Is caffeine really off-limits during pregnancy? Experts weigh in on a contested topic

From raw fish to unpasteurized cheeses to lying on the right side, pregnancy comes with an extensive list of health guidelines.

Often included with the “do-nots” are alcohol, tobacco and caffeine, although the latter comes with conflicting and ever-changing data.

In 1973, two Seattle physicians coined the term “fetal alcohol syndrome.” They essentially grouped a host of birth defects and found a common denominator among the sick newborns: beyond moderate alcohol consumption on the part of the mother, according to the National Institutes of Health.

Decades later, studies increasingly demonstrated a correlation between tobacco use and negative side effects for the fetus.

Today, though, guidelines regarding caffeine during those prenatal months are far from clear. Instead, it’s difficult to decipher the “official” recommendation, partially because many medical resources have differing messages.

Dr. Lacey Marks is a board-certified obstetrician and gynecologist for the MultiCare Rockwood Group. When she needs to provide her pregnant patients with up-to-date guidelines on caffeine, she refers to the American College of Obstetricians and Gynaecologists.

That organization claims “moderate caffeine consumption (less than 200 mg per day) does not appear to be a contributing factor in miscarriage or preterm birth.”

In keeping with the organization’s guidelines, Marks relies on the 200 mg figure when patients inquire about caffeine. That is about one 12-ounce cup of brewed coffee. It’s important to note that caffeine is present in high quantities in tea (including green), energy beverages, soft drinks and even chocolate (in its many forms).

Spokane OBGYN relies on the same figure in its caffeine recommendation: “High caffeine intake has been associated with an increased risk of miscarriage. Limit your daily caffeine intake to 200 milligrams or less.”

When it comes to how caffeine would impact a fetus, Marks cited three primary concerns, including one expressed by Spokane OBGYN: increased risk of miscarriage, increased chance of preterm delivery and an impact on the baby’s size and growth.

These potential effects are made possible because of caffeine’s inherent ability to venture through blood vessels. If in the pregnant person’s system, “caffeine does cross the placenta at all times.”

Blood pressure also typically elevates as a result of caffeine, which could further impact the fetus.

Potentially more concerning is that caffeine can constrict the blood vessels of the mother, meaning the baby could absorb less nutrition, Marks, a Boston University School of Medicine graduate, said.

The evidence behind the way in which caffeine transfers to the fetus is clear, but studies focusing on Marks’ three concerns are complicated.

In terms of a risk of miscarriage, the studies “were retrospective, meaning that they asked the moms, based on what they recall, how much caffeine they drank in pregnancy,” Marks said. The conclusion was that there is a potential correlation between “increased risk of miscarriage with increased caffeine use.”

During prospective studies, in which researchers actively followed pregnant people throughout their pregnancy, the results “showed that no matter what the dose of caffeine was,” there was no indication of a higher risk of miscarriage, Marks said.

The same goes for early deliveries.

“No matter the dose of caffeine, it has not been shown to affect preterm birth or preterm labor,” the OBGYN said.

One problem in getting a uniform recommendation on caffeine is that research is difficult to perform.

A typical study of this nature would be highly regulated, with one group receiving a set dose of caffeine daily, for example, while another group would be the control, consuming no caffeine. The concern with this is , as explained by Marks, “there’s, unfortunately, a lot of ethical issues with regards to doing these types of trials on pregnant women.”

That means the current caffeine guidelines are primarily based on expert opinion or these retrospective studies, which are also faulted because of the difficulty of precisely tracking a person’s caffeine intake.

Marks said pregnancy-related information is not supported by evidence of the same quality “that we have when we’re studying many other medical conditions.”

Marks offers general guidance to her patients: “Take care of your body, and if you drink a cup of coffee every day, you can go ahead and do that, but this is probably not the time to start drinking a few espresso shots per day.”