One study looked at depressed fathers of one-year olds, and the other examined pregnant mothers under stress.

The children of women who experience a stressful life event either during or before pregnancy are at an increased risk of being hospitalized from infectious disease, according to a new study.

Children whose mothers experienced a stressful event, such as the death of a loved one or divorce, while they were pregnant were 71 percent more likely to be hospitalized with a severe infectious disease than children of women who did not undergo prenatal stress, said study researcher Nete Munk Nielsen, an epidemiologist at Statens Serum Institute in Denmark.

And the children of women who experienced a stressful life event 11 months before conception were 42 percent more likely to be hospitalized with severe infectious disease than the children of stress-free women, Nielsen said.

"We speculate that this is due to effects of longer-lasting stress following the stressful life event."

The study was published online last week in the American Journal of Epidemiology.

Researchers looked at the health data for 1,670,269 Danish children born between 1977 and 2004, and asked their mothers if they experienced the death of a spouse or a child,

or had gotten a divorce before or during pregnancy. The children were followed from four weeks after birth until they turned 15.

Researchers chose to measure stress by these events because "death of a spouse, death of a child and divorce are considered some of the most devastating and stressful life events," Nielsen said.

Researchers found a 71 percent increased risk of hospitalization from infectious disease for children who were exposed to their mother's stress while still in the womb.

Children whose mothers experienced a stressful event 11 months before conception had a 42 percent increased risk of  hospitalization from infectious disease, but there was no association between a child's infectious disease risk and a mother's stress 12 to 35 months before conception (up to three years before conception), the study said.

And kids exposed to prenatal stress were 67 percent more likely to be hospitalized during their first year of life than children whose mothers didn't undergo a major stressful event, according to the study.

The reasons why a mother's stress can carry over to her child's immune function aren't exactly known, but it's possible that a woman who experiences a stressful event while pregnant may also adopt unhealthy behaviors like smoking, drinking alcohol, eating poorly or using medications that could affect her child's immune system, Nielsen said.

Biologically, it's may be possible that maternal stress hormones, high amounts of which are produced during pregnancy, are transferred from mother to fetus. These stress hormones could be acting on a part of the fetal brain that regulates the immune system, said Kathleen M. Gustafson, director of fetal biomagnetometry at the University of Kansas Medical Center, who was not involved with the study.

Poor immune function is not the only aspect of health that can be affected by maternal stress, Gustafson said. Preterm birth, being born small for gestational age, spontaneous abortions, developmental delays and increased risk of schizophrenia are all possible effects, she said.

"Normal pregnancy, in and of itself, is a maternal metabolic stress test," Gustafson said.

Past research has also shown that mothers who are stressed out during pregnancy have kids with heightened immune systems and an increased sensitivity to allergens.Harvard Medical School researchers presented work in 2008 to the American Thoracic Society that showed that the higher the level of prenatal stress mothers were exposed to, the higher the expression of immunoglobulin E in their babies' cord blood. Immunoglobulin E is a marker of a person's immune system; the more there is, the higher the risk of asthma and allergy.

However, it's important to note that the stressful events in the new study are different from the normal kinds of stress people encounter every day, Gustafson said.

"This publication deals with significant, life-altering events; not the kind of daily events we call 'stress' like getting stuck in traffic or missing your flight at the airport," Gustafson said. "We need to 'stress' that, if you will otherwise we're causing undue stress to women who are doing their best to maintain a healthy pregnancy."

The other study looked at new fathers. Just like new moms, new fathers can be depressed, and a study found a surprising number of sad dads spanked their 1-year-olds.

About 40 percent of depressed fathers in a survey said they'd spanked kids that age, versus just 13 percent of fathers who weren't depressed. Most dads also had had recent contact with their child's doctor;  a missed opportunity to get help, authors of the study said.

The American Academy of Pediatrics and many child development experts warn against spanking children of any age. Other studies have shown that kids who are spanked are at risk of being physically abused and becoming aggressive themselves.

The researchers said spanking is especially troubling in children who are only 1, because they could get injured and they "are unlikely to understand the connection between their behavior and subsequent punishment."

The study was released online in the journal Pediatrics.

The authors analyzed data on 1,746 fathers from a nationally representative survey in 16 large U.S. cities, conducted in 1999-2000. Lead author Dr. Neal Davis said that was the most recent comprehensive data on the subject, and he believes it is relevant today. Depression among fathers is strongly tied to unemployment rates, which are much higher now than a decade ago, he said.

The men were questioned about depression symptoms, spanking and interactions with their 1-year-olds, but weren't asked why they spanked or whether it resulted in physical harm. Overall, 7 percent of dads had experienced recent major depression. Some likely had a history of depression, but in others it was probably tied to their children's birth, similar to postpartum depression in women, Davis said. A pediatrician now with Intermountain Healthcare in Murray, Utah, Davis did the research while at the University of Michigan.

Postpartum depression is more common in women; by some estimates as many as 25 percent develop it shortly after childbirth. Severe cases have been linked with suicide and with deaths in children including several high profile drownings. Less is known about depression in new dads and the study raises important awareness about an under-recognized problem, said Dr. Craig Garfield, an assistant pediatrics professor at Northwestern University and co-author of a Pediatrics editorial.

With fathers increasingly spending time on child-care, including taking their kids to routine doctor visits, it's important for pediatricians to pay attention to dads' mental health, Garfield said. Close to 80 percent of depressed and non-depressed dads had recent contact with their child's doctor, according to the study. Davis said his office is working on screening dads for depression and offering referrals to mental health services, a practice he and his co-authors recommend for all pediatricians.

Besides being more likely to spank, depressed dads were less likely to read to their kids,  an activity the researchers called part of positive parenting. About equal numbers of depressed and non-depressed dads reported other positive interactions, such as playing games with their kids. The researchers said reading requires more focus that may be difficult when depressed.