The Bottom Line

Women experience numerous and diverse physiological changes to support a growing pregnancy, which begin almost immediately.

Hormones are largely responsible for almost all these changes. As the early embryo implants, it releases human chorionic gonadtropin (HCG) into the blood stream. The corpus luteum then starts to release progesterone and relaxin, and a host of changes start happening within the body – affecting nearly every organ.

Although many aspects of these changes are obvious (i.e. enlarging uterus), there is a lot the medical community still does not understand regarding how the body adapts and changes during pregnancy (i.e. the immune system).

Further, studying and characterizing these changes, to include each specific organ, is difficult to do during a pregnancy.  Researchers are extremely limited in certain methods, imaging scans, and measurement techniques to collect more data/information.

Regardless, it is clear that the normal and necessary physical changes of pregnancy generate many symptoms and conditions that pregnant women have accepted as just a part of pregnancy itself.

But if women better understand their bodies, its anatomy, how and why hormones affect certain organ systems, and how they may be able to anticipate and prepare for some of these symptoms (if they occur), women can enjoy a happier, safer, more comfortable, and less anxious pregnancy – and feel more in control of their own health.

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Hormones are largely responsible for almost every physiological change during pregnancy. Because women respond differently to hormones, not every woman will experience the same changes or resulting symptoms. Some women may only experience a few bothersome symptoms, while others may experience an avalanche of uncomfortable effects.

Hormones are released directly into the bloodstream by endocrine glands within the body such as the pituitary gland, adrenal glands, ovaries, and thyroid gland. One of the most powerful, temporary endocrine glands in all of human health is the placenta.

The reproductive hormones include human chorionic gonadtropin, progesterone, prolactin, relaxin, placental lactogen, and various estrogens (as well as others). These hormones are all released during pregnancy to ensure successful implantation and healthy fetal growth and development.

Hormones work by docking to receptors located within a specific location of the body. For example, the uterus has receptors for oxytocin; at term, the pituitary gland releases oxytocin which binds to its receptors in the uterus, which communicates to the uterus to make a change – to contract (the uterus also gains more receptors at term).

Since these hormones collectively have receptors in almost all organs of the body, they cause a seemingly endless list of physical, mental, and emotional alterations to the body that continuously change as pregnancy progresses.

Photo by Mustafa Omar on Unsplash

An understanding of these changes and how they lead to various symptoms helps HCPs determine the management for these symptoms, if they put women at risk for certain complications, or whether a certain symptom may, instead, be a sign of an unrelated health problem.

Content Summary

Note: Not all women will experience the changes described below and some women will experience greater change than others. They are all presented together so women understand how hormones can affect the entire body.

Abdominal muscles: The strength and function of the abdominal muscles play significant roles in protecting the core’s ability to adapt with pregnancy while preventing back and pelvic pain. Separation of these muscles is very common during pregnancy (diastasis recti), which can take a few weeks to a few months to return to its pre-pregnancy state. Read more.

Resulting symptoms/conditions: Back pain; Pelvic pain; Instability

Back and Spine: Adjustments of the curvature of the spine during pregnancy are debated. However, regardless of whether this curvature changes, the back and spine experience enormous physical stress during pregnancy due to extra body weight, larger breasts, a growing uterus, and a change in gait and walking pattern, as well as a shift in a woman's center of gravity. This stress can cause joint, muscle, and bone pain in the upper and lower back. Read more.

Resulting symptoms/conditions: Back pain; Pelvic pain; Instability; Insomnia; Fatigue

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Bladder and Pelvic Floor: Bladder, ureter, and urethra tone all decrease and weaken during pregnancy, the bladder is displaced and holds less urine in late pregnancy, and the uterus adds significant weight and pressure. Read more.

Related symptoms/conditions: Various Urinary Symptoms such as frequency, trouble voiding, leakage; Urinary Tract Infections; Prolapse

Blood Volume: Blood volume increases almost 50% during pregnancy, beginning in the first trimester, which involves mostly an increase in plasma.  Proper blood volume increase ensures healthy fetal and placental growth and development as well as adequate protection against blood loss during delivery. However, this extra volume is responsible for many different symptoms and specific risk factors during pregnancy. Read more.

Brain: Research into pregnancy-related brain changes is still very new, but researchers have started to identify some physical changes within the brain that may be an adaptation for motherhood.  Evidence is conflicted, however, on whether “pregnancy brain” is due to specific brain-related changes, or if this commonly reported symptom is the result of other symptoms, such as fatigue, lack of sleep, and a split-focus (delivery, new baby, etc.). Read more.

Related symptoms/conditions: Memory Loss

Note: Headaches are currently not assessed to be related to brain changes during pregnancy, but likely due to blood volume changes and other adaptations.

Breasts: Largely under the influence of estrogen, rapid and significant breast changes occur in the first half of pregnancy that can cause them to enlarge very quickly.  Milk production also starts early (colostrum), then peaks in speed during the last few weeks of pregnancy.  These physical changes in a short amount of time can produce potential concerns of new lumps in the breasts, the vast majority of which are benign. Read more.

Related symptoms/conditions: Breast Tenderness, Breast Lumps, Back Pain

Cervix: The cervix undergoes remarkable changes during pregnancy, from changing in color, to strengthening and lengthening to maintain a pregnancy, only to reverse and soften, thin, and dilate at term. The cervix also has the ability to remodel once again to allow for additional pregnancies. The cervix’s inability to either strengthen, or efface and dilate during pregnancy, or return back to normal can lead to complications. Read more.

Related symptoms/conditions: Insufficient Cervix, Preterm Labor, Mucus Plug, Rupture of Membranes

Ear, Nose, and Throat: Pregnancy affects almost every aspect of the ear, nose, and throat – due to blood volume changes that can cause fluid buildup in the ear and nasal membranes/blood vessels.  The throat is indirectly affected as a result of these and other changes in the body that lead to mouth breathing, post-nasal drip, snoring, and acid reflux. Read more.

Related symptoms/conditions: Nasal Congestion, Ear Congestion, Dizziness, Aversions

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Gall Bladder Liver and Pancreas: Changes to the liver, gallbladder, and pancreas are mostly caused by the increase in progesterone, which may cause organ motility to slow down – the same effect that is also theorized to occur in the stomach. Due to slower movement of the gallbladder, bile salts can back up and affect all three organs, leading to various symptoms. The pancreas can also have trouble with the increased amount of insulin required during pregnancy, leading to gestational diabetes. Read more.

Gastrointestinal (GI) Tract: The GI tract is largely affected due to progesterone’s relaxation effect on organ motility, which causes food to stay in the GI tract longer, leading to various symptoms. However, this is debated, and researchers do not yet know the full hormonal effects on the GI tract, whether motility is affected at all, and if it is, to what degree and whether those changes are the cause of certain symptoms.  Read more.

Hair and Nails: The hair cycle is altered during pregnancy, and women will likely feel thicker and fuller hair due to a larger amount of hairs remaining in the scalp. Hair strands can also grow faster and increase in diameter. True additional hair growth can also occur on other parts of the body (face, abdomen, back), but is usually temporary. Read more.

Resulting symptoms/conditions: Hair Loss, Chipped Nails, Extra Hair Growth (all in Hair and Nails)

Hands and Feet: Relaxin, along with increased fluid volume, are responsible for most physical changes and symptoms related to the hands and feet. The hands can itch, swell, and potentially turn red in color due to blood vessel changes in the hands, while the wrists can experience nerve pain due to the constriction. Feet can swell and feel sore due to increased weight, increased fluid, and a change in walking pattern during pregnancy. Read more.

Resulting symptoms/conditions: Itchiness, Swelling, Carpel Tunnel, Increased Foot Size (all in Hands and Feet page)

Heart: The cardiovascular system is the first major organ system to change during pregnancy and is one of the most important in ensuring the success of the health of both mother and baby. Blood volume, flow, pressure, heart rate, and cardiac output all change almost immediately. Read more.

Hormones: Hormones ensure successful ovulation, fertilization and implantation, fetal growth and development, the initiation of labor, detachment of the placenta, and the production of colostrum and breastmilk. Researchers are still learning exactly which hormones have which roles during pregnancy, what levels are normal, and how to use hormones to prevent or treat pregnancy-related complications. Read more.

Related symptoms/conditions: Since hormones are the major agents that initiate physical changes during pregnancy, hormonal changes are responsible for almost all symptoms.

Immune System: The latest research indicates a pregnant woman’s immune system is not suppressed – it adapts to the pregnancy, allows it to thrive, and does not make a pregnant woman more susceptible to contracting an infection. However, the adapted immune system, together with lung, heart, and blood volume changes during pregnancy, can make it harder for women to fight off infections (listeria, influenza, etc.) and complications after becoming ill.  Read more.

Resulting symptoms/conditions: Depending on each individual woman and her health prior to pregnancy, immune system changes can make some pre-existing conditions worse, while making others much better during pregnancy.

Kidneys: Kidneys do a lot of work during pregnancy. Under the influence of hormones, kidneys increase urine production, eliminate waste at a faster rate, and regulate the crucial balance between sodium and fluid. While this process is not well understood during pregnancy, it is clear that keeping kidneys healthy can ease urinary symptoms and prevent numerous potential complications. Read more.

Resulting symptoms/conditions: Increased urination; Increased nutrient clearance; Proteinuria; kidney stones

Photo by Michael Anfang on Unsplash

Musculoskeletal System: Connective tissues of the body loosen and stretch (relaxin) to accommodate the growing uterus, and to allow the baby to pass through the bones of the pelvis during vaginal delivery. This loosening, while necessary, causes loosening and stretching of most other connective tissues – including the ribs – and can cause other issues such as back, pelvic, and joint and ligament pain, along with a risk of potential injury. Read more.

Ovaries: Correct function of the ovaries (through hormones) regulates the menstrual cycle and allows for ovulation and successful implantation through the development and survival of the corpus luteum. Read more.

Resulting symptoms/conditions: Bleeding (spotting)

Respiratory System: Pregnancy causes unique changes to the respiratory system due to an increase in oxygen requirements; the rib cage spreads up and out, the diaphragm is pushed up, muscle strength is reduced, and women can feel out of breath from normal everyday activities (progesterone and relaxin). Read more.

Resulting symptoms/conditions: Hyperventilation; Shortness of Breath; Fatigue

Skin: Skin changes affect up to 90% to 100% of all pregnant women and are caused mostly by hormonal influences on skin cells, blood vessels, and the immune system and liver (which can indirectly affect the skin). Read more.

Resulting symptoms/conditions: Rashes; Stretch Marks; Itching; Discoloration (all in Skin); Acne; Varicose Veins; Intrahepatic Cholestasis of Pregnancy; Polymorphic Eruption of Pregnancy

Teeth and Gums: Hormones cause changes to the gingiva (gums) and saliva during pregnancy that can negatively affect the health of the entire mouth, even with good oral hygiene. Read more.

Resulting symptoms/conditions: Gingivitis, Excess Saliva, Periodontal Disease, Loose Teeth, Cavities (all in Teeth and Gums)

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Uterus: The uterus changes in size, weight, volume, and blood flow in order to support, develop, and protect a pregnancy. Researchers are still learning about the how the uterus performs these functions, to include its response to labor hormones and contractions.  The largest affect the uterus has on a pregnant woman is its stretching, which causes discomfort in moving, sitting, sleeping, and even breathing. Read more.

Vagina: Like the cervix, the vagina undergoes remodeling of its tissues to support stretching of its walls during delivery and a return to normal in the postpartum period (as much as possible). However, hormones can also affect the vagina's microbiome, which makes it more susceptible to infection. Read more.

Resulting symptoms/conditions: Infection, Swelling, Discharge (all in Vagina)


Which reproductive hormones have receptors in which organs?

Can the rise and fall of certain hormone levels be directly linked to the average onset and relief of specific symptoms? (For example, relaxin and HCG are debated in this regard for joint/muscle pain, and nausea/vomiting respectively.)


On each individual page above, where applicable, are Partner/Support sections where a pregnant woman's partner, or anyone who supports her, can learn how to assist her and provide her some relief with these physical changes of pregnancy.

Women do not have to go through these changes alone; there are small steps and actions partners/loved ones can take to improve their symptoms, pain, and discomfort, and overall, help her have a much easier pregnancy.

Partners, along with pregnant women, should also learn warning signs or other possible indications related to these changes to understand when it may be time to call an HCP.


How Hormones Work (BC Campus OpenText; Anatomy and Physiology)

Types of Hormones (Tulane University)

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