph.D., director of the Wendy Klag Center for Autism and Developmental Disabilities at the Johns Hopkins Bloomberg School of Public Health. The key is for pregnant women to take some safe, proactive steps like these that can potentially protect their babies.
A 2014 study in the American Journal of Epidemiology found that children born to iron-deficient mothers are five times more likely to develop autism. The risk increases when the mother is age 35 or older or has a metabolic condition such as obesity, high blood pressure or diabetes. Iron is crucial to fetal brain development, yet up to half of all pregnant women don't get enough of it.
Researchers looked at the iron intake of close to 900 women during three critical stages: three months prior to becoming pregnant, throughout pregnancy and after delivery while breastfeeding. The mothers of children with autism were significantly less likely to take iron supplements before, during and/or after their pregnancies than the mothers whose children were developing typically.
This study is the first to examine the relationship between maternal iron intake and autism risk. To confirm a connection and the study's validity, more researchers need to replicate the findings in larger research groups.
"While there's no clear indication that iron deficiency during pregnancy causes autism, we know that iron is critical to the in utero development of a baby's nervous system," says Raphael Bernier, Ph.D., clinical director of the Autism Center at Seattle Children's Hospital.
That's why it's important to get enough iron in your diet via foods, such as meats, seafood, eggs and iron-fortified breads and cereal, and to take an iron-fortified prenatal supplement when you're trying to conceive and when you're expecting.
"Perhaps the most convincing and consistent environmental association with autism risk to date is pregnancy exposure to air pollution," says Dr. Fallin. Multiple studies have shown this connection: One by researchers at the Harvard School of Public Health found that the risk doubled for children born to women exposed to high levels of pollution, particularly in the third trimester. The higher the levels of exposure, the greater the risk.
However, that's just part of the story.
"The challenge has become understanding what component of air pollution may be relevant, as this implicates hundreds of chemicals from multiple sources," explains Dr. Fallin. In general, the American Lung Association recommends several ways to protect yourself from air pollution: for instance, fill your gas tank up after dark, exercise away from highly-trafficked areas and, when pollution levels are high, take your workout indoors. You can check out your daily air quality levels at www.airnow.gov.
A 2014 French study conducted on mice and published in the journal Science suggests that the use of spinal anesthesia during labor results in higher concentrations of chloride or salt in the brains of newborn mice. The authors hypothesize that this may increase the risk of autism in humans.
High chloride levels are essential to a baby's brain development while in utero. During labor and delivery, a baby is exposed to oxytocin, the hormone that brings on contractions. Oxytocin acts as a diuretic and naturally lowers an infant's chloride levels. Researchers believe epidurals may interfere with the release of oxytocin causing chloride levels to remain high after birth.
The study seems to support earlier findings from a 2012 clinical trial of 60 children with autism who saw some improvements in their behaviors after taking a diuretic that lowered their chloride levels. However, the Science study on epidurals and chloride was conducted solely on mice. While animal studies are important, the findings don't always translate to people.
"For one thing, animals don't have symptoms of autism in the same way that people do," says Susan Hyman, M.D., division chief of neurodevelopmental and behavioral pediatrics at the University of Rochester Medical Center in New York and chair of the American Academy of Pediatrics' (AAP) Council of Children with Disabilities Autism Subcommittee.
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What's more, the study didn't address what happens when a mother's labor is induced with pitocin, a synthetic version of oxytocin. "As a mother, I know that epidurals made my deliveries more comfortable," says Dr. Hyman. "I don't think it's prudent to deviate from a helpful obstetrical practice based on one animal study."
Research from the University of Utah published in the November 2013 issue of Pediatrics suggests a potential link between excess pregnancy pounds and autism risk. The American Congress of Obstetricians and Gynecologists (ACOG) recommends women gain no more than 35 pounds during pregnancy (it's 25 pounds if you're already overweight). In the study, incremental 5-pound increases in weight above ACOG's recommendation were linked to a slightly higher, yet significant risk for autism.
Previous studies indicate a possible connection to a woman's pre-pregnancy body mass index (BMI), pregnancy weight gain, and a child's risk of autism. One theory is that excess body fat may change a woman's hormone levels or cause inflammation that affects fetal brain development. "Obesity rates and autism rates have both gone up over the past decades, yet that doesn't mean the two are connected," says Anna Maria Wilms Floet, M.D., a behavioral developmental pediatrician at the Kennedy Krieger Institute's Center for Autism and Related Disorders in Baltimore. The bottom line: "Women should watch their weight gain during pregnancy to prevent problems like diabetes and high blood pressure," says Dr. Wilms Floet.
There seems to be an increased risk for ASD associated with maternal exposure to certain chemicals during pregnancy, thought a lot more research needs to be done. For instance, one recent study found environmental exposures associated with autism, specifically "traffic-related pollutants, some metals, and several pesticides and phthalates." It can get confusing to figure out exactly which chemicals, such as those found in flame-retardants, plastics, and even cosmetics, to avoid. Talk to your doctor about what's right for you—you might want to limit your intake of canned foods, avoid water bottles made of plastic or aluminum, and stay away from personal care products that list "fragrance" as an ingredient.
An April 2015 study in the Journal of the American Medical Association (JAMA) found that mothers-to-be who are diagnosed with gestational diabetes by their 26th week of pregnancy are 63 percent more likely to have a child with autism. That means for every 1,000 women with gestational diabetes, seven of them may have a child with autism. Researchers speculate that in utero exposure to high blood sugar may affect a baby's brain development and heighten the risk for developmental disorders.
Earlier studies also have shown a possible connection between high blood sugar during pregnancy and autism risk. The key factor may be how high blood sugar levels get. Interestingly, the JAMA study found that babies born to mothers who had type 2 diabetes before getting pregnant didn't have a higher risk of autism, perhaps because the women were taking medication to control their blood sugar levels.
Gestational diabetes poses a number of problems for infants, including preterm labor, large birth-weight and an increased risk of obesity and type 2 diabetes later in life. Moms-to-be have a higher risk of developing high blood pressure, preeclampsia and type 2 diabetes, as well. "All expectant women should strive to keep their blood sugar under control, regardless of these study findings," says Dr. Wilms Floet.
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Researchers have found potential links between the medication a mother takes while pregnant and autism risk. For instance, use of anti-depressants (SSRIs specifically) has shown association with autism across multiple studies, says Dr. Fallin, though it remains unclear whether this link is related specifically to the drugs or to the mother's depression itself. Also, a study in the Journal of the American Medical Association has shown that valproate, a medication used to treat epilepsy and other neurological disorders, can increase the risk for autism. It's crucial that you work with your doctor to determine whether the benefits of any medications you take outweigh the risks. In many cases, they will: "If a mother has epilepsy, it is very important that it be controlled during pregnancy, even if that requires valproate," explains Dr. Wang. "If the mother has a seizure while pregnant, that is potentially a much bigger risk to the fetus than the drug that controls her seizures."
A study in the Journal of the American Academy of Child & Adolescent Psychiatry found that pregnancies spaced between 2 and 5 years apart have the lowest risk of a child developing autism. Researchers found that those children conceived after less than 12 months were 50 percent more likely to end up with a diagnosis as compared with children conceived between that 2-and-5-year time frame, though it's unclear why.
Meanwhile, those conceived after more than 60 months were 30 percent more likely to be diagnosed. However, keep in mind that autism risk increases with both parents' ages at conception and that a woman's fertility declines as she gets older. When it comes to timing, work with your doctor to determine the best plan for you and your family.
A 2011 Epidemiology study found that taking prenatal vitamins three months before conception and during at least the first month of pregnancy halves a child's autism risk. Women with a strong genetic link to the disorder who didn't take vitamins were up to seven times more likely to have a child with autism. Additional studies suggest high levels of folic acid, a B vitamin important for brain development, are key.
All women of childbearing age (even those who aren't trying to conceive) should get between 400 to 800 micrograms (mcg) of folic acid every day. Most women get about 150 mcg of daily folic acid from fortified foods such as breads and cereal.
A 2012 American Journal of Clinical Nutrition study suggests that women need at least four times that amount -- 600 mcg -- to lower autism risk. Check your vitamin's nutrient label, and if necessary, discuss upping your folic acid intake with your doctor, and add more foods rich in folate (like lentils, spinach, and broccoli) to your diet.
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Researchers know that maternal health during pregnancy has an impact on the unborn child, and ASD is certainly no exception to this rule. "For instance, women who are severely ill and require hospitalization during pregnancy may be more likely to have children who develop autism," says Dr. Wang. Specifically, studies have shown associations between maternal infections during pregnancy and subsequent risk for their children developing an autism spectrum disorder.
In general, women should do what they can to remain healthy during pregnancy. "This includes optimizing nutrition, taking prenatal vitamins as recommended by their obstetrician, avoiding exposure to unnecessary drugs and medications, and ensuring that their own vaccinations are up to date," says Dr. Wang. Also, a recent study in the Journal of the American Medical Association found that gestational diabetes developed by 26 weeks is linked with an increased risk to ASD. Ask your doctor about the right plan for you and then stick with it.