Phenomenal alterations in metabolism occur during pregnancy. The many visible changes that occur in a woman's body during pregnancy are accompanied by other anatomic, metabolic and physiologic changes to provide for the demands of the growing infant, according to Mary Mitchell in "Nutrition Across the Life Span." Maternal physiological changes begin within a week after conception and proceed in sequence throughout the pregnancy to provide the growing fetus with energy, nutrients and oxygen for rapid growth and development.
History
Maternal changes in physiology are so profound that doctors once considered them abnormal and in need of correction. Doctors once prescribed low-sodium diets in an effort to reduce fluid retention, severely restricted weight gain and prescribed excessive levels of iron and other supplements to bring blood nutrient levels back up to what was considered "normal," according to Judith Brown in "Nutrition Through the Life Cycle." Today, doctors know that what is normal physiological status for non-pregnant women does not apply to women who are pregnant.
Function
The physiologic and metabolic changes of pregnancy affect virtually every organ system of the mother. These changes allow the mother's body to support the growing uterus and growing and developing fetus as well as to withstand labor and postpartum changes. The many accommodations in the mother's body are required to ensure a healthy pregnancy and successful birth outcome.
Anatomic Changes
Beyond the most obvious physical changes such as a weight gain of 15 to 40 lbs. and altered body shape, dramatic changes take place in a woman's body during pregnancy, according to Eleanor Whitney and Sharon Rolfes in "Understanding Nutrition." Her uterus and supporting muscles increase in both strength and size. Her joints become more flexible to prepare for childbirth. Extra water retention may cause her feet and ankles to swell. Her breasts grow in preparation for lactation.
Metabolic Changes
The amount of blood in an expectant mother's body increases by 50 percent to carry additional nutrients and other needed materials. Hormone changes result in altered use of carbohydrates, protein and fat, according to Mary Mitchell in "Nutrition Across the Life Span." Fat becomes a major source of maternal fuel and glucose the main source of fetal energy.
Her cardiac output increases by 30 percent to 50 percent with an increase in stroke volume and pulse rate. She will have a slight increase in respiratory rate with a higher volume of gases exchanged with each breath. Her metabolism changes include an increase of about 15 percent in basal metabolic rate and an increase in oxygen-carrying capacity of the blood. Blood flow through the kidneys increases along with an increase in the kidney's filtration rate.
Physiologic Changes
The expectant mother may experience an increase in appetite, nausea and vomiting and altered taste. She will absorb more nutrients from food and her stomach will empty more slowly. Her body will experience an increase in protein, fat stores and body fluids. She will excrete more glucose, amino acids and water-soluble vitamins. She may experience constipation as her colon absorbs more water. Hormones that cause all these changes may also affect her mood.
Considerations
Pregnancy weight gain affects birth weight and long-term health outcomes. Weight gain recommendations are based on prepregnancy weight status.
Variations in fetal growth and development generally relate to environmental factors, such as energy, nutrient and oxygen availability.
The fetus is not a parasite, according to Judith Brown in "Nutrition Through the Life Cycle." It cannot take nutrients from the mother's body at the mother's expense.
References
- "Nutrition Across the Life Span"; Mary Kay Mitchell; 2003
- "Nutrition Through the Life Cycle, Third Edition"; Judith E. Brown; 2008
- "Understanding Nutrition, Ninth Edition"; Eleanor Noss Whitney and Sharon Rady Rolfes; 2002
- American Congress of Obstetricians and Gynecologists: How your baby grows during pregnancy
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