Kidney stones during pregnancy are rare. However, they impact roughly 1 in 1500 pregnant women and are a common cause of non child birth related abdominal pain during pregnancy.

Women go through major changes in their renal tract during pregnancy. Significant dilation occurs in the pelvic region and their ureters (pathways from kidneys to bladder- see photo below) also expand. Additionally, Progesterone (a hormone released by the ovaries) relaxes muscles and slows down the natural-involuntary constriction/relaxation of the urinary tract that typically is responsible for moving urine out of the kidneys to the bladder and out of the urethra ¹. Blood flow and the rate of filtered fluid through the kidneys both also increase by over 50% during pregnancy ⁶.

This up-tick in flow leads to increased urinary excretion of calcium, uric acid, sodium, and oxalate, all of which are stone promoting (lithogenic) ^7,8. To further complicate things, calcium reabsorption is also reduced during pregnancy due to suppression of the parathyroid hormone. These changes, combined with slower urine movement through the urinary tract due to the Progesterone mentioned above, lay the foundation for stone formation during pregnancy.

In the general population, calcium-based stones account for over 80% of kidney stones. Calcium-based stones are also the most commonly formed stones during pregnancy ^10,11. However, up to 74% of pregnant women with kidney stones have calcium phosphate stones. This is in contrast to the general population where calcium oxalate stones are more common. The prevalence of calcium phosphate kidney stones over calcium oxalate kidney stones in pregnant women is thought to be related to the alkaline pH of urine that women experience during pregnancy and the increased excretion of stone promoting minerals as mentioned in the previous paragraph ^11,12.

The incidence of kidney stones in pregnancy is quoted to be roughly 1 in 1500 ^9,17,18. Kidney stones also appear to be more common in women who have had more than one child with 80-90% of kidney stones occurring in the second or third trimester ^19-22. Kidney stones are found twice as often in the ureter (pathway from kidney to bladder- see photo above) as stones found in the kidneys during pregnancy ²⁰. And, according to the most recent statistics, women experiencing kidney stones during pregnancy are more likely to be Caucasian and have a history of renal disease and hypertension. A quarter of these women also will have had previous kidney stones ^20,23,24.

For most pregnant women, their realization of the kidney stone(s) presents itself as severe flank pain in the area surrounding the kidneys with pain radiating toward the groin ²⁵. It is also common for nausea and vomiting to occur. Most women will also experience painful urination as the stone makes its way from the kidney through the ureter to the bladder. Once in the bladder, they will experience a sensation of pressure and the urge to urinate will also increase as the body attempts to remove the foreign object (the kidney stone).

One concern that women must be aware of is that kidney stones may also present themselves as pre-term labor or as contractions ^17,19. In one study, nearly 28% of women were incorrectly diagnosed with afflictions ranging from appendicitis to diverticulitis to placental abruption ²⁰.

Presence of kidney stones in pregnant women has been associated with a significant increase in the risk of the following conditions:

• Recurrent Miscarriage: three or more consecutive miscarriages.
• Mild Pre-eclampsia: condition during pregnancy characterized by high blood pressure.
• Chronic Hypertension: long-term high blood pressure
• Gestational Diabetes Mellitus: a form of high blood sugar affecting pregnant women 
• Caesarean Deliveries: procedure where baby is delivered through an incision into the mother’s abdomen (belly) and uterus (womb). Commonly referred to as a “C-Section.”

Kidney stones have also been associated with premature rupture of membranes in one study ²³. Rates of premature births in conjunction with kidney stones have been cited between 2.5-40% ^{17,18,20,23,27}. This is a pretty big range and findings have not been consistent in studies. Since data is conflicting amongst different studies, the true risk of kidney stones during pregnancy is difficult to ascertain.

If you are pregnant and are concerned that you may have kidney stones, a dipstick analysis of mid-stream urine should be performed to look for underlying infection. Urine with a pH of greater than 7 is considered to be alkaline and may suggest infection with a urea-splitting organism (these are the bacteria that we discussed in our last post about Struvite Kidney Stones). Urine with a pH of less than 5 is acidic and may be associated with uric acid stone creation. Additionally, if the dipstick test comes back positive for nitrites, your doctor should perform a urine culture and send it off for analysis to determine if an infection is present or if there is any microorganism involvement (bacteria).

Your doctor should also check your blood for a anemia, kidney function, and any abnormalities in electrolytes (including calcium). If increased serum calcium levels are observed, your doctor should investigate for Hyperparathyroidism (increased levels of parathyroid hormone in body which is responsible for regulating blood calcium levels).

Unfortunately, the use of traditional kidney stone scanning technology such as CT scans and X-Rays are discouraged during pregnancy due to the presence of ionizing radiation’s impact on the fetus. The use of Ultrasound equipment is safe. But, Ultrasounds have poor sensitivity when it comes to kidney stone detection ^19,20,35-37. One way to improve detection rates with Ultrasound technology is to have the scan conducted trans-vaginally (transducer inserted into the vagina) ⁴¹. Traditionally, Ultrasounds are conducted trans-abdominally (transducer used outside of the body over the abdomen). Trans-vaginal scans are reported to be roughly 7 times more effective than trans-abdominal.

Another potential option for kidney stone detection while pregnant is through the use of magnetic resonance imaging (MRI), commonly referred to as magnetic resonance urography (MRU) when related to the urinary tract. An MRI uses electromagnetic radio waves rather than ionizing radiation (like with X-Rays and CT Scans). No harmful effects to the fetus have been reported. However, it is suggested to be avoided during the first trimester ⁴⁸. One downside to the use of MRI technology when scanning for kidney stones is that the scan does not specifically identify kidney stones. It merely suggests certain features that may suggest the presence of a kidney stone ⁵⁰. Kidney stones often appear as signal voids (see photo below).

The lack of accurate scanning technology and limited treatment options leaves doctors and the pregnant women dealing with kidney stones in a difficult situation. Because of this, most doctors choose a course of inaction due to the potential complications of action. Fortunately, roughly 68% of stones less than 5mm in size will be passed spontaneously within 4 weeks. Larger stones (5-10mm in size) also have a decent chance of passing spontaneously at a rate of roughly 47% ^31,56,57. We will discuss stones that are too large to pass on their own below.

The best course of action relating to kidney stones during pregnancy is always going to be prevention. But, often times, we don’t know what we don’t know until we... well, know. So, let’s discuss a few topics key to the management of kidney stones in general and their implications during pregnancy:

1. Hydration: This is one area that is universal and will not impact pregnancy. The more hydrated you are, the better chance you have at not forming kindey stones. Urine should be clear to a slight yellow tint at the most (see photo below).

• 
• The more water (H²O) in your system, the better chance this molecule has at binding with the major stone forming molecules such as oxalate, phosphate, and uric acid and simply pass them out with your urine. If you are dehydrated, these molecules tend to stack upon each other and turn into kidney stones. STAY HYDRATED! This goes for before, during, and after pregnancy. 
• Pain Relief: Your willingness to accept pain medications and/or the type of pain medication will be directly correlated to your views on the impact of said medication on your developing child. Generally, it is discouraged to take pain medications during pregnancy due to the potential implications for the fetus.

• However, some medications such as Acetaminophen and even Opiods, are generally considered “safe” during pregnancy. We say “safe” because your personal view point on medication/drugs/pharmaceuticals will sway this one way or another as mentioned previously. Unfortunately, most find acetaminophen ineffective in managing pain of kidney stones (pregnant or not).
• Opioids are VERY effective for pain. But, again, if you prefer a more natural approach- you will most likely shy away from these. We will defer further commentary here as to the options and urge a conversation with your doctor regarding the risks.
• Inflammation: When your body is dealing with a kindey stone, inflammation is rampant in the urinary tract. And, this makes sense, as your body is trying to rid itself of a foreign object. However, immflamation slows everything down when it comes to passing a kidney stone. In order for kidney stones to pass, the stone requires a free-flowing path. Or, at least a path with the least amount of resistance possible. Just as with pain medication, your view point for or against anti-inflammatory medication will impact your decision regarding this particular facet of kidney stone management.

• Just like for pain relief, Acetaminophen is considered “safe” and can also help decrease inflammation. This is one use case where this medication may prove of some use; as it typically falls short on the pain management side for kidney stones.
• Unfortunately, many of the potent and natural herbal remedies for inflammation are generally regarded as “un-safe” for use during pregnancy. 
• Urine Flow: Increasing the rate of urine flow is key to kidney stone passage as it will speed up the stone’s movement. Low urine flow will not create adequate pressure to prompt the stone to move. You might think that keeping the stone where it is would be a good thing. But, it isn’t. A stationary stone can cause a whole host of other complications that are best avoided (pregnant or not). Increased urine flow can be accomplished two ways. First, through drinking more water and second through the use of diuretics.

• For the general population, utilizing both increased fluid intake and a diuretic will exponentially speed up kidney stone passage. However, for pregnant women, the use of a diuretic (pharmaceutical or herbal) is generally not recommended. The implications with a pharmaceutical option should be obvious to those concerned (un-natural/chemical/etc) and herbal options are also discouraged due to other potential interactions with the pregnancy.
• So, our suggestion would be to adopt the increased water consumption option. Getting on a schedule can be very helpful with this (for example: setting a time for every hour where you consume an 8oz glass of water during waking hours- please note that ounces consumed per hour should vary with relation to the size of your body).
• Citrate: In addition to increased water consumption, adding naturally occurring citrates to your diet will most likely be the most impactful thing that you can do prior to and during your pregnancy with regards to kidney stones. We say naturally occurring citrates because citrates can come in many forms. But, not all are created equal. We recommend using the juice of 1-2 whole organic lemons (because they’re sweeter than conventionally grown lemons) to 16oz of water daily. This can be done with the juice of one lemon consumed in the morning and one in the evening.

• Lemon juice from bottles, concentrates, or powders (freeze-dried raw powders are ok) are not recommended as these have been pasteurized and the levels of citrate have been decreased substantially and are not as bioavaiable.
• Same thing applies to citrate supplements such as magnesium citrate, calcium citrate, and others. When citrates are present in the urine, they bind with all of the lithogenic (stone forming) minerals in the body and simply pass in the urine. Look at citrates as a booster to proper hydration. Water (H²O) molecules will take one portion and citrate takes the other. In essence, spreading the load when it comes to preventing kidney stone crystals from forming. Lemons are completely safe to consume during pregnancy and also have added benefits when it comes to kidney stones:

• Acidity can help break down and erode any current kidney stones
• Lemons have anti-inflammatory properties that can assist with pain relief and reduce inflammation in the urinary tract.

To help summarize the previous section and put it into context for pregnant women who may be currently dealing with a kidney stone, we recommend increasing water intake (to the point of clear to slight yellow tint-see above chart) and adding naturally occurring citrate to your diet. If you utilize these two suggestions, you will put yourself in the best position to deal with your kidney stones in as natural of a fashion as possible with the least potential impact to the fetus. 

Now, for any pregnant women with stones that are too large to pass on their own (typically 10mm or larger or Staghorn structure) or with stones that are causing an obstruction, a more active management plan may be required to solve the issue. An estimated 25-40% if pregnant women will require active intervention of some sort ^17,19-21,23. We will provide a brief description of the current options below. Please note that the following is best discussed with your doctor, urologist, obstetrician, anesthetist, and neonatologist team due to the complicated nature of this type of invasive interaction during pregnancy.

• Ureteral Stent: insertion of a stent (SEE BELOW PHOTO) into the ureter to temporarily open the passage for the stone to travel to the bladder and out of the body. Typically performed under local anesthesia. 

• Percutaneous Nephrostomy (PCN): creates a temporary diversion of urine through a tube inserted directly into the kidney. Typically performed under local anesthesia. (see photo below)

• Ureteroscopic Stone Removal (URS): surgeons use an endoscope in combination with either a laser or ultrasonic lithotripter (concentrated sound waves to break up stone) and a retrieval basket to remove the stone(s). A stent is typically inserted during surgery to encourage any remaining fragments to pass freely. URS may be performed under general or spinal anesthesia or even sedation. (see photo below) 

To conclude, diagnosis and treatment of kidney stones during pregnancy is a complex problem. Risks to the developing child from ionizing radiation and invasive intervention procedures must be balanced with clinical care for the mother. Ideally, the mother dealing with kidney stones during pregnancy would have a team consisting of medical professionals from every area of practice related to her situation. 

Prevention is the key though. So, start early. Especially if you have formed kidney stones in the past. Ensuring that your body is properly hydrated will go a very long way. And, adding in naturally occurring citrates will help boost prevention. 

For more information, please reach out to us directly or consult your physician. 

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