Pregnancy health

This is why you shouldn’t take too many antacids during pregnancy

I had no idea what caused my frightening symptoms. Then I put it all together.

This is why you shouldn’t take too many antacids during pregnancy

Photo: iStock Photo

Last winter I had a few weeks of stomach cramping that I chalked up to an irregular menstrual cycle. When I woke up one morning with intense aching and throbbing in my groin and back, I thought this must be one raging Aunt Flo and the blood in the toilet seemed to confirm it. But as the pain became unbearable, I knew something was really wrong.

Within hours, I was on all fours in a hospital emergency room, bellowing like an injured animal, fighting what felt like contractions not that different from those I’d experienced with the unmedicated childbirths of my two young daughters. Only this was actually worse, with the added vomiting and terrifying uncertainty about what was happening to me.

After blood tests and an ultrasound, the doctor finally figured out what was causing the extreme pain: a kidney stone. Three rounds of morphine later, I was sent home with a prescription for Percocets to take until the stone could be removed, and the lingering question of why, at 39 and in perfect health, I had developed a kidney stone.

Kidney stones are small, jagged masses of salts and minerals that form inside the kidneys and may travel down the urinary tract where they cause severe pain in the lower abdomen, groin or back, and sometimes lead to nausea and blood in the urine. They can range in size from a tiny speck to a golf ball.

My ultrasound showed that mine was six millimetres and stuck in the ureter tube that goes from the kidney to the bladder. I learned that stones larger than five millimetres typically don’t pass on their own. Depending on the size and position of the stone, passing one—or having one trapped in your urinary tract—can be excruciating and is one of the most common reasons for ER visits.

About one in 10 Canadians will have a kidney stone at some point in their life, according to the Kidney Foundation of Canada. The causes are complicated, but you’re more likely to experience certain types of stones if you don’t drink enough water (at least eight glasses a day) or if you have an excessively imbalanced diet, with too much salt, meat and processed foods. In general, it is advised to drink lots of fluids and eat a balanced diet to prevent kidney stones.

If your kidney stone is caused by too much calcium—the most common type—you may also be advised to reduce oxalates from foods like beets, nuts and chocolate. Oxalates prevent calcium from being absorbed by your body, causing it to spill into your urine. Doctors don’t usually recommend cutting natural sources of calcium from your diet, but will advise people who are at risk for kidney stones to stop using calcium supplements.

I didn’t have any known risk factors for kidney stones (follow-up tests confirmed it), and my diet didn’t have any red flags, but I had given birth to my second daughter 14 months earlier and spent the latter part of my pregnancy popping calcium-carbonate antacids (Tums) to deal with terrible heartburn. They seem fairly innocuous as over-the-counter chewable tablets that both look and taste like those sweet candy hearts you get on Valentine’s Day.


To be clear, I took a lot of them, up to the maximum dosage of six extra-strength tablets. That amounted to 1,800 mg of calcium—on top of my prenatal vitamin—on a daily basis in the third trimester of both pregnancies less than two years apart. The third trimester is when pregnancy heartburn and reflux gets real, as hormonal changes cause the valve between your esophagus and stomach to relax, allowing acid to escape into your chest and throat.

As your baby and uterus grows, there is also more pressure on your stomach, which causes stomach acid to back up. In later stages of pregnancy, many women can’t digest a single meal—no matter how small, non-spicy and non-acidic—without an irritating and burning sensation. But calcium carbonate can help take that edge off.

My urologist and kidney stone surgeon, Peter Vlaovic at Michael Garron Hospital in Toronto, says the general guidelines are that calcium consumption should not exceed 1,000 milligrams a day for pregnant or lactating women ages 19 to 50. He says it’s conceivable that I could have been working on that kidney stone for months, or even years between both my pregnancies, before it became a problem.

“That could definitely have something to do with it,” he said.

Jordan Weinstein, the medical director of the kidney stone prevention clinic at Toronto’s St. Michael’s Hosptial agrees. “It’s pretty clear that if you load up on calcium, it is a risk for kidney stones. However, if you restrict calcium, it is also a risk for kidney stones, which seems like a bit of a paradox.”


Weinstein explains that if you cut calcium out of your diet, you lose an important binder of oxalate in the gut—and then the oxalate gets excreted into the urine and contributes to kidney stone risk. “It’s a bit like the Three Bears,” says Weinstein. You have to get the balance of calcium and oxalates just right.

Weinstein notes that taking extra vitamin D, which you likely have in your prenatal vitamin, also helps your body absorb extra calcium. So taking a vitamin D supplement (yup, I did that, too) may increase the risk of stones, so talk to your health care provider about any supplements you’re taking.

While kidney stones are actually quite rare during pregnancy—the published numbers are only one in 2,500 to 3,000 women—loading up on calcium supplements, including Tums and Rolaids, could certainly cause problems down the road.

“Remember that kidney stones don’t generally form overnight,” says Weinstein. In fact, if you have a tendency to form stones, most women get a holiday from them during pregnancy, because the urinary tract dilates in response to pregnancy hormones. “It allows stones more easily to pass and some women aren’t even aware that they’ve passed them,” he says.

So you could not know you have kidney stones until you’re no longer pregnant.


The problem with taking calcium during pregnancy A couple months after my kidney stone attack, I had it surgically removed. (Luckily it had “settled” in that time so it didn’t cause incessant pain.) Vlaovic had analyzed the stone and found it was caused by an excess of calcium or oxalate in my urine.

When I called him for this story, he pulled up research that shows that pregnant women tend to leak more calcium in their urine anyway. “You’re raising a valid concern there,” says Vlaovic. The research showed that supplementing calcium—with antacids or otherwise—in well-nourished women during pregnancy is not a good idea.

So, why aren’t there warnings about side effects? Before I started taking the antacids, I had called the Motherisk helpline, which gave me the go-ahead to use them as recommended, as they have no known health risks to the fetus. But one small study by the Cleveland Clinic Lerner College of Medicine in 2015 showed that taking calcium supplements (which is basically what calcium-carbonate antacid tablets are) may worsen stone disease for patients who are known to form kidney stones.

Other studies have also questioned the use of calcium-carbonate for heartburn in pregnant women. “Caution must be exercised regarding the unrestricted use of calcium-carbonate supplements, generally considered ‘safe’ in pregnancy,” say the authors of a 2013 case study from Mount Sinai Hospital and the University of Toronto, referring to the fact that pregnant women tend to excrete more calcium naturally.

They added that, if small amounts of calcium-carbonate do not alleviate reflux symptoms, pregnant women should not hesitate to take those histamine-2 blockers (H2 blockers like ranitidine, under the brand name Zantac) or proton-pump inhibitors (PPIs such as omeprazole, under the brand name Losec) that have proven to be safe.


One other reason you definitely don’t want to overdo the calcium—pregnant or not—is a rare but frightening condition called calcium alkali syndrome (CAS)—which can lead to kidney failure, as well a slew of other symptoms including vomiting and dehydration.

By now it’s obvious that if I was taking antacids for heartburn that often, I should have been seeing a doctor about it. Amanda Selk, an OB/GYN at Women’s College Hospital, explains, “The [Tums] label says don’t take it for more than two weeks unless a physician tells you to. The problem is, “I don’t know that everybody always reads or asks, which is an issue with over-the-counter drugs in general.”

According to Selk, calcium carbonate is not a great antacid to begin with, so many women will be better off taking something stronger. The bottom line is that, if heartburn during pregnancy is something you can’t manage or prevent with your diet, it’s better to try a combination of treatments, versus taking too much of one thing.

What really does work?

In Selk’s practice, if a patient needs relief for heartburn or acid reflux, she starts with small doses of two to four tablets of Tums a day depending on the strength, but if that’s not working well, she’ll advise stepping up to something like liquid Gaviscon (an antacid suspension made of aluminum hydroxide and magnesium carbonate instead of calcium), followed by a H2 blocker like Zantac, which is also available over the counter.

Lastly, in more severe cases, she might prescribe a PPI such as Losec. Although all those options are considered safe during pregnancy, they have also all been linked with kidney issues. And, as always, it’s important to talk to your doctor about starting any medications, and which options are safest for you.


Looking back, self-medicating on over-the-counter calcium-based antacids for my pregnancy heartburn probably wasn’t so smart. I never cleared it with my family doctor. I was reluctant to take a stronger medication or prescription drug, and I assumed that because I was just taking vitamins and minerals versus a drug, I could do no harm, to myself or my baby.

“It’s a common misconception that natural is safe and that pharmaceuticals are dangerous, whether in pregnancy or outside of pregnancy,” says Weinstein.

Now that I have a history of kidney stones, I definitely won’t be reaching for calcium carbonate if heartburn ever becomes an issue again.

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This article was originally published on Apr 11, 2018

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