When Your Body Works For Two: How To Prepare It Before Pregnancy, Part 2

Although the physiological changes of pregnancy develop simultaneously across many systems, different processes may dominate at different stages. In early pregnancy, hormonal shifts, restructuring of vascular tone, activation of the thyroid gland, and increased toxic load associated with the processing of a large volume of hormonal metabolites are more pronounced. In mid-pregnancy, the increasing metabolic load and the expansion of circulating blood volume come to the forefront. In late pregnancy, mechanical and compressive factors related to uterine growth become more prominent.

These are not separate stages, but a gradual shift of emphasis, in which some mechanisms become leading while others continue to function in the background. It is precisely this sequence that makes even minor pre-existing disturbances significant, because the load shifts from one system to another as pregnancy progresses.

First Trimester: Increase in Sex Hormones, Thyroid Load, Decrease in Blood Pressure and Immune Protection, and Early Changes in Detoxification Systems

The first trimester is the period of the most abrupt and rapid restructuring of the body. Levels of progesterone and estrogens rise manyfold from the very first weeks, and the thyroid gland is forced to work 30-50% more actively to ensure normal development of the fetal nervous system. Even a mild pre-existing deficiency of thyroid hormones during this period can affect maternal well-being and early fetal nervous system development, causing irreversible changes in the child’s brain if these hormones are insufficient. Therefore, thyroid status is one of the key factors specifically in the first trimester.

The vascular system responds in parallel. Under the influence of hormones, blood vessels dilate, peripheral resistance decreases, and blood pressure in many women drops below their usual levels. This explains dizziness, weakness when rising, and light-headedness upon standing. These changes are physiological, but they exacerbate any underlying vascular issues, anemia, dehydration, or electrolyte deficiencies.

The liver must process a sharply increased volume of hormones, and this coincides with a physiological slowing of bile flow and gastrointestinal motility. As a result, nausea intensifies, tolerance to fatty foods decreases, and sensitivity to odors increases. If fat-soluble toxins have accumulated in the body - pesticides, heavy metals, lipophilic metabolites - their mobilization from adipose tissue during this period can place an additional burden on detoxification systems, making symptoms more pronounced.

The body actively consumes folate and vitamin B12. These nutrients are essential for early tissue development and closure of the neural tube. Even minor insufficiencies that were not noticeable before pregnancy become significant already in the first weeks. Iron stores also begin to be utilized, but in the first trimester the key factors are adequate folate and B12 levels.

The immune system shifts into a state of reduced immune reactivity. Protective responses become milder, and susceptibility to viral infections, candidiasis, and urogenital infections increases. Inflammatory processes that were previously hidden or fully compensated often become apparent. This is the period when identified infections need to be treated even in the presence of minimal symptoms, because at this stage the immune system is not able to rapidly resolve the problem on its own.

Second Trimester: Peak Blood Volume, Increased Load on the Heart, Kidneys, and Liver, and Progressive Reduction in Insulin Sensitivity

By mid-pregnancy, the body gradually enters a state of relative stability, while at the same time carrying one of the most significant loads - an increase in circulating blood volume. The heart must work more intensively, heart rate increases, and the volume of blood pumped by the heart becomes substantially higher. Against this background of expanding blood volume, arterial blood pressure in many women returns to pre-pregnancy levels after the physiological decrease observed in the first trimester. However, in some women, a tendency toward elevated blood pressure appears precisely in the second trimester, especially if there were pre-pregnancy signs of increased vascular sensitivity to stress, magnesium deficiency, or episodes of stress affecting the regulation of vascular tone.

In women with low ferritin, vitamin D deficiency, or reduced thyroid function, symptoms of cardiovascular strain may become more noticeable: pronounced fatigue, shortness of breath, increased heart rate, and reduced tolerance to physical activity appear.

The kidneys filter a significantly larger volume of fluid. Renal filtration increases by approximately half, and small amounts of glucose may appear in the urine, creating a favorable environment for bacterial growth. If there was a predisposition to cystitis before pregnancy, such episodes tend to recur more frequently in the second trimester - and, unlike in the first trimester, they are usually accompanied by more clearly expressed symptoms.

During this period, the liver processes the maximum amount of hormones. If there were pre-pregnancy signs of slowed bile flow, intolerance to fatty foods, or dysbiosis, symptoms may become more pronounced due to the increased load on the gallbladder and detoxification pathways. It is the hormonal background that often leads to the appearance of acid reflux in the second trimester.

In the second half of the trimester, the physiological reduction in insulin sensitivity begins to intensify. This is a normal mechanism that ensures a stable supply of glucose to the fetus. In women with sufficient compensatory capacity, blood glucose levels remain stable. However, if the pancreas is already operating near its limit - due to genetic predisposition, excess body weight, low physical activity, stress, or vitamin D deficiency - glucose levels begin to rise more quickly, and the risk of gestational diabetes increases. Elevated glucose affects overall well-being, increases fatigue, and raises the risk of urinary tract infections, since glucose appears more frequently in the urine.

It is precisely in the second trimester that magnesium levels begin to decline in a substantial proportion of women. This manifests as muscle cramps, increased irritability, and sleep disturbances, and may affect vascular regulation, increasing the tendency toward blood pressure fluctuations. With significant magnesium deficiency, the risk of impaired uterine contractility and adverse pregnancy outcomes increases, including the risk of miscarriage.

Third Trimester: Mechanical Pressure of the Uterus on Organs, Pronounced Metabolic Load, and Peak Demands on the Heart, Kidneys, and Musculoskeletal System

In the final phase of pregnancy, the load becomes predominantly mechanical and metabolic. Circulating blood volume reaches its maximum, the heart works significantly more intensively, and many women experience shortness of breath, palpitations, and rapid fatigue.

The growing uterus exerts pressure on the bladder, interferes with complete emptying, and increases the risk of urinary tract infections. Even moderate elevations in blood glucose further increase this risk, since glucose in the urine serves as a nutrient medium for bacteria.

The liver continues to process large volumes of hormones. If there were pre-pregnancy signs of impaired bile outflow or intolerance to fatty foods, symptoms become more noticeable. Although classic morning nausea usually resolves after the first trimester, in women prone to reactions associated with bile stasis, discomfort may persist throughout the entire pregnancy.

Reduction in insulin sensitivity reaches its peak in the third trimester. In women with genetic predisposition, low physical activity, excess body weight, or vitamin D deficiency, gestational diabetes may first manifest during this period. If disturbances in glucose levels arise specifically in the second or last trimester of pregnancy, this is considered an early marker of increased risk for glucose metabolism disorders in the coming years, even after pregnancy ends.

The digestive system functions at its slowest point of pregnancy during this period. Due to uterine pressure, acid reflux intensifies, post-meal heaviness may persist, and constipation becomes more pronounced.

The musculoskeletal system experiences maximal load. The center of gravity is shifted forward, lumbar lordosis increases, and ligaments become more mobile under the influence of relaxing. This intensifies back pain, increases strain on pelvic structures, and raises the tendency toward varicose veins and edema.

Nutrient requirements are at their peak: the fetus actively builds iron stores, the nervous system is developing, and the demand for DHA, choline, vitamin D, iron, magnesium, and amino acids increases. Even minor deficiencies can quickly become clinically significant.

What Should Be Checked Before Pregnancy

Once it is clear which systems are subjected to stress during pregnancy and which tests help assess their condition, the next step is to focus on those areas where the body may lack resources. The goal of preparation is to create conditions under which pregnancy is better tolerated and the child’s development occurs in the most favorable environment.

In the absence of serious pathology, correction does not need to be complex. In most cases, this involves working with nutrition, improving absorption, correcting deficiencies, and reducing the impact of factors that may overload the body.

Iron level and risk of anemia

• Ferritin, hemoglobin;
• Indicators of iron metabolism (serum iron, TIBC, transferrin saturation).

Vitamin B12, folate, and B-group vitamins

• Vitamin B12, folate;
• B-group vitamins - as indicated.

Thyroid gland

• TSH, FT4 / FT3;
• Anti-TPO, Anti-TG.

Vitamin D and other important nutrients

• Vitamin D;
• Vitamin A;
• Iodine (testing or dietary assessment);
• Magnesium, electrolytes, GFR;
• Zinc - as needed;
• Omega-3 (testing or dietary assessment).

Glucose level and risk of gestational diabetes

• Fasting glucose and insulin;
• HbA1c;
• Glucose tolerance curve - if needed.

Urinalysis and tendency to UTI

• Urinalysis;
• Urine culture - in case of UTI tendency;
• Creatinine and eGFR.

Gastrointestinal tract

• H. pylori - as indicated;
• Calprotectin or digestive panel - if symptoms are present;
• Microbiota tests - in chronic stool disturbances or bloating.

Infections that are important to know

• Vaginal culture in cases of recurrent BV or candidiasis.

General health status

• ECG;
• Lipid profile;
• Liver markers (ALT, AST, bilirubin, GGT, ALP);
• Complete blood count (CBC);
• Coagulation panel - in the presence of risk factors;

Nutrition and Hydration During Pregnancy

Nutrition and fluid intake during pregnancy supply the mother’s body with the materials and circulating blood volume required for placental formation, fetal growth, and maintenance of normal circulation. These processes operate together, since nutrient absorption, oxygen transport, and circulatory stability depend both on dietary quality and on adequate fluid volume. Hydration during pregnancy is an independent adaptive factor that directly affects blood volume, kidney function, vascular regulation, and tolerance to physical and physiological stress throughout all stages of pregnancy.

In early pregnancy (first trimester), the influence of diet is largely limited by tolerance. Hormonal changes reduce appetite, alter taste perception, and cause nausea. During this period, the body can temporarily rely on its own reserves, and only folate and vitamin B12 are of critical importance; these are usually provided by prenatal vitamins. At this stage, insufficient fluid intake intensifies manifestations of early pregnancy nausea. A reduction in plasma volume worsens blood supply to the stomach and liver, increases sensitivity to hormonal fluctuations, and makes nausea more pronounced. Dehydration slows gastric emptying, promotes ketone accumulation, and intensifies vomiting, forming a vicious cycle in which nausea becomes more severe. Even a moderate reduction in fluid intake increases weakness, dizziness, and sensitivity to odors, because the body’s adaptive responses operate against a background of altered vascular tone.

In the second trimester, the need for protein, fats, vitamins, and minerals increases, as fetal and placental tissues actively develop, and blood volume continues to expand. At the same time, fluid requirements rise: the kidneys function in a state of increased filtration, and stable plasma volume is necessary to maintain adequate blood volume pumped by the heart and sufficient blood flow between the uterus and the placenta. Insufficient fluid intake increases heart rate, reduces tolerance to physical activity, and makes hemodynamic adaptation less stable.

In the third trimester, metabolic load reaches its maximum. The fetus builds iron stores, the nervous system continues active development, and physiological insulin resistance increases the mother’s sensitivity to fluctuations in blood glucose. Nutrition becomes the primary source of stable energy and nutrients, particularly protein, fats, iron, magnesium, and choline. Omega-3 fatty acids are of particular importance, with the ratio shifted toward DHA: DHA is critical for the development of the fetal brain and retina, while EPA is necessary for the formation and maintenance of cell membranes and participates in the regulation of inflammatory processes in the mother. At the same time, fluid requirements increase further: expansion of blood volume and mechanical pressure of the uterus on vessels in the lower body require stable venous return and adequate plasma volume. Even minor disturbances in fluid balance intensify edema, provoke palpitations, and reduce tolerance to physical exertion.

Thus, nutrition and hydration form a unified system of processes that provide the mother’s body with the resources required for fetal growth, maintenance of blood volume, stability of vascular regulation, and full metabolic function. Their role changes as pregnancy progresses and reflects the physiological stages of adaptation.

Lifestyle and Physiological Load During Pregnancy

During pregnancy, familiar lifestyle elements - sleep, light physical activity, nutrition, and hydration - begin to play a more pronounced functional role, because it is through them that the body maintains stable circulation, uteroplacental blood flow, regulation of metabolism, and muscular stability. These processes do not prescribe universal routines, but they explain why the body responds to everyday loads differently than it did before pregnancy.

The need for sleep increases, because the body daily processes an increased volume of blood, maintains heightened activity of the endocrine system, and ensures continuous functioning of the placenta. During sleep, neural regulation stabilizes, vascular tension decreases, and adequate cardiac output is formed. Sleep deprivation increases heart rate acceleration, fatigue, and dizziness upon standing, because adaptive reserves during pregnancy are depleted more quickly, while recovery is required to maintain stable blood supply to both the mother and the fetus.

Physical activity becomes an important part of circulatory adaptation. During movement, venous return increases, the amount of blood ejected by the heart with each beat rises, and tissue perfusion improves, including within the uteroplacental circulation. For the fetus, this means a more stable supply of oxygen and nutrients. With reduced physical activity, venous stasis increases, edema becomes more pronounced, and tolerance to physical load worsens. At the same time, body mechanics change: the shift of the center of gravity, the effect of relaxin on ligaments, and the increasing load on the muscles of the back, pelvis, and abdominal wall require stable muscular tone. These muscles provide support for the spine and pelvis throughout pregnancy and participate in the mechanics of labor; their functional weakness makes the load more noticeable and reduces stability of muscles and joints.

Hydration affects plasma volume and kidney function, which already operate at an increased filtration rate in early pregnancy. When fluid balance decreases, circulating blood volume is reduced, which increases the tendency toward dizziness, tachycardia, and drops in blood pressure. Because placental blood flow depends on stable maternal hemodynamics, fluctuations in hydration are reflected in overall well-being more quickly than outside of pregnancy.

Conclusion

Preparation for pregnancy is a way to create conditions in advance under which the body can calmly withstand increased load and ensure full development of the child. Pregnancy changes the function of the heart, kidneys, liver, immune and hormonal systems, increases the need for vitamins and minerals, and makes the body more sensitive to deficiencies and subtle problems.

When these features are understood beforehand, it becomes clear why it is important before conception to stabilize levels of iron, B-group vitamins, vitamin D, iodine, and other nutrients, support thyroid and gastrointestinal function, reduce the risk of infections, and pay attention to overall health status.

Such preparation does not complicate the process; on the contrary, it helps reduce the risk of complications, improves the well-being of the future mother, and creates safer conditions for fetal development from the very first weeks. The more stable the body’s condition before pregnancy, the more predictable its course and the better the long-term outcomes for both the woman and the child.