Overview of Pregnancy

Pregnancy induces dramatic changes in a woman's body as it prepares to hold and nourish the fetus as it matures. In addition to the obvious physical changes that occur as the baby begins to grow, there are also numerous physiological changes that happen as the body works to support this new life.


In the mother's cardiovascular system, cardiac output increases significantly to be sure there is adequate blood flow to the uterus as the fetus and placenta begin to develop. The placenta is the main supply of nutrients to the fetus, and also helps carry waste products from away so that they may be excreted by the mother's kidneys. As the fetus develops and grows, it continues to place more demands on the mother's heart muscle. While the hearts normally beat harder and faster during exercise, it beats even harder and faster for women during pregnancy.

In order to accommodate the placenta and fetus, the total volume of blood also increases in pregnant women. The blood carries oxygen to all the tissues on a protein within the red blood cells called hemoglobin. In order for oxygen to bind hemoglobin, there must be iron present, so this increase in blood volume places new demands for iron on the body. Iron supplements are very important during pregnancy, as the demand for iron increases even more during the latter half of pregnancy.

Kidney and urinary functions also significantly change during pregnancy, as the mother's body processes the waste products generated by both her own body and that of the fetus. Increased urinary function is due in part to hormonal influences, but also the physical pressure due to the enlargement of the uterus. This physical pressure can change based on how the woman is positioned, which is one reason pregnant women frequently have to wake and urinate during the night.

The effects of pregnancy on the hormones are numerous. Very soon after conception, the embryo begins releasing human chorionic gonadotropon (hGC). hCG is a hormone that maintains the secretion of the hormone progesterone from the ovaries, which is critical for preventing further ovulation and maintaining pregnancy. hGC is the hormone typically measured during initial pregnancy tests. Progesterone induces the thickening of the uterine lining, enriching it with blood vessels so that it can support the growing fetus. Once the placenta develops, it also produces progesterone, as well as estrogen, which increases blood flow to the uterus. The placenta also produces a hormone called somatomammotropin, which changes the mother's metabolism to help nourish the baby. Somatomammotropin, which is structurally similar to human growth hormone, decreases the mother's sensitivity to insulin so that blood sugar levels can increase to help nourish the baby. The placenta adjusts the levels of this hormone in response to the body's nutritional state, increasing levels when blood sugars are chronically too low.

Pregnant mothers also experience respiratory changes. This is partly physical, as the fetus increases in size and changes the normal expanding of the lungs. The respiratory changes are also due to the increase of the hormone progesterone, which signals to the brain to lower carbon dioxide levels. In order to keep the blood oxygenated and the fetal tissues healthy, the need for oxygen increases considerably. To accommodate this, breathing becomes deeper and more rapid, which may lead to feeling out of breath, particularly during exertion.

There are also changes to the skin during pregnancy, some due to hormonal changes. Pink stretch marks can appear on the breasts and stomach due to rapid growth. There is sometimes darkening of the skin around the nipples or along a line down the middle of the abdomen (linea nigra), due to placental stimulation of melanin.

All these changes occur to rebalance the mother's physiology so that her body can accommodate the growing baby's every need.

Symptoms of Pregnancy

One of the symptoms of pregnancy that is often the first cue to the woman that she may be pregnant is a missed period. Some pregnant women initially experience light bleeding at the time when they would normally have a period, while others may not bleed at all (amenorrhea). Other factors that may also cause missed periods include low body weight, excessive exercise, or stress. Because the menstrual cycle is controlled by the timed release of particular hormones, hormonal imbalances may also cause a missed period. Stress can also cause a period to be skipped.

There are also changes to the breasts that occur during pregnancy, including swelling and tenderness similar to that which some women experience just before menstruation. These symptoms could simply indicate that menstruation will occur in a few days or may also be a result of hormonal imbalances, perhaps fooling the body into thinking it may menstruate. Oral contraceptives, which are combinations of hormones used to control ovulation, can also cause these breast changes.

More than half of pregnant women experience morning sickness during the first few months of their pregnancy. Nausea often occurs in the morning and subsides as the day progresses, though the waves of nausea may occur any time of day. The episodes of nausea may be mild or induce vomiting. The cause of morning sickness is incompletely understood, but there seems to be a correlation between estrogen levels and the development of morning sickness. Estrogen levels may increase up to one hundred times the normal levels during pregnancy, and women who get morning sickness appear to have more circulating estrogen. Morning sickness normally begins around the sixth week of pregnancy and subsides around the twelfth week. Other illnesses related to food poisoning, gastrointestinal disorders, or infections may potentially cause similar symptoms.

Early in pregnancy, many women often feel overwhelmingly tired. This fatigue is thought to be caused by the boost in progesterone levels. Energy is normally restored during the fourth month, coinciding with development of the placenta. Numerous other conditions can also lead to fatigue, including anemia, insufficient exercise, lack of sleep (possibly sleep disorder), or excessive busyness. Fatigue can also be a sign of chronic illness.

Although some women feel a sense of elation during pregnancy, yhe hormonal changes early in pregnancy can also cause mood changes, somewhat similar to those associated with premenstrual syndrome (PMS). These include mood swings, weepiness, and irritability. Clearly, these emotional changes can potentially be caused by stress.

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