The Kidneys During Pregnancy: How Your Kidneys Change and Work During Pregnancy

Why You Should Take Special Care of The Kidneys During Pregnancy...

"The Natural Women's Health Guide... to Pregnancy - BUY HERE!"

The kidneys are extremely important during pregnancy. Most women have had at least one experience with a urinary tract infection in their lives (if you’re one of the few who hasn’t, lucky you!), and as most of us know, a UTI isn’t something to let linger for too long. It’s uncomfortable, and if a urethral or bladder infection spreads to the kidneys, it can be serious. But, otherwise, most of us don’t spend a lot of time thinking about or caring for our kidneys unless they speak up and make some noise (in the form of an infection or kidney stones, for example). 

During pregnancy, however, it’s wise to pay attention to the kidneys from the very beginning. Take care of your kidneys. They’re more important than you think they are, especially at this time, not only in regard to your health, but also for the health of your unborn child. 

The kidneys change a lot during pregnancy. In fact, they grow in size up to 30%, and may even get 1-1.5 centimeters longer! The kidneys revert back to their original size about 1 month after pregnancy, but these changes are testament to the fact that these two organs are indeed extremely important during pregnancy. Besides the uterus, they’re the only other organs in the body that will grow in this way when a woman is pregnant. This is largely due to the increased blood flow that they must filter at this time.

This change might seem like it comes out of the blue, but in reality, women’s kidneys are in a constant state of change during every menstrual cycle. The function of the kidneys changes according to where a woman is at in her cycle, which precipitates these changes that occur during pregnancy. The hormonal changes happening in a woman’s body during her cycle and the changes that occur in the kidneys are, in fact, intimately intertwined with one another. For example, during the mid-luteal phase of the menstrual cycle, a time when a woman’s progesterone levels will naturally be higher in response to the potential for pregnancy, the glomerular filtration rate (GFR) and renal plasma flow (RPF) will be higher than usual, as will cardiac input. 

To clarify: glomerular filtration rate (GFR) refers to how much blood is passing through the kidneys’ glomeruli (little filters that process waste and excess fluid from the blood) every minute. Renal plasma flow (RPF) refers to the volume of plasma (a component of blood) that’s passing through the kidneys each minute. 

Thus, a higher RPF means that the kidneys have more to filter, and the higher GFR rate is indicative of the increased filtration that the kidneys are actually doing. 

When a woman gets pregnant, after ovulating, her GFR and RPF rates remain higher throughout the gestational period, with some variability. At 4 weeks of pregnancy, her GFR will have increased by 20%, and at 9 weeks of pregnancy, her GFR will have increased to 45%. Then, there’s a slight decrease that happens, and on average, at-term a woman will have a GFR that’s 40% higher than normal. One month after giving birth, the woman’s GFR levels will have returned to their normal levels. 

Until the end of the 1st trimester, however, around 12 weeks of pregnancy, the woman’s RPF rate will exceed her GFR rate. This means that the amount of plasma passing through the kidneys is higher than usual, but the filtration rate for this extra plasma is still too low to actually keep up with the body’s filtration needs. Theoretically, then, during the first trimester of pregnancy, the woman’s kidneys ultimately struggle to keep up with the increased blood and plasma filtration needs of her body. 

For reference, plasma volume generally increases by 6% by the end of the first trimester, by 18% during the second trimester, and by 42-48% during the last trimester of pregnancy. Blood volume increases by up to 50% by the end of pregnancy. 

The hormone relaxin, which is produced in the corpus luteum, placenta, and decidua (the modified mucosal lining of the uterus that forms in order to protect the fetus), also may play a role in increasing RPF and GFR during pregnancy.

Despite these increases in blood and plasma volume, however, it’s normal for a woman’s blood pressure to be somewhat lower than average throughout pregnancy. This is due to the actions of a system known as the Renin-Angiotensin-Aldosterone system (RAAS), which works somewhat differently during pregnancy than normal. And, it all depends largely on the kidneys to function correctly. This system is vital for the management of blood pressure regulation, blood volume, sodium resorption, water retention/resorption, and vascular tone. 

Below is an outline of the RAAS system (this is very technical stuff, but it's helpful to understand at least the basic overview of what's happening in your body so that you can treat yourself if something goes wrong): 

1. The kidneys release renin, an enzyme, into the bloodstream in response to a drop in blood pressure. 
2. The renin travels to the liver, which produces angiotensinogen (a protein), and splits this angiotensinogen protein into parts. One of the parts is the inactive hormone called angiotensin-1. 
3. In order to be activated, the angiotensin-1 now travels through the bloodstream back to the kidneys, and also into the lungs. In one or both of these locations, angiotensin-1 is converted to its active form, angiotensin-2, by angiotensin-converting enzyme (ACE).
4. Angiotensin-2 then can cause the muscles in the walls of the arterioles (tiny blood vessels) to constrict, which thereby increases blood pressure. The angiotensin-2 also triggers the adrenal glands to release aldosterone and the pituitary gland in the brain to release vasopressin / antidiuretic hormone (ADH).
5. Aldosterone and ADH then work together to tell the kidneys to retain sodium; aldosterone also tells the kidneys to excrete potassium in the urine. So, these two hormones ultimately regulate the sodium-potassium balance in the blood. 
6. When blood sodium levels then increase, this causes the body to retain water, which increases blood volume and also increases blood pressure (so, angiotensin-2 increases blood pressure in one way in Step 4, while aldosterone and ADH increase blood pressure levels in a different way here). 

During pregnancy, there are some changes that occur in this system. First of all, more renin is produced during pregnancy by the ovaries and decidua. In addition, the increased levels of estrogen that occur during pregnancy also stimulate the liver to produce more angiotensinogen. Aldosterone levels have also been seen to be higher during pregnancy. Theoretically, this combination of factors should mean that vasoconstriction, or high blood pressure, would be more common during pregnancy, but in reality, the opposite is true. There are two reasons for this: 

• Higher-than-normal progesterone levels during pregnancy and increased levels of vascular endothelial growth factor (VEGF)-mediated prostacyclins (these are vasodilators and inhibit blood clotting) contribute to an increased resistance to angiotensin-2 in the receptor sites for this hormone. 

• Angiotensin-2 Type 1 receptors (AT1) are less responsive to signals from angiotensin-2 during pregnancy. 

So, the entire RAAS process ultimately gets slowed down considerably at Step 4, thus making it so when a pregnant woman’s blood pressure drops, it’s less likely that her body will pull it back up to normal levels. But, the system still works during pregnancy, it’s just less efficient, so in a healthy pregnancy, this will manifest as a lower-than-normal but still healthy and safe blood pressure level.

These changes in a woman’s body during pregnancy can explain a lot of her symptoms, especially during the first trimester and the early stages of the second trimester. Because of the increased plasma flow and comparatively lower filtration rate, the pregnant woman’s body is more likely to have toxic buildup in her bloodstream and tissues during the first trimester. This can contribute to fatigue, nausea/vomiting, and other common first trimester symptoms (which can actually, in some cases and ways, resemble a detoxification reaction). During the second trimester, when her kidneys catch up with her body’s filtration needs, these symptoms begin to subside as the toxins are able to be cleared out more effectively. 

The Conditions of Pregnancy Living Database, BETA Release - NOW AVAILABLE! Click here to learn more...

Fetal Kidney Development: A Basic Overview

In order to understand certain aspects of the changes that occur to the kidneys during pregnancy, it can also be helpful to understand how fetal kidney development occurs. There are 3 stages to mammalian kidney development: pronephros, mesonephros, and metanephros. 

The pronephros stage of development occurs about 22 days after conception. This forms a simple tubular system that is relatively nonfunctional and which will disintegrate later on when more permanent structures begin to develop. This system gradually extends down and becomes the mesonephric duct (also known as the Wolffian duct) by around day 28 of gestation. 

The mesonephric duct will eventually form the urinary bladder and the caudal vas deferens and epididymis in the male genital system. Tubules now begin to form during the mesonephros stage of kidney development and begin to excrete small amounts of urine; most of these degenerate, but a few remain throughout the process of kidney development. By 5 weeks of gestation, the ureteric bud will branch out to eventually form the metanephros. 

The metanephros will begin to function around 6-10 weeks of gestation, and will be complete around 36 weeks of gestation. Between 9-10 weeks of pregnancy, the first glomeruli of the kidneys form. At 20 weeks, the fetus begins producing more substantial quantities of urine, and this fetal urine now is a major contributor to the amniotic fluid, contributing approximately 300mL/kg of fetal body weight per day. Between 18-32 weeks, the fetus’ nephrons (kidney cells) multiply and increase in number. Finally, by 32-36 weeks of pregnancy, the nephron development will be complete, and the fetus’ kidneys will be more or less fully functional after his/her entry into the world. 

In baby boys, the mesonephric ducts will move closer together and eventually enter the prostatic urethra, where they’ll form the ejaculatory ducts, the vas deferens, and the seminal vesicles. In contrast, in baby girls, these mesonephric ducts eventually decompose completely due to a lack of testicular androgens (instead, the urogenital system and female sexual organs in baby girls develop in response to the presence of estrogens). The urogenital sinus, a hollow cavity that exists only between weeks 4-7 of fetal development, forms different parts of the male and female urogenital systems. 

In males, the upper urogenital sinus (UGS) becomes the urinary bladder, the pelvic section of the UGS becomes the prostatic and membranous parts of the urethra, the prostate, and the Cowper’s gland, while the phallic section of the UGS becomes the spongy part of the urethral gland as well as urethral glands. In females, the process is different. The pelvic UGS in baby girls first develops into sinovaginal bulbs, which eventually become the inner, inferior two-thirds of the vagina. The female urogenital sinus also develops into the urethra and the vaginal vestibule.

Below is a basic breakdown of how the kidneys develop in the fetus during pregnancy:

• Month 1: The pronephros forms. This consists of 7-10 nephrotomes, which are solid or tubular structures that will later disappear by the end of the first month. 

• Month 2: The mesonephros, and the mesonephric/Wolffian duct, begins forming at the beginning of Month 2. Small tubules begin to form and excrete urine. These include an S-shaped loop with a single glomerulus (filter) and a single Bowman’s capsule (a sac that holds the glomerulus). The urogenital ridge develops during Month 2; this is the precursor to the development of the gonads. The metanephros begins developing at the end of the second month of pregnancy, while most of these aforementioned structures of the mesonephros will disappear by Week 8, though a few will remain for later.
• Month 3: The first glomeruli of the kidneys form, along with the metanephric blastema. The metanephric blastema eventually contributes to the development of structures derived from the ureteric bud, such as the ureters, renal pelvis, collecting tubules, and the major and minor calyces of the kidneys. The metanephric blastema also later evolves into the excretory system, which is composed of excretory tubules, nephrons, the loop of Henle, and Bowman’s capsules. 

• Month 4: The kidneys are now 90% likely to be able to be viewed on an ultrasound. They are continuing to develop toward their final form.

• Month 5: Fetal urine production contributes about 300mL/kg of fetal body weight per day to the amniotic fluid. The fetal nephrons continue developing.

• Month 6: The fetal nephrons continue developing.

• Month 7: The fetal nephrons continue developing.

• Month 8: The fetal nephrons continue developing, but are now mostly developed.

• Month 9: The fetal nephrons continue developing, but are now mostly developed.

Approximately 60% of a child’s nephron development will occur during the last trimester of pregnancy, meaning that kidney development is at its peak during these last 3 months. Infants who are born prematurely or who have a low birthweight thus have been observed to be more likely to have kidney problems or to develop chronic kidney disease (CKD) at some point during their lives. In general, congenital abnormalities of the kidneys and urinary tract are also among some of the most commonly seen out of all the different kinds of congenital abnormalities, with these accounting for about 20-30% of all major birth defects (note that these particular abnormalities are usually detected during the third trimester). 

The Kidneys During Pregnancy in Traditional Chinese Medicine

Traditional Chinese Medicine offers some extra insight into how the kidneys work during pregnancy, and how women can take care of themselves during this time in order to maximize their health and the health of their baby. There are 3 main months of pregnancy that are relevant in terms of the Kidneys: the first month, the fourth month, and the ninth month. 

In the first month of pregnancy, when the baby is conceived, kidney health is especially important as the Kidneys relate to the woman’s ability to actually conceive, and also to the future health of the fetus (since the mother’s and father’s Kidney Essence both contribute to the fetus’ lifelong Kidney Essence at the time of conception). In the fourth month, the mother’s Kidney Essence feeds the fetus directly. Different organs nourish the fetus at different times during pregnancy, but during the fourth month, the Kidneys begin to take on some of this responsibility in order to help the fetus develop its blood vessels; the Triple Burner, however, is the main Channel that nourishes the fetus at this time. Then, during the ninth month of pregnancy, the Kidney Channel is primarily responsible for nourishing the fetus, and the mother’s energy flows along this channel to the growing baby. 

Before continuing onward to how exactly the Kidneys affect the mother and fetus during pregnancy, it’s helpful to understand the basics of how TCM views the Kidneys. 

In Chinese medicine, the Kidneys are the foundation of life, and the source of Essence (Jing), which can also be described in more familiar terms as vital life force or even as DNA. There are 2 kinds of Essence that are relevant to the discussion of pregnancy (and life in general): Pre-Essence and Post-Essence. Both live in and are produced by the Kidneys. Pre-Essence cannot be changed; this is the Essence given to a child/person at the moment of their conception. Similar to genes or DNA, it comes from the mother and father and from the child’s ancestors, and is directly influenced specifically by the mother’s and father’s health at the time of conception. Post-Essence is provided by Spleen Qi, and “supplements” the Pre-Essence. Post-Essence changes throughout life, and can be strengthened and fortified. If a person’s Pre-Essence is weak or somehow problematic, the Post-Essence can be enhanced in order to help the person rebalance and heal from disease. 

The Kidneys are the foundation of life in that they house Essence, but they also are thought to fuel all of the other systems of the body. The Kidney Yin and Kidney Yang are the origin of all of the other Ying-Yang energies in the body, and are considered to be the Primary Yin and Primary Yang in the human body. Kidney Yin and Kidney Yang depend on each other, and if one is deficient, the other is also likely to be deficient. Because of this, deficiencies or changes to the Kidney Yin or Kidney Yang not only affect the Kidneys, but also literally every organ and tissue in the body. 

Finally, Traditional Chinese Medicine organizes the organs of the body into Yin-Yang pairs. These various pairs work closely together in the body and represent different manifestations of cosmic balance in the organ systems. The Kidneys and the Bladder are one of these “couples”; the Kidneys are considered to be Yin and the Bladder is Yang in this coupledom. Together, they govern both water and fire in the body. As an example of their relationship, the Bladder receives Qi from the Kidneys which allows the Bladder to store, transform, and excrete urine. The Kidneys and the Bladder also work with the Spleen, Lungs, and Intestines to regulate the water pathways in the body. 

Essence (Jing), which originates and is stored in the Kidneys, is responsible for a long list of important duties, including: 

• Reproduction
• Growth and development (Essence rules the development of bones, teeth, hair, and the brain during childhood)
• Sexual potency, sexual life, and sexual maturation
• Conception
• Pregnancy
• Menopause
• Menstrual blood / Tian Gui
• Ova creation and development
• Sperm creation
• Constitutional strength
• Vitality
• The ultimate, physical decay of the body
• Immune system function

These responsibilities of the Kidneys are remarkably similar to the responsibilities of Apana Vayu, a type of “wind” classified in Ayurvedic medicine. I’ll talk more about this in a different section, but the important thing to note is that Apana Vayu lives in the pelvic cavity, urinary tract, vagina, and cervix (among other areas nearby), and that it’s responsible for kidney function, as well as for stimulating menstruation, childbirth, libido, conception, and the nourishment of a growing fetus. In both Chinese medicine and Ayurveda, impediments to the Kidneys / Apana Vayu is considered to be a major cause of delayed labor, and stimulation of the Kidney Channel or of Apana Vayu can help speed up / unstick the process of childbirth. 

But now, returning to Chinese medicine…

The Kidneys share some important connections with other organs and tissues in the body, which can help explain certain symptoms and problems that sometimes occur during pregnancy. Below I’ll outline the basics of some of these connections (the Kidneys-Bladder connection is discussed above): 

• Kidneys-Uterus: The Uterus and the Kidneys share an intimate relationship. Weak or deficient Kidney Qi or Kidney Essence can ultimately lead to a deficiency of Qi in the Uterus, which can lead to problems with conception, pregnancy, menstruation, and other women’s health problems specifically connected to the uterus. Blood Deficiency also contributes to problems in the Uterus; note that the Kidneys are indirectly related to Blood Deficiency as well through their connection to Marrow, since Marrow is involved in the production of Blood. If a Kidney problem affects the Marrow negatively, this can also affect the Blood, and then ultimately affect the Uterus. The Uterus stores Kidney Essence, and in this way, Kidney Essence is directly responsible for menstruation, conception, healthy pregnancy, and childbirth. During pregnancy, the uterus is thought of as a Yin Organ since it is a “receptacle” for the fetus. However, during childbirth, the uterus changes its behaviors and becomes a Yang Organ in order to push the baby out of the uterus. When a woman isn’t pregnant, the uterus is empty, and therefore would be considered a Yin Organ; this is of particular relevance since Traditional Chinese Medicine usually views pregnancy to be a more Yang state of being, while women usually operate in a Yin state of being when not pregnant. Because of this, the postpartum period requires special care and attention since the transition from the full, warm Yang state back into the cool, “empty” Yin state can cause sickness if the woman isn’t properly attended to (for example, she’s encouraged to eat light, warm, nourishing foods and to avoid the cold in all forms). 

• Kidneys-Spleen: The Kidneys and the Spleen are close. They are a part of the system that regulates water pathways, and also work together to manage a person’s Essence. The Spleen supports the Kidneys by transforming and “raising” Body Fluids and water to the upper areas of the body when necessary, while the Kidneys support the Spleen by providing Kidney Yang to fuel this particular process. The Kidneys also support the Spleen by warming it to support digestion. 

• Kidneys-Stomach: The Kidneys also warm the Stomach as a part of the process of digestion. 

• Kidneys-Lungs: The Kidneys and the Lungs also work together as part of the process of water regulation in the body. The Lungs are responsible for circulating and pushing down fluids that are processed by the Kidneys. When the Lungs send clean air (Qi / oxygen) to the Kidneys, the Kidneys are responsible for holding this Qi down in order to prevent it from rebelling and flowing upwards, against its natural flow. If the Kidneys are impaired and this Lung Qi flows upward, problems like congestion, breathlessness, asthma, panting, or difficulty breathing can occur. 

• Kidneys-Intestines: The Kidneys and the Intestines are a part of the grouping of organs that regulate water pathways. The Intestines also receive Kidney Yang in order to process and filter Body Fluids.

• Kidneys-Marrow: The Marrow isn’t technically an organ, but it deserves special mention nonetheless (also, in Chinese medicine, Marrow is classified as an Extraordinary Fu organ). Note that in TCM, Marrow includes not only bone marrow, but also the bones themselves, the brain, and the spinal cord. Kidney Essence is thought to be a main contributor in the creation of Marrow. 

• Kidneys-Lower Orifices: There are 9 Orifices in TCM, which include the urethra, anus, eyes, ears, nostrils, and mouth. The Kidneys ultimately are responsible for controlling the Lower Orifices (in addition, the Kidneys are said to “open” into the ears; ear problems are therefore intimately related to kidney function). Problems with Kidney Qi can thus cause problems like incontinence, diarrhea, or spermatorrhea. 

• Kidneys-Hair: The hair is nourished by the Blood, which is partly created by Essence made by the Kidneys. Kidney Essence Deficiency in TCM is associated with a wide range of hair problems. 

• Kidneys-Bones: The Bones are an Extraordinary Fu Organ of TCM. They are nourished by Marrow and Kidney Essence, and therefore their health is both directly and indirectly connected to the health of the Kidneys. Kidney problems can thus result in the development of bone weakness in some cases.

The Uterus in Traditional Chinese Medicine

The Uterus in TCM is called “Bao Gong” or “Zi Gong”, which translates into Chinese as “Palace of the Child”. It is classified as an Extraordinary Organ, which, along with the other Extraordinary Organs, means that it’s characterized by emptiness or hollowness (the other Extraordinary Organs are the Brain, the Marrow, the Bones, the Blood Vessels, and the Gallbladder). The Uterus in Traditional Chinese Medicine refers not only the uterus itself, but also to the ovaries, the fallopian tubes, and the cervix. 

The Ren Mai (the Directing Vessel) and the Chong Mai (the Penetrating Vessel) run through and support the Uterus energetically; these are not primary channels, but rather are two of the 8 extraordinary vessels in TCM. The Ren Mai is responsible for delivering Qi, Yin, and Essence to the Uterus, while the Chong Mai delivers Blood to the Uterus. The Uterus Channel (also known as the Bao Mai channel) provides a direct connection to the Kidneys; Kidney Essence, as mentioned above, is the primary source of Tian Gui, or menstrual blood. 

The health of the Uterus is, of course, essential for getting pregnant and maintaining a healthy pregnancy. It is responsible for storing and releasing menstrual blood, thickening the endometrial tissues, holding the fetus during pregnancy, receiving sperm, managing the process of ovulation each month, and storing Kidney Essence (Jing). In addition to having a close connection with the Kidneys, the Uterus is also connected intimately with the Heart and the Liver. The Liver Qi directly stimulates the movement of menstrual blood, while the Heart is also connected to the Uterus via the Bao Mai Channel. The Heart-Uterus connection is seen through the way that emotions and thoughts can directly affect a woman’s menstrual cycle or reproductive organ health.

The Stomach and the Uterus intersect peripherally, since both connect to the Chong Mai Channel, and the Spleen has a more indirect connection to the Uterus through its responsibilities in blood production. 

Common Kidney Disorders During Pregnancy

Hydronephrosis is one of the most common kidney-related issues seen during pregnancy, and occurs when the kidneys stretch and swell excessively in response to the buildup of urine. Conditions affecting the right ureter of the kidneys are also more common, due to the angle at which this ureter crosses the iliac and the ovarian vessels at the entry into the pelvis. 

There are 3 categories of serious kidney injuries: prerenal, intrinsic renal, and postrenal. Prerenal conditions are caused by decreased renal perfusion (blood flow), which is generally due to decreased blood volume. Intrinsic renal conditions are caused directly by a process within the kidneys. Finally, postrenal conditions are caused by inadequate drainage of urine into the bladder from the kidneys. During pregnancy, kidney injury can be lead to the following health problems: 

• Hyperemesis gravidarum (prerenal)
• Bleeding during later stages of pregnancy (prerenal)
• Acute fatty liver of pregnancy / AFLP (prerenal and/or intrinsic renal)
• Postpartum bleeding (prerenal)
• Higher risk of side effects from medications (prerenal)
• Progression of chronic kidney disease / CKD (intrinsic renal)
• Glomerulonephritis / Postinfectious glomerulonephritis (intrinsic renal)
• Complications resulting from hemorrhage, sepsis, UTI’s, and kidney stones (intrinsic renal)
• Familial hemolytic uremic syndrome / HUS (intrinsic renal)
• Thrombotic thrombocytopenic purpura / TTP (intrinsic renal)
• Anticardiolipin antibody syndrome (intrinsic renal)
• Severe preeclampsia / HELLP (intrinsic renal)
• Pyelonephritis (intrinsic renal)
• Acute tubular necrosis / ATN from sepsis or hemorrhage (intrinsic renal)
• Obstruction from kidney stones or in the uterus (postrenal)
• Retained blood clots during postpartum (postrenal)

UPDATE 2024: Note that recently, scientists have discovered a link between kidney-related health problems during pregnancy and postpartum depression. If you've been diagnosed with a health issue related to the kidneys during pregnancy (this includes gestational diabetes, pre-eclampsia and eclampsia, kidney infection, urinary tract infection, kidney stones, and any of the diseases in the list above), be sure to click here and read this article to learn more about how to take special care of your kidneys after you give birth to prevent postpartum depression.

Click here to download "The Natural Women's Health Guide... To Pregnancy: Nutrition and Supplements to Prevent and Treat Pregnancy-Related Conditions".

Click here to subscribe to the Living Database!

Resources: