Although life offers no guarantees, parents-to-be can increase their chances of having a healthy baby by, among other things, undergoing prenatal testing and making sure mom has a healthy pregnancy.

But almost 2,500 years after Euripides noticed that "the gods visit the sins of the fathers upon the children," scientists are discovering that nature can be even crueler than the ancient Greek imagined: It can visit the sins of the grandparents on the children.

Such "transgenerational" effects are the latest focus of a growing field called fetal programming, or the fetal origins of adult diseases. It examines how conditions in the womb shape physiology in a way that makes people more vulnerable decades later to cardiovascular disease, diabetes, immune problems and other illnesses usually blamed on genetics or lifestyle, not on what arrived via the placenta. If a fetus is poorly nourished, for instance, it can develop a "thrifty phenotype" that makes it really good at getting the most out of every meal. After birth, that lets it thrive if food is scarce, but it's a recipe for Type 2 diabetes in a world of doughnuts and fries. Poor fetal nutrition can lead to hypertension, too: If it causes the fetus to produce too few kidney cells, the adult that the fetus will become won't be able to regulate blood pressure well.

Now, in a finding that seems to put our fate even further outside our control, researchers are seeing generation-skipping effects.

Last month, scientists reported that a child whose grandmother smoked while pregnant with the child's mother may have twice the risk of developing asthma as a child whose grandma didn't flood her fetus with carcinogens. Remarkably, the risk from grandma's smoking was as great as or greater than from mom's. Kids whose mothers smoked while pregnant were 1.5 times as likely to develop childhood asthma as children of nonsmoking moms. Kids whose grandmothers smoked while pregnant with mom were 2.1 times as likely to develop asthma, scientists reported in the journal Chest.

The harmful effects of tobacco, it seems, can reach down two generations even when the intervening generation -- mom -- has no reason to suspect her child may be at risk.

"Even if the mother didn't smoke, there was an effect on the grandchild," says Frank Gilliland of the University of Southern California, Los Angeles, who led the study of 908 children. "If smoking has this transgenerational effect, it's a lot worse than we realized."

What causes the grandma effect? One suspect is DNA in the fetus's eggs (all the eggs a girl will ever have are made before birth). Chemicals in smoke might change the on-off pattern of genes in eggs, including genes of the immune system, affecting children who develop from those eggs. Men whose mothers smoked don't seem to pass on such abnormalities, probably because sperm are made after birth.

Animal data hint at other grandma effects. Last week, scientists reported the first discovery that obesity and insulin resistance, as in Type 2 diabetes, can be visited on the grandkids of female rats that ate a protein-poor diet during pregnancy, lactation or both. Again, this occurred even when those rats' offspring, the mothers of the affected grandkids, were healthy, Elena Zambrano of the Institute of Medical Sciences and Nutrition, Mexico City, and colleagues report in the Journal of Physiology.

The findings, says Peter Nathanielsz of the University of Texas Health Sciences Center, San Antonio, "stretch the unwanted consequences of poor nutrition across generations."

In people, the type of "nutritional insult" to the fetus doesn't seem to matter. Too few calories, too little protein, too few other nutrients can all lead to diabetes, hypertension and other ills decades later. "That suggests that what links diet to adult diseases is something quite fundamental," says Simon Langley-Evans of the University of Nottingham, England. The key suspects: changes in DNA activity in the fetus or in the balance of hormones reaching it via the placenta.

Alarmingly, the list of what can be passed along to the next generation is growing. If you are undernourished as a first-trimester fetus, you won't pad your hips and thighs with enough fat tissue. If, as a child or adult, you take in more calories than you expend, the extras get stored in and around abdominal organs rather than on the thighs and hips, says Aryeh Stein of Emory University, Atlanta. One result is a body shaped like an apple (which brings a higher risk of heart disease). Another is a higher risk of gestational diabetes, in which blood glucose levels rise during pregnancy and too much glucose reaches the fetus. Babies born to moms with gestational diabetes have a higher risk of Type 2 diabetes.

When undernourished fetuses grow into adolescents, they don't respond as well to vaccines as babies who had a healthy gestation, scientists led by Thomas McCune of Northwestern University, Evanston, Ill., find. One reason may be that the third trimester is a critical time for development of the thymus, which produces the immune system's T cells. When immune-compromised girls become pregnant, they have less chance of having a healthy pregnancy and a healthy baby. Score another for the grandma effect.