Pregnancy triggers thousands of complex and profound biological changes. Structures and functions develop rapidly with time-critical energy and nutrient needs, according to Judith Brown in "Nutrition Through the Life Cycle." Increased secretion of various hormones during pregnancy brings about an elevated basal metabolic rate and alterations in how carbohydrates, protein and fat are used by your body, as described by Mary Mitchell in "Nutrition Across the Life Span."
Changes in maternal body composition and functions begin in earnest within a week after conception. Some of the resulting symptoms you may notice in the first few weeks of dramatic change include nausea or morning sickness, tender breasts, dizziness, food cravings, increased urination, fatigue and mood swings.
Body Composition
Dramatic changes in body composition occur during pregnancy. Increased maternal fat stores, body fluid and maternal and fetal protein contribute to an increase in body weight of 15 to 40 pounds. Included in these changes are increased mammary, uterine, kidney and heart tissue volume. Physiological changes in the first half of pregnancy increase the capacity of the mother's body to deliver relatively large quantities of blood, oxygen and nutrients to the fetus in the second half of pregnancy. Approximately 10 percent of fetal growth occurs in the first half of pregnancy and 90 percent occurs in the second half, according to "Nutrition Across the Life Span."
Blood Volume
Your plasma blood volume increases by about 50 percent. This volume increase, or hypervolemia, beginning in the first trimester, is needed to provide extra blood flow to the uterus, provide for metabolic needs of the fetus and increased perfusion of blood to the kidneys and other organs.
Cardiovascular System
Your cardiac output increases by approximately 40 percent during pregnancy. This increase is accompanied by an increase in your stroke volume and pulse rate. This rate is reached between weeks 20 and 24 of your pregnancy and remains at this higher level until delivery, as reported by Mary Mitchell.
Gastrointestinal System
Your stomach empties more slowly, and the slower transit of food through your intestinal tract enhances your ability to absorb nutrients. As your colon absorbs more water, you may experience constipation. Slower gastric emptying and relaxing of muscle between your esophagus and stomach may lead to gastric reflux.
Respiration
You will use about 20 percent more oxygen because of your increased basal metabolic rate and your increased body size. As your growing uterus begins to press against your diaphragm, decreasing the space for your diaphragm to expand, your respiratory rate will increase to maintain adequate oxygen levels.
Kidney
Blood flow to your kidneys and clearance of waste products are increased. Your kidneys filter blood at a rate about 50 percent above normal beginning in early pregnancy, and the rate remains high until delivery.
References
- "Nutrition Through the Life Cycle, Third Edition"; Judith E. Brown; 2008
- "Nutrition Across the Life Span"; Mary Kay Mitchell; 2003
- "Understanding Nutrition, Ninth Edition"; Eleanor Noss Whitney and Sharon Rady Rolfes; 2002
- Mayo Clinic: Symptoms of pregnancy: What happens right away
- American Congress of Obstetricians and Gynecologists: Months 1 and 2: Your Growing Baby
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