TL;DR Some studies show that ingesting caffeine during pregnancy can cause harm to the baby, while others weren't able to establish a direct link between caffeine and adverse effects like a miscarriage. While the jury's still out on this one, there are precautions to take and key things to remember when consuming caffeine while on the way.
Pregnant ladies may be going through A LOT of changes (such an understatement, we know).
This is probably true not just with their body (physical and physiological), but also in their diet. There’s a lot of foods and beverages to avoid during pregnancy, which is a tall order for a lot of people! 
We’re going to try to answer this million-dollar question by putting together the various research and studies we’ve found on the topic and try to help you ladies come up with not just an answer, but a solution.
What a recent academic 'review' article says (and why there’s no cause for panic)
An academic review published in BMJ Evidence-Based Medicine by a psychology professor in Iceland caused a bit of a stir in August 2020. Professor Jack James from Reykjavík University reports in the review that "maternal caffeine consumption is reliably associated with major negative pregnancy outcomes," concluding that caffeine should be avoided by pregnant women at all cost.  The article covered “37 observational studies and meta-analyses” that found six negative pregnancy outcomes due to caffeine consumption: miscarriage, still birth, low birth weight or small for gestational age, preterm birth, childhood acute leukemia, and overweight/obese baby. 
Now if you’re a pregnant woman who loves her caffeine fix, or a coffee-lover who’s been trying, there’s no need to panic yet.
The coffee industry has dismissed this study as purely observational and not having enough evidence to prove cause-and-effect.
Epidemiologist Gideon Meyerowitz-Katz from the University of Wollongong in Australia provided an analysis of James’ review in a Twitter thread and suggested that the conclusions made are misleading. Specifically, the problems he highlighted are as follows:
James’ narrative review is based on an existing medical literature, NOT on new findings from a recent clinical study. That means it is purely based on opinions of the author from an existing study, and thus shouldn’t be regarded as “new evidence.”
The conclusions James made in the reviews did not align to the original conclusions of over 40 studies he covered. For instance, James linking caffeine intake to miscarriage is misleading. The original conclusion states there should be *higher* levels of coffee consumption, i.e. 400mg a day, for it to happen.
Table 2 in James’ review contained erroneous figures.
Meyerowitz-Katz along with other researchers and experts who have done studies on the topic suggest that caffeine could have adverse effects during pregnancy when taken in high amounts.
In fact, the World Health Organization acknowledges the same and recommends 300mg a day or less of caffeine should be fine for pregnant women. That’s equivalent to two cups of mid-strength java fix.
Caffeine effects during pregnancy
While research and studies on the topic are conducted quite exhaustively, they're also widely conflicting.
Some studies say that caffeine is not at all good for mum and the bub, as it results in these adverse effects:
Caffeine has stronger effects in pregnant women than those who aren’t. As a stimulant, caffeine’s psychoactive effects – those that make you feel wired up and jittery – may be observed more among pregnant women.
Having a bun in the oven slows down the body’s ability to break down caffeine, so higher levels of caffeine stay longer in the bloodstream. The farther along you are, the longer caffeine stays in your system, and the more intense its effects are in your body. 
Caffeine may damage babies' liver. Based on a recent study published in July 2019, caffeine intake that's equivalent to two or three cups of coffee caused pregnant rats to give birth to "offspring with lower birth weights, altered growth and stress hormone levels, and impaired liver development."  The study didn't involve people though, so it's still inconclusive in this sense.
Babies can’t process caffeine properly yet. When caffeine enters your system, it crosses the placenta into the amniotic fluid, as well as your baby's bloodstream. Your body may be able to digest it – albeit longer than usual – but your baby's still developing body may have a harder time breaking it down.  
Because of this, the caffeine stays longer in the baby’s system, resulting in the following:
baby’s heart beating unusually faster, which can lead to arrhythmia or irregular heart rhythm (read: potentially dangerous!)
baby developing caffeine dependence. When they’re born, they can be very irritable, showing signs of withdrawal
Risk of miscarriage. A study from the National Institutes of Health and Ohio State University linked a couple’s consumption of more than two caffeinated beverages a day to a risk of miscarriage.
A woman is more likely to miscarry if she and her partner drink more than two caffeinated beverages a day on the weeks leading up to conception.
Similarly, women who drank more than two daily caffeinated beverages during the first seven weeks of pregnancy were also more likely to miscarry. 
Obesity. A 2018 journal published in the BMJ Open reports that going overboard with caffeine during pregnancy may lead to obesity. Specifically, too much caffeine among women on the way is “is associated with a higher risk of excess infant growth and of childhood overweight, mainly at preschool ages.” 
Impact on brain functions. According to Dr. De-Kun Li , a reproductive and perinatal epidemiologist in the Division of Research at Kaiser Permanente Northern California, caffeine has adverse effects to the development of the hypothalamus-pituitary axis in the brain, responsible for regulating many of the hormones needed for childhood growth and development.
"We know that caffeine affects the neurotransmitters that affect the brain, and we know that anything that happens during the fetal period will be amplified and could be long-lasting," Dr Li said. 
Caffeine may cause iron deficiency. Caffeinated beverages contain compounds that prevent the body from absorbing iron properly. Women on the way need to keep this in check as many tend to be iron deficient during pregnancy. 
But some studies beg to differ …
While the above studies emphasize the adverse effects in consuming caffeine during pregnancy, some reports seem to say "not really":
Don’t blame it on caffeine. One study found that having more than three cups of coffee in a day did NOT increase miscarriage. Oddly enough, drinking the same amount of decaf was linked to higher risk of spontaneous abortion, which is 2.4 times higher. 
Researchers have varying findings. An evidence review conducted in 2010 by researchers at the University of Oklahoma Health Sciences Center and Harvard Medical School went over ALL research done on the topic since 2000.
It’s all inconclusive!
“[T]he evidence for an effect of caffeine on reproductive health and fetal development is limited by the inability to rule out plausible alternative explanations for the observed associations.” 
Cultural than scientific. Here’s something interesting from Princeton sociologist Elizabeth Mitchell Armstrong, author of Conceiving Risk, Bearing Responsibility: Fetal Alcohol Syndrome and the Diagnosis of Moral Disorder.
She says that all this talk about pregnant women not allowed to have their caffeine fix may be due to cultural norms and cognitive biases more than scientific evidence itself.
“We expect mothers to be completely self-sacrificing for the sake of their children,” she explains. “This performance of maternal sacrifice during pregnancy—whether in the form of giving up caffeine, or alcohol, or some other form of abnegation—is expected of pregnant women today not only as a route to better fetal health, but as a means of demonstrating their moral fitness to become mothers.”
So what’s a mama got to do?
The American Pregnancy Association suggests that it's better to be safe than sorry:
“Due to conflicting conclusions from numerous studies, the March of Dimes states that until more conclusive studies are done, pregnant women should limit caffeine intake to less than 200 mg per day. This is equal to about one 12 oz cup of coffee.”
However, the latest amount that’s considered safe for pregnant women is 300 mg caffeine a day, based on a 2017 study. 
It all boils down to knowing the caffeine content, especially since caffeine is not only found in coffee but in many different products as well.
Here’s an infographic from The Bump that shows the amount of caffeine found in different products: 
If you must quit caffeine (and feel like it’s going to be an ordeal), remember that you don’t have to do it cold turkey. Here are some tips that can help you steer clear from caffeine (at least for now):
Go decaf. Consider switching to decaffeinated drinks, which usually have small amounts of caffeine to none. You can mix it up with regular coffee or more milk.
Slowly but surely. Go easy on quitting so you can lessen the impact of potential withdrawal symptoms.
Switch to herbal teas. Some teas have no caffeine but it’s always good measure to check the content. Here’s another infographic from The Bump as reference:
Ninja caffeine is ninja. Caffeine is not only consumed orally. It can also be ingested topically. Like what, you ask.
Three words: cocoa butter lotion.
This is commonly used by pregnant women to prevent stretch marks. A 2006 study found a lowered risk of fetal heart arrhythmias in babies with moms who didn’t use cocoa butter lotion while on the way. 
Multivitamins help.There was some good news in the study, however, because the researchers found that there was a reduced risk of miscarriage if women took a daily multivitamin. During the time before conception, the hazard ratio was only 0.45—what the press release calls “a 55-percent reduction in risk for pregnancy loss. Women who continued to take the vitamins through early pregnancy had a hazard ratio of 0.21, or a risk reduction of 79 percent.”
Our advice is pretty simple. Have a caffeine fix within the prescribed limits of WHO and the rest of experts, which is 300 mg or less. Try at most 2 cups of medium strong coffee a day or a caffeine mint of 40 mg apiece.
When in doubt, consult your doctor or healthcare professional to find out the effects of caffeine in your own specific situation.
Or you can just err on the side of caution and ease off on caffeine altogether.
Remember, you can always go back to your favorite café after this wonderful journey!
Erectile dysfunction. In combination, those are two of the ugliest words known to man. But can caffeine help you get it up?
Science hasn't found the definitive answer to this question, but one study concluded that fewer men who consume caffeine have problems performing. The study said:
Caffeine intake reduced the odds of prevalent ED, especially an intake equivalent to approximately 2-3 daily cups of coffee (170-375 mg/day). This reduction was also observed among overweight/obese and hypertensive, but not among diabetic men. Yet, these associations are warranted to be investigated in prospective studies