When Your Body Works For Two: How To Prepare It Before Pregnancy, Part 1

Pregnancy is a period when the body begins to function under significantly altered conditions. Within a short time, the systems of circulation, digestion, hormonal regulation, immunity, metabolism, and the functioning of internal organs undergo restructuring. These changes are normal and are aimed at the development of the child; however, they require a large amount of resources and stability of all physiological processes.

During pregnancy, any hidden or barely noticeable disturbances become more pronounced. Deficiencies of iron, vitamin D, B12, or iodine, unstable thyroid function, a tendency toward fluctuations in blood sugar, episodic digestive problems, periodic urogenital infections, occasional inflammatory processes, or fatigue - everything that previously manifested as a moderate increase in heart rate and was perceived as “normal” and easily compensated - is felt more strongly during pregnancy. The body operates under increased load and with a smaller margin of safety, which makes it harder to compensate even mild deviations.

At the same time, the possibilities for intervention during this period are very limited. Many treatment and diagnostic methods become undesirable or impossible, and active correction protocols that are easily implemented before conception require caution during pregnancy or are simply prohibited. What could be quickly corrected before now has to be managed with gentler measures or merely monitored in order not to harm the fetus.

For this reason, preparation for pregnancy is of critical importance: it makes it possible to stabilize bodily function in advance, correct deficiencies, reduce the load on key systems, improve tolerance of pregnancy, and create conditions for the full development of the child from the very first weeks.

Physiological Changes During Pregnancy

Understanding the general principles of adaptation is important, but in order to see which mechanisms underlie changes in well-being during pregnancy, they need to be considered by systems. Pregnancy does not create strain in a single area - it initiates sequential and interconnected changes in the function of the heart, kidneys, liver, immune regulation, hormones, and metabolic processes. Different systems adapt at different times, which is why well-being may change in stages.

To understand which processes, have the greatest impact on well-being and why advance preparation is so important, the following sections examine in detail the main physiological adaptations of pregnancy and their effects on the body of the expectant mother.

Cardiovascular Load

During pregnancy, the volume of circulating blood increases by nearly half in order to supply the placenta and the fetus. The heart pumps a larger volume of blood: blood volume increases by 30-50%, heart rate rises, and the load on the cardiovascular system increases significantly.

In early pregnancy, under the influence of progesterone and placental factors, blood vessels become softer and wider, vascular resistance decreases, and blood pressure temporarily drops in many women. This explains the frequent dizziness when standing up - a consequence of vascular adaptation to new conditions.

As the placenta grows and blood volume increases, factors that were latent before pregnancy begin to manifest: low ferritin or hemoglobin, moderately increased heart rate, vitamin D deficiency, subtle thyroid dysfunction, low physical conditioning, or valvular characteristics. What was previously compensated becomes noticeable: fatigue, palpitations, shortness of breath, and reduced exercise tolerance appear.

A decrease in hemoglobin increases the load on the heart. With a reduced ability of the blood to carry oxygen, the body compensates by increasing heart rate, which is why even a moderate reduction in ferritin or hemoglobin becomes noticeable as early as the first trimester.

The placenta also regulates vascular tone and blood flow, influencing vascular responses. Baseline vascular health, stress levels, sleep quality, and physical activity determine how smoothly adaptation occurs.

Thus, cardiovascular load during pregnancy is a natural process that requires substantial reserves. The better the iron status, thyroid function, vascular condition, and overall level of physical fitness before pregnancy, the easier the adaptation and the lower the risk of pronounced symptoms.

Renal Load

During pregnancy, the load on the kidneys increases from the very first weeks. As circulating blood volume rises, the rate of renal filtration increases by approximately 50%, and the kidneys must excrete metabolic waste products from both the mother and the fetus. This adaptation requires sufficient reserves of the excretory system.

Progesterone reduces the tone of the smooth muscles of the urinary tract: the ureters dilate, urine flow slows, creating conditions for urinary stasis - a key risk factor for bacterial growth. Therefore, even in the absence of pathology, the likelihood of urogenital infections is higher during pregnancy.

In the third trimester, mechanical pressure from the enlarged uterus on the bladder is added, impairing bladder emptying. Residual urine forms a favorable environment for bacterial proliferation, and the risk of infections increases.

In women with healthy kidneys, these changes are usually well compensated. However, if there were pre-existing vulnerabilities before pregnancy - asymptomatic bacteriuria, a tendency toward cystitis, low hydration, small crystals in the urinary tract, or metabolic features predisposing to stone formation - they become more pronounced precisely under the increased load of pregnancy.

Thus, renal load during pregnancy is a combination of hormonal and mechanical factors that increase the sensitivity of the system to existing disturbances. Good baseline health of the excretory system before conception and its monitoring during pregnancy reduce the risk of complications.

Hepatic Load

During pregnancy, the liver experiences one of the highest metabolic loads. Concentrations of estrogens and progesterone increase dozens of times, and it is the liver that processes their metabolites while simultaneously maintaining glucose levels, lipid metabolism, and the function of detoxification and elimination systems. Already in the first weeks, enzyme activity changes, and the metabolism of substances becomes different.

The hormonal background also affects the function of these systems: in some women, the balance of enzymatic processes shifts, which can increase the circulation of intermediate metabolic products and intensify sensitivity to odors, fatigue, and sensitivity to certain foods - especially in the presence of deficiencies in B-group vitamins, magnesium, or amino acids.

Estrogens and progesterone slow bile outflow: the gallbladder contracts less effectively, and bile movement becomes slower. This is physiological, but if there was already a tendency toward bile stasis or discomfort after fatty foods before pregnancy, symptoms become more pronounced due to the increased load on the biliary pathways.

Additional load is created by the utilization of fat stores. Along with fat, substances accumulated in adipose tissue may be released into the bloodstream. The liver processes them simultaneously with a large volume of hormonal metabolites, which particularly increases the load in early pregnancy.

The placenta also influences hepatic metabolism by regulating lipid levels, hormonal balance, and vascular responses. Therefore, any baseline features - reduced bile flow activity, elevated triglycerides, disturbances in microbiota balance - become more noticeable during pregnancy.

Immune System

During pregnancy, the immune system shifts into a mode of reduced immune reactivity in order to protect the fetus from excessive immune responses while maintaining the ability to resist external infections. Immunity does not “switch off,” but the balance of different components changes: some responses become milder and slower, while mechanisms related to tissue tolerance become more active.

This makes the body more vulnerable to bacterial and fungal infections, especially at mucosal surfaces. The speed of immune response decreases, protective function becomes less effective, and even minor local inflammatory processes - in the respiratory tract, intestines, skin, or urinary tract - may occur more frequently and persist longer. A predisposition to microbiota imbalance, skin inflammation, or episodic infections that was hardly noticeable before pregnancy becomes more evident precisely because of the naturally weakened immune response.

The hormonal background reinforces this dynamic: progesterone reduces the activity of certain immune cells and makes mucous membranes more susceptible to pathogens, while high estrogen levels alter the function of immune system receptors. These changes are expected and reversible, but under increased physiological load they require a resilient immune system even before conception.

Interestingly, against the background of a milder response to infections, many autoimmune diseases temporarily decrease in symptom severity. This reflects reduced activity of cells capable of attacking the body’s own tissues. After childbirth, the immune system returns to its previous level of activity, and autoimmune processes may intensify again.

Thus, immune adaptation during pregnancy is not suppression but reconfiguration. It is necessary to protect the fetus, but it makes the body less resistant to external infections and latent inflammatory factors. Therefore, correction of chronic inflammation, restoration of the microbiota, and treatment of recurrent infections are best carried out before pregnancy, when the immune system operates in its usual mode.

Hormonal Restructuring

Estrogen prepares the endometrium for pregnancy by supporting its growth and the development of receptors. After ovulation, progesterone shifts the endometrium into a state that supports implantation and becomes the main hormone responsible for maintaining early pregnancy. If progesterone levels are insufficient, the risk of early miscarriage increases significantly, despite normal estrogen-mediated preparation of the uterus.

Progesterone also reduces smooth muscle tone and affects the nervous system. It causes drowsiness, changes in energy levels, and an increased need for rest - characteristic features of early pregnancy. These mechanisms are not considered a source of gastrointestinal or urological symptoms, as these aspects are discussed in detail in the relevant sections.

Estrogens influence vascular tone: the vascular wall becomes more elastic and relaxed, which reduces peripheral resistance and explains lower blood pressure in early pregnancy. Later, as blood volume increases by almost 40-50%, the vascular system adapts again, and blood pressure may return to baseline or increase - especially in the presence of a tendency toward vascular instability or magnesium deficiency.

The thyroid gland increases its activity by 30-50% in early pregnancy, since thyroid hormones are essential for fetal nervous system development and for maintaining maternal metabolism. The requirement for iodine increases markedly. Even a mild deficiency may affect energy levels, cognitive function, and early fetal development; therefore, thyroid status before conception and in the first trimester is of key importance.

Pregnancy hormones also alter the regulation of metabolism. In the second half of pregnancy, a physiological reduction in insulin sensitivity develops - an adaptation that ensures preferential glucose delivery to the fetus. The detailed mechanisms and clinical implications of this process are addressed in the section on metabolic load.

Hormonal fluctuations also affect emotional regulation: neurotransmission, stress sensitivity, and sleep cycles change. These changes are part of normal adaptation and depend on the stability of the endocrine system before pregnancy.

Anemia and the Demand for Hematopoiesis

During pregnancy, the body needs to produce a significantly larger blood volume. The placenta, the uterine vascular network, and the growing fetus require a constant supply of oxygen and nutrients, which leads to a marked increase in circulating blood volume. This requires active production of red blood cells, which is impossible without adequate amounts of iron, folic acid, and vitamin B12.

At the same time, the requirement for iron increases approximately three- to fourfold. A normal hemoglobin level before pregnancy does not guarantee stability, because the decisive factor is iron stores - the ferritin level. If these reserves were low or borderline, they are rapidly depleted already in the first trimester, when the additional blood volume is being formed and a significant portion of iron is directed to the fetus. Therefore, women with normal hemoglobin but low ferritin more often encounter iron deficiency during pregnancy.

The fetus is fully dependent on the mother’s iron, folic acid, and vitamin B12. Its needs are prioritized. If maternal stores are insufficient, symptoms are experienced by the woman: shortness of breath, increased heart rate, reduced endurance, dizziness, and weakness.

A decrease in blood oxygen levels leads to an increased heart rate and, consequently, to an increased cardiac load. This is why even mild iron deficiency affects exercise tolerance, the sensation of air hunger, and overall energy levels.

Folic acid and vitamin B12 are essential for the division of blood cells and for the development of the fetal nervous system. Their deficiency affects not only hemoglobin levels but also neural tube development and the mother’s metabolic state. In the absence of sufficient B12, folic acid cannot fully carry out its functions, which is why these nutrients are always assessed together. Deficiencies that were previously unnoticed become clinically apparent under conditions of increased demand.

Iron deficiency also affects the child’s condition. Low iron stores at birth are associated with risks of delayed nervous system and cognitive development, sleep disturbances, increased irritability, and reduced adaptation to external stimuli. The fetus builds its own iron stores toward the end of pregnancy, which makes maternal iron status particularly important in the third trimester. At the same time, correction must begin in advance, since increasing ferritin levels requires time.

All of these adaptations are physiological but require substantial reserves. Iron, folic acid, and vitamin B12 status before pregnancy largely determines tolerance of the increasing blood volume and the ability to supply oxygen to the developing child. Bringing these parameters into optimal range before conception is one of the key elements of preparation for a healthy pregnancy.

Gastrointestinal Tract and Digestion

The digestive system is among the first to respond to pregnancy. Progesterone relaxes smooth muscle, intestinal motility slows, and food moves more slowly through the gastrointestinal tract. This creates the typical picture of early pregnancy: a tendency toward constipation, heaviness after meals, bloating, and a more pronounced reaction to meal volume.

Relaxation of the sphincter between the esophagus and the stomach increases the likelihood of acid reflux. Heartburn often appears already in the first trimester and becomes more pronounced as the fetus grows and intra-abdominal pressure increases. Even familiar foods can cause discomfort, and the sensation of fullness occurs more quickly.

Bile function also affects digestion, but in this section the focus is on clinical manifestations. Slower bile flow worsens fat digestion and becomes one of the factors contributing to early toxicosis: nausea intensifies, intolerance to fatty foods develops, sensitivity to odors increases, and morning vomiting may occur. Here bile is considered as part of gastrointestinal symptomatology rather than as a description of hepatic metabolic processes.

Changes in gastric motility and acidity affect nutrient absorption. Iron, vitamin B12, amino acids, and some minerals are absorbed less efficiently under conditions of reduced acidity or delayed gastric emptying. This explains why minor deficiencies that were previously unnoticed quickly become clinically significant: the risk of iron deficiency increases not only because of the expanding blood volume but also due to physiological changes in digestion.

The intestinal microbiota also undergoes adaptation. Slower transit, changes in bile composition, and hormonal influences alter conditions within the intestinal lumen: some bacterial groups become more active, while others become less prominent. This affects immune balance, inflammatory sensitivity, and overall well-being. If there were pre-existing signs of microbiota imbalance before pregnancy (unstable stool, bloating, food reactivity), they often become more pronounced.

All of these changes are physiological but require stable gastrointestinal function. Stabilizing digestion before conception - reducing heartburn, normalizing bowel movements, maintaining adequate gastric acidity, improving fat tolerance, and restoring the microbiota - significantly reduces the likelihood of toxicosis and the severity of digestive symptoms in the first trimester.

Metabolic Load and Reduced Insulin Sensitivity

Metabolic load during pregnancy increases gradually. The body must supply energy to its own tissues and to the growing fetus, for whom glucose is the primary source of fuel. To ensure a stable supply of glucose to the fetus, maternal tissue sensitivity to insulin is physiologically reduced. This mechanism is initiated by placental hormones and reaches its peak in the second half of pregnancy.

Under the influence of placental lactogen, estrogens, progesterone, and cortisol, cells become less sensitive to insulin. The pancreas compensates by producing more of the hormone. In women with stable pancreatic beta-cell function, blood glucose levels remain normal. However, in the presence of reduced reserve capacity - due to genetic predisposition, excess weight, low physical activity, magnesium or vitamin D deficiency, or chronic stress - insulin resistance becomes more pronounced, increasing the risk of gestational diabetes.

Changes in glucose metabolism affect other systems as well. Even moderate elevations in blood glucose increase inflammatory background, raise the burden on cellular repair processes, affect blood vessels, and impair nutrient utilization. This can exacerbate fatigue and reduce tolerance to physical activity. Glucose in the urine creates favorable conditions for bacterial growth, which partly explains the higher frequency of urinary tract infections when glucose tolerance is impaired.

Lipid metabolism also undergoes adaptation. Early in pregnancy, lipid levels may be lower than usual, but later cholesterol and triglycerides increase predictably - this is necessary for placental development, hormone synthesis, and fetal cell membrane formation. In the presence of pre-existing lipid metabolism disturbances, these changes may be more pronounced and require monitoring.

These adaptations require substantial resources. If blood glucose levels were unstable before pregnancy, insulin sensitivity was already reduced, or excess body weight was present, the load on the pancreas increases more rapidly, raising the likelihood of gestational diabetes and related complications, including excessive fetal growth.

Therefore, optimal metabolic status before conception - stable blood glucose, good insulin sensitivity, regular physical activity, and balanced nutrition - plays a key role in how well the body tolerates the metabolic demands of pregnancy.

Musculoskeletal Load

During pregnancy, the body gradually changes movement patterns and posture. As the fetus grows, the center of gravity shifts forward, and familiar movements require greater effort. This increases the load on the muscles of the back, pelvis, and legs, even if the woman did not previously experience discomfort. Simple activities - prolonged standing, walking, getting out of bed - may feel different specifically due to altered load distribution.

Under the influence of relaxing, ligaments become softer and more mobile. This is important for preparation for childbirth, but it affects not only the pelvic region - stability of the knees, ankles, spine, and small joints also changes. This increased mobility makes muscles and joints more sensitive to load, especially if deep core muscles were insufficiently strong before pregnancy. A woman may notice that familiar loads, bending, or long walks require more energy and lead to rapid fatigue.

Postural changes increase strain in the lumbar region. Back muscles work more intensively to compensate for the shifted center of gravity, which explains frequent pain, a sensation of heaviness, and fatigue in the lower back. Even mild pre-pregnancy features - weak muscular support, flat feet, minor postural deviations, or old injuries - become more apparent because the load increases with each month.

Pregnancy also affects venous return. The growing uterus exerts pressure in the pelvic area and slows blood outflow from the legs. Combined with hormonally induced relaxation of the vascular wall, this can lead to varicose veins, edema, and a feeling of heaviness in the legs. In women with impaired venous outflow, symptoms are more pronounced.

Overall muscular and joint load is also influenced by systemic factors: reduced energy due to anemia, gait changes from the enlarging abdomen, possible sleep disturbances, and fluctuations in physical activity. All of this increases the body’s need for a resilient musculoskeletal system. If the abdominal, back, pelvic floor, or leg muscles were weak before pregnancy, the load increases faster and discomfort develops earlier.

Maintaining muscle tone before pregnancy - especially in the deep abdominal, back, and pelvic floor muscles - significantly improves tolerance of pregnancy. Moderate physical activity, good hydration, weight management, and postural work help reduce the risk of pain, edema, varicosities, and increased fatigue. The more resilient the musculoskeletal system, the more easily it adapts to the increasing load of each trimester.

Conclusion

Pregnancy involves a sequential and interconnected adaptation of all major physiological systems. As it progresses, the dominant load shifts from hormonal and vascular mechanisms to metabolic, hematologic, and mechanical factors, which is why even previously subtle deficiencies or functional vulnerabilities may become clinically apparent. At the same time, options for active correction during pregnancy are limited, making prevention and stabilization before conception especially important.

Preparation for pregnancy helps build the necessary physiological reserve by stabilizing iron and vitamin status, supporting thyroid function, metabolism, gastrointestinal health, and cardiovascular and musculoskeletal resilience. The more stable the body’s baseline condition, the easier pregnancy is to tolerate, the lower the risk of complications, and the more favorable the conditions for the child’s development from the earliest weeks.