Many have seen someone throw a cold stare in the direction of a pregnant woman ordering a second glass of wine or, heaven forbid, smoking a cigarette.
But with the list of potentially dangerous foods growing by the day, an expectant mother shouldn't be surprised if a stranger pipes up as she buys a box of macaroni and cheese.
"Your doctor said you could eat that?" Tut-tut.
Every month that passes brings new studies saying this food is good for you and that food is bad. Pregnant women experience this information overload in exponential terms. And many around them feel they have the right to weigh in when lunchtime arrives.
Research over the past few years has added common foods and beverages to the list of items that pregnant women should avoid. Studies have linked maternal consumption of both diet and regular soda with preterm delivery and preeclampsia in mothers, higher body mass indexes in infants, and overweight and asthmatic children.
Other studies have found that a foetus may be exposed to arsenic when the mother eats rice, potentially affecting foetal growth. And in July, a widely publicised report found high levels of phthalates, chemicals that in large amounts can impede testosterone production in male foetuses, in macaroni and cheese mixes.
Although none of these foods currently appear on the American Pregnancy Association's Foods to Avoid list, Brad Imler, the organisation's president, advises women to exclude them anyway.
It's the better-safe-than-sorry school, though some would call it pregnancy paranoia. Unless a woman is constantly monitoring the latest in scientific journals, staying informed of potential dangers is almost impossible.
Even then, only experts can tell you which studies and headlines are valid and which are hyperbolic.
"It's really hard to keep up," says Elisabetta Politi, a dietitian at Duke Health.
"We're bombarded with so many studies, and many are observational, so we don't know if the food is causing an increased risk or [just] associated with it. But it's the time in life where women are willing to make changes and err on the safe side."
Such thinking, though, can lead to unnecessary dietary changes, not to mention anxiety, warns economist Emily Oster. In her 2013 book, Expecting Better: Why the Conventional Pregnancy Wisdom Is Wrong - And What You Really Need to Know, Oster provides a guide on how to get through a pregnancy healthfully, safely, and without missing out unnecessarily.
For example, don't worry about causing foetal alcohol syndrome from a little bit of wine, but do worry about listeria exposure through unwashed vegetables and deli turkey. Oh, and don't smoke. Ever.
Soda studies vary in samples and methodologies, but each uses large cohorts of mother-child pairs to assess the potential impact of naturally sweetened and artificially sweetened beverages consumed during pregnancy.
The APA's Imler says soda should be avoided, full stop. Oster isn't overly concerned. Research that seems to measure soda intake, she says, might actually be measuring a healthy diet, because women who drink soda may be less concerned with eating right, for example.
Indeed, the risk of mixing up factors is listed in soda studies as a potential limitation, though the researchers note their efforts to narrow down the causes. "The risk of confounding is always great," says Thorhallur Halldorsson, a senior research scientist at the Centre for Fetal Programming at the Statens Serum Institute in Copenhagen.
Halldorsson was the lead author of a 2010 study of almost 60,000 Danish women that found an association between consumption of artificially sweetened soft drinks and preterm delivery.
Ultimately, says Emily Oken, a professor at Harvard Medical School and researcher on the soda-related asthma and childhood adiposity studies, there's no reason pregnant women would be harmed by consuming less soda. There are plenty of other reasons not to drink it.
"I never want people to panic," Oken says. "The occasional beverage is not going to create some lasting harm." Nevertheless, she says, water, milk, or tea are always a better way to go.
Oster agrees, saying there's a big difference between a soda now and then and several a day.
"The biggest takeaway is it's not a good idea to drink five Cokes a day," she says. "That's not something we would recommend to people, pregnant status or not."
The American Beverage Association, the lobbying organization that supports soda manufacturers, rejects the scientific community's oft-stated conclusion that soda consumption can have negative health effects. In fact, it contends that its products are safe for pregnant women.
"The European Food Safety Authorityhas affirmed that low- and no-calorie sweeteners in beverages and foods can be safely consumed during pregnancy," says Lauren Kane, an ABA spokeswoman, in a statement.
The EFSA did state in 2013 that it generally found no health risks associated with moderate consumption of the sweetener aspartame, but two 2010 studies (including Halldorsson's) mentioned in a 2011 EFSA abstract concluded the sweetener may indeed have deleterious effects.
The EFSA concluded, however, that the studies weren't sufficient to warrant changing its position on aspartame.
Conflicting studies notwithstanding, pregnant women can easily avoid sodas. But the presence of arsenic in rice presents a different challenge, in part because the grain is usually considered a health food.
The presence of arsenic is something to take seriously, because there's plenty of evidence showing that pollutants can harm foetuses, Oster says. How does poison end up in rice? Soil and water used to grow rice soak it up from nearby industry or waste.
"That's something we should be concerned about," says Wahida Karmally, director of nutrition at Columbia University College of Physicians and Surgeons. She puts arsenic in the same category as mercury, which is found at high levels in certain fish species, such as mackerel, shark, and tilefish.
"We would advise expecting mothers to avoid anything that is connected to arsenic," the APA's Imler says.
Some chemicals "may not be harmful to an adult -however, developing babies are much more susceptible." USA Rice, a lobbying group for the industry, didn't respond to a request for comment.
As with soda, not everyone takes such an absolutist stance.
"Just don't go crazy on rice," says Politi, of Duke Health. Indeed, in countries such as Japan and China, much of the population consumes rice more than once a day, says Zhaoping Li, center director and division chief, clinical nutrition of UCLA Medical Center.
"But we have not seen an increase of birth defects or other issues," she says.
As for boxed macaroni and cheese and other highly processed foods that could have phthalates, it's probably OK to have some every once in a while, but you can be certain no harm will come to you from skipping it.
The Grocery Manufacturers Association says the safety of phthalates found in boxed mac and cheese has been reviewed by the Food and Drug Administration, which confirmed "dietary exposure remains well below the permitted safety limits."
So, for those entering the third trimester who are now worried about all the bad things they ate in the past six months, take it easy.
"Don't panic if you accidentally drink a sugary beverage," Oken says. "We know anxiety is bad for pregnancy, too."