Anne W. Hansen 
Pregnancy brings a variety of changes to the body. They can range from common and expected changes, such as swelling and fluid retention, to less familiar ones such as vision changes. Read on to learn more about them.
Hormonal Changes During Pregnancy
The hormonal and physiological changes that come with pregnancy are unique.
Pregnant women experience sudden and dramatic increases in estrogen and progesterone. They also experience changes in the amount and function of a number of other hormones. These changes do not just affect mood. They can also:
- create the “glow” of pregnancy
- significantly aid in the development of the fetus
- alter the physical impact of exercise and physical activity on the body
Estrogen and progesterone changes
Estrogen and progesterone are the chief pregnancy hormones. A woman will produce more estrogen during one pregnancy than throughout her entire life when not pregnant. The increase in estrogen during pregnancy enables the uterus and placenta to:
- improve vascularization (the formation of blood vessels)
- transfer nutrients
- support the developing baby
In addition, estrogen is thought to play an important role in helping the fetus develop and mature.
Estrogen levels increase steadily during pregnancy and reach their peak in the third trimester. The rapid increase in estrogen levels during the first trimester may cause some of the nausea associated with pregnancy. During the second trimester, it plays a major role in the milk duct development that enlarges the breasts.
Progesterone levels also are extraordinarily high during pregnancy. The changes in progesterone cause a laxity or loosening of ligaments and joints throughout the body. In addition, high levels of progesterone cause internal structures to increase in size, such as the ureters. The ureters connect the kidneys with the maternal bladder. Progesterone is also important for transforming the uterus from the size of a small pear — in its non-pregnant state to a uterus that can accommodate a full-term baby.
Pregnancy Hormones and Workout Injuries
While these hormones are absolutely critical for a successful pregnancy, they also can make exercise more difficult. Because the ligaments are looser, pregnant women may be at greater risk for sprains and strains of the ankle or knee. However, no studies have documented an increased rate in injury during pregnancy.
A pregnant woman’s entire posture changes. Her breasts are larger. Her abdomen transforms from flat or concave to very convex, increasing the curvature of her back. The combined effect shifts the center of gravity forward and may lead to changes in her sense of balance.
Weight Gain, Fluid Retention, And Workout
Weight gain in pregnant women increases the workload on the body from any physical activity. This additional weight and gravity slow down the circulation of blood and bodily fluids, particularly in the lower limbs. As a result, pregnant women retain fluids and experience swelling of the face and limbs. This water weight adds another limitation on exercise. Learn about natural treatments for swollen hands.
Many women begin to notice slight swelling during the second trimester. It often continues into the third trimester. This increase in fluid retention is responsible for a significant amount of weight gain women experience during pregnancy. Tips for easing swelling include:
- rest
- avoid long periods of standing
- avoid caffeine and sodium
- increase dietary potassium
Weight gain is usually the primary reason that the body can’t tolerate pre-pregnancy levels of exercise. This even applies to the seasoned, elite, or professional athlete. Round ligament strain, increased size of the uterus, and pelvic instability from laxity of the ligaments may lead to increased discomfort during exercise.
Sensory Changes
Pregnancy can dramatically alter how a woman experiences the world through sight, taste, and smell.
Vision changes
Some women experience vision changes during pregnancy, characterized by increased nearsightedness. Researchers don’t know the precise biological mechanisms behind changes in vision. Most women return to prepregnancy vision after giving birth.
Common changes during pregnancy include blurriness and discomfort with contact lenses. Pregnant women often experience an increase in intraocular pressure. Women with preeclampsia or gestational diabetes may be at an elevated risk of rare eye problems, such as retinal detachment or vision loss.
Taste and smell changes
Most women experience changes in their sense of taste during pregnancy. They typically prefer saltier foods and sweeter foods than non-pregnant women. They also have a higher threshold for strong sour, salty, and sweet tastes. Dysgeusia, a decrease in the ability to taste, is most commonly experienced during the first trimester of pregnancy.
Certain taste preferences may vary by trimester. Although many women experience a dulled sense of taste for a short period of time postpartum, they typically regain full taste capability after pregnancy. Some women also experience a metallic taste in the mouth during pregnancy. This can aggravate nausea and may indicate a nutrient imbalance. Learn more about impaired taste.
At times, pregnant women also report changes in their sense of smell. Many describe a heightened awareness and sensitivity to a variety of odors. There’s little consistent and reliable data indicating that pregnant women actually notice and identify certain odors and intensity of odors more than their non-pregnant counterparts. Nevertheless, the vast majority of pregnant women report a perceived increase in their own sensitivity to odors.
Breast And Cervical Changes
Hormonal changes, which begin in the first trimester, will lead to many physiological changes throughout the body. These changes help prepare the mother’s body for pregnancy, childbirth, and breastfeeding.
Breast changes
Pregnant women’s breasts often undergo a series of significant changes during pregnancy as their bodies prepare to supply milk to the newborn baby. Pregnancy hormones that affect skin pigmentation often darken the areola. As the breasts grow, pregnant women may experience tenderness or sensitivity and notice that the veins are darker and the nipples protrude more than before pregnancy. Some women may develop stretch marks on the breasts, particularly if they undergo rapid growth. Many women will also notice an increase in the size of the nipple and areola.
Small bumps on the areolas often appear. Most women will begin producing, and even “leaking,” small amounts of a thick, yellowish substance during the second trimester. This substance is also known as colostrum. In addition to producing the colostrum for the baby’s first feeding, milk ducts in the breasts expand in preparation for producing and storing milk. Some women may notice small lumps in the breast tissue, which can be caused by blocked milk ducts. If the lumps don’t disappear after a few days of massaging the breast and warming it with water or a washcloth, a doctor should examine the lump at the next prenatal visit.
Cervical changes
The cervix, or the entry to the uterus, undergoes physical changes during pregnancy and labor. In many women, the tissue of the cervix thickens and becomes firm and glandular. Up to a few weeks before giving birth, the cervix may soften and dilate slightly from the pressure of the growing baby.
In early pregnancy, the cervix produces a thick mucus plug to seal off the uterus. The plug is often expelled in late pregnancy or during delivery. This is also called bloody show. Mucous streaked with a small amount of blood is common as the uterus prepares for labor. Prior to delivery, the cervix dilates significantly, softens, and thins, allowing the baby to pass through the birth canal. Learn more about the stages of labor and how they affect the cervix.
Changes In The Hair, Skin, And Nails
Many women will experience changes in the physical appearance of their skin during pregnancy. Although most are temporary, some — such as stretch marks — can result in permanent changes. In addition, women who experience some of these skin changes during pregnancy are more likely to experience them again in future pregnancies or even while taking hormonal contraceptives.
Hair and nail changes
Many women experience changes in hair and nail growth during pregnancy. Hormone changes can sometimes cause excessive hair shedding or hair loss. This is especially true in women with a family history of female alopecia.
But many women experience hair growth and thickening during pregnancy and may even notice hair growth in unwanted places. Hair growth on the face, arms, legs, or back can occur. Most changes in hair growth return to normal after the baby is born. It’s common, however, for hair loss or increased shedding to occur up to a year postpartum, as hair follicles and hormone levels regulate themselves without the influence of pregnancy hormones.
Many women also experience faster nail growth during pregnancy. Eating well and taking prenatal vitamins adds to the growth hormones of pregnancy. Although some may find the change desirable, many may notice increased nail brittleness, breakage, grooves, or keratosis. Healthy dietary changes to increase nail strength can help prevent breakage without the use of chemical nail products.
Pregnancy and Hyperpigmentation
The vast majority of pregnant women experience some type of hyperpigmentation during pregnancy. This consists of a darkening in skin tone on body parts such as the areolas, genitals, scars, and the linea alba (a dark line) down the middle of the abdomen. Hyperpigmentation can occur in women of any skin tone, although it’s more common in women with darker complexions.
In addition, up to 70 percent of pregnant women experience a darkening of skin on the face. This condition is known as melasma, or the “mask” of pregnancy. It can be worsened by sun exposure and radiation, so a broad-spectrum UVA/UVB sunscreen should be used daily during pregnancy. In most cases, melasma resolves after pregnancy.
Stretch marks
Stretch marks (striae gravidarum) are perhaps the most well-known skin change of pregnancy. They’re caused by a combination of physical stretching of the skin and the effects of hormone changes on the skin’s elasticity. Up to 90 percent of women develop stretch marks by the third trimester of pregnancy, often on the breasts and abdomen. Although the pinkish-purple stretch marks may never fully disappear, they often fade to the color of surrounding skin and shrink in size postpartum. Stretch marks can itch, so do apply creams to soften and reduce the urge to scratch and possibly damage the skin.
Mole and freckle changes
The hyperpigmentation caused by changes in hormones during pregnancy can cause changes in the color of moles and freckles. Some darkening of moles, freckles, and birthmarks can be harmless. But it’s always a good idea to see a dermatologist or physician about changes in size, color, or shape.
Pregnancy hormones can also cause the appearance of dark patches of skin that are often unpreventable. Although most skin pigmentation changes will fade or disappear after pregnancy, some changes in mole or freckle color may be permanent. It’s a good idea to have a skin check for potential skin cancer or pregnancy-specific skin conditions if you notice any changes.
Circulatory System Changes
The following are common during pregnancy:
- huffing and puffing while climbing stairs
- feeling dizzy after standing quickly
- experiencing changes in blood pressure
Because of rapid expansion of the blood vessels and the increased stress on the heart and lungs, pregnant women produce more blood and have to utilize more caution with exercise than non-pregnant women.
Heartbeat and blood volume during pregnancy
During the second trimester of pregnancy, the mother’s heart at rest is working 30 to 50 percent harder. Most of this increase results from a more efficiently performing heart, which ejects more blood at each beat. Heart rate may increase up to 15 to 20 percent during pregnancy. It’s not uncommon to approach 90 to 100 beats per minute in the third trimester. Blood volume increases progressively during pregnancy until the last month. The volume of plasma increases 40-50 percent and red blood cell mass 20-30 percent, creating a need for increased iron and folic acid intake.
Blood pressure and exercise
There are two types of circulatory changes that may have an impact on exercise during pregnancy. Pregnancy hormones can suddenly affect the tone in blood vessels. A sudden loss of tone may result in the feeling of dizziness and perhaps even a brief loss of consciousness. This is because the loss of pressure sends less blood to the brain and central nervous system.
Additionally, vigorous exercise may lead to decreased blood flow to the uterus while diverting blood to muscles. However, this has not been shown to have a long-term impact on the baby. Furthermore, there’s evidence to suggest that individuals who exercise have improved blood supply to the placenta at rest. This may be beneficial to placental and fetal growth and weight gain.
Dizziness and fainting
Another form of dizziness can result from lying flat on the back. This dizziness is more common after 24 weeks. However, it can happen earlier during multi-fetal pregnancies or with conditions that increase amniotic fluid.
Lying flat on the back compresses the large blood vessel leading from the lower body to the heart, also known as the vena cava. This decreases blood flow to and from the heart, leading to a sudden and dramatic decline in blood pressure. This can cause dizziness or loss of consciousness.
After the first trimester, it’s not recommended to do exercises that involve lying on the back due to the impact from blood vessel compression. Lying on the left side may help relieve dizziness and is a healthy position for sleep.
Women experiencing any of these conditions, particularly during exercise, should consult their doctor.
Respiratory And Metabolic Changes
Pregnant women experience increases in the amount of oxygen they transport in their blood. This is because of increased demand for blood and the dilation of blood vessels. This growth forces increases in metabolic rates during pregnancy, requiring women to up energy intake and use caution during periods of physical exertion.
Breathing and blood oxygen levels
During pregnancy, the amount of air moved in and out of the lungs increases by 30 to 50 percent due to two factors. Each breath has a greater volume of air, and the rate of breathing increases slightly. As the uterus enlarges, the room for movement of the diaphragm may be limited. Therefore, some women report the feeling of increased difficulty in taking deep breaths. Even without exercise, these changes may cause shortness of breath or the feeling of being “air hungry.” Exercise programs may increase these symptoms.
Overall, pregnant women have higher blood oxygen levels. Studies have shown that pregnant women consume more oxygen at rest. This does not seem to have an impact on the amount of oxygen available for exercise or other physical work during pregnancy.
Metabolic rate
Basal or resting metabolic rate (RMR), the amount of energy the body expends while at rest, increases significantly during pregnancy. This is measured by the amount of oxygen used during periods of total rest. It helps estimate the amount of energy intake required to maintain or gain weight. Changes in metabolic rates explain the need to increase calorie consumption during pregnancy. The body of a pregnant woman slowly increases its energy requirements to help fuel the changes and growth taking place in both the mother and baby.
Metabolic rates increase substantially by just 15 weeks’ gestation and peak in the third trimester during the greatest growth phase. This increased metabolic rate may put pregnant women at a higher risk of hypoglycemia, or low blood sugar. Although the metabolic rate may drop slightly as the pregnancy reaches term, it remains elevated over prepregnancy levels for several weeks postpartum. It will remain elevated for the duration of breastfeeding in women producing milk.
Body temperature changes
An increase in basal body temperature is one of the first hints of pregnancy. A slightly higher core temperature will be maintained through the duration of pregnancy. Women also have a greater need of water during pregnancy. They can be at higher risk of hyperthermia and dehydration without caution to exercise safely and remain hydrated.
Hyperthermia
Heat stress during exercise creates concern for two reasons. First, an increase in the mother’s core temperature, as in hyperthermia, can be harmful to the baby’s development. Second, loss of water in the mother, as in dehydration, can decrease the amount of blood available to the fetus. This can lead to increased risk of preterm contractions.
In non-pregnant women, moderate aerobic exercise causes significant increases in core body temperature. Pregnant women, whether they exercise or not, experience a general increase in base metabolic rate and core temperature. Pregnant women regulate their core temperature very efficiently. Increased blood flow to the skin and the expanded skin surface release increased body heat.
It’s been shown that pregnant women do not have as much of an increase in body temperature during exercise as those who are not pregnant. However, pregnant women should avoid exercising in non-breathable clothing and in very hot or humid conditions, since the impact of hyperthermia can be severe. The following may help reduce the risk of overheating while exercising:
- use fans during indoor activity
- exercise in the pool
- wear light-colored, loose-fitting clothing
Dehydration
Most women who exercise for 20 to 30 minutes or who exercise during hot and humid weather will sweat. In pregnant women, loss of bodily fluids from sweat can decrease the blood flow to the uterus, the muscles, and some organs. The developing fetus needs a constant supply of oxygen and nutrients carried through the blood, so injury may result from a lack of fluid.
In most conditions, uterine oxygen consumption is constant during exercise and the fetus is safe. However, exercising can be dangerous for women with pregnancy-induced hypertension. That’s because this condition limits uterine blood volume as the vessels clamp down and deliver less blood to the area.
If you’re cleared for exercise during pregnancy, be sure to follow common-sense tips. Avoid excessive heat and humidity and rehydrate, even when you’re not thirsty.
