Expecting Mothers: Physiological Changes

06 January, 2020
Expecting mothers experience many anatomical and physiological changes. In this article, we'll take look at what happens and why.

Anatomical and physiological changes in expecting mothers result from the new needs experienced by both her body and the fetus. These changes affect every aspect of the body, and not all women experience them the same way. With this in mind, we offer a look at what expecting mothers can expect during pregnancy.

Anatomical and physiological changes in expecting mothers

The reproductive system

Of all the organs involved in the reproductive system, the uterus undergoes the most changes. It increases in size, reaching a capacity of approximately five liters and a weight of 1,100 grams by the end of gestation.

In non-pregnant women, the uterus is located within the pelvis. During pregnancy, it becomes an abdominal organ and, as it increases in size, its bottom section can be felt through the abdomen.

Uterine growth is one of the most commonly used measures for monitoring pregnancy. This growth results from the hormones estrogen and progesterone, and from the distension created by fetal growth.

As the pregnancy progresses, blood flow to the uterus also increases in order to adequately perfuse the placenta and, consequently, the fetus.

Expecting Mothers: Physiological Changes

Other changes in the reproductive system

In the cervix, the cervical glands increase their secretions, resulting in the mucus plug. This serves as a defense against microorganisms entering the vagina.

The cervix also increases its vascularization and becomes swollen. It also softens (Hegar sign) and takes on a slightly bluish color.

Vascularization also increases in the vaginal and vulvar region, causing the tissues to become slightly edematous and cyanotic (Chadwick’s sign).

In preparation for childbirth, the vagina becomes more elastic, and it increases the secretion of a thick, whitish discharge. The acidic pH of this discharge protects against a variety of infections, but it’s also a fungal culture medium. This causes frequent fungal infections (candidiasis) during pregnancy.

Until approximately seven weeks of pregnancy, one of the ovaries contains the corpus luteum. This maintains the hormonal production that allows the pregnancy to progress until the placenta becomes the main hormone producer.

In addition, the breasts increase in size, with the pigmentation of the areola and nipple increasing and small elevations (Montgomery tubercles) appearing on the nipple. These tubercles are in fact hypertrophied sebaceous glands. Also, the circulus venosus of Haller appears. The first milk secretions may appear around the fourth month of pregnancy.

As you can see, expecting mothers experience a host of changes to their reproductive systems.

Skin

Hormonal changes produce the majority of the changes to the skin. Expecting mothers may experience:

  • Hyperpigmentation in the linear alba of the abdomen, the nipples, the areolae, and the vulva.
  • Facial blotches (chloasma gravidarum).
  • Spider angiomas on the face, neck, extremities, and chest.
  • Stretch marks on the breasts, abdomen, and buttocks.
  • Increased activity of the sweat and sebaceous glands.

Metabolic changes

At a metabolic level, expecting mothers may also undergo the following changes:

  • Weight gain. This is primarily due to the fetus and its annexes, increased blood volume and interstitial fluid, the growth of the uterus and breasts, and new fat deposits.
  • Carbohydrate metabolism. Pregnancy increases the production of insulin, as well as the tissues’ resistance to their effects. Peripheral glucose utilization increases, while glucose production in the liver decreases.
  • Fat metabolism. During the second trimester, the synthesis and absorption of cholesterol and triglycerides increase, as does the accumulation of fat in the tissues.
  • Protein metabolism. The growth of fetal tissues creates a high demand for protein.
  • Water metabolism. Up to seven liters of water is retained and distributed among the mother, the fetus, and the fetal annexes.

The respiratory system

During pregnancy, increased estrogen causes hyperaemia in the mucosa of the nasal passages. This results in episodes of rhinitis, nasal congestion, and nosebleeds.

The ribcage also undergoes modifications during pregnancy. The diaphragm rises and the width of the thorax increases. These changes are due to uterine growth and the relaxation of the intercostal ligaments due to hormones.

Expecting Mothers: Physiological Changes

There are also changes in terms of pulmonary function:

  • The functional residual capacity and total capacity decrease.
  • Inspiratory capacity increases.
  • Breathing rate increases slightly, especially in the third trimester.

Expecting mothers: the digestive system

It’s common for pregnant women to suffer from nausea and vomiting. This is mainly due to the presence and activity of B-hCG and progesterone (hormones that act during pregnancy).

The mouth also undergoes changes due to hormonal activity. The salivary pH drops, which can alter the bacterial flora. If proper oral hygiene isn’t practiced, this can result in tooth decay.

In addition, estrogen increases vascularization, which can lead to bleeding and inflammation of the gums.

Due to its increased size, the uterus displaces the abdominal organs. This leads to increased intra-abdominal pressure. Progesterone relaxes the GI tract so that bowel transit slows. This can cause:

  • Heartburn.
  • Constipation.
  • Slow and heavy digestion.
  • Hiatal hernia.

Progesterone activity also affects the gallbladder. It empties more slowly, which leads to thicker bile. These changes can increase the likelihood of gallstones.

Expecting mothers: the urinary system

In pregnancy, the kidneys increase in size due to increased vascularization, interstitial volume, and dead spaces. In addition, the renal pelvis and ureters dilate.

These changes are more pronounced in the right kidney due to the rotation of the uterus. They can be seen beginning in the first trimester. Also, they cause urinary stasis, which can lead to infections and kidney stones.

The uterus increases intravesical pressure which, when combined with increased urinary output, results in a rise in daily urination.

The endocrine system

In expecting mothers, changes occur in terms of the segregation of different hormones, as well as the release of new ones. These are some of the hormones that play a significant role during pregnancy.

Human chorionic gonadotropin (HCG)

This is a hormone produced by the placenta, with B-hCG the subunit that most affects pregnancy. Levels are very high during the first trimester, before decreasing and remaining stable through the rest of pregnancy.

This hormone influences fetal growth, maintaining the corpus luteum until the placenta is able to produce enough steroids. It also stimulates the fetal testicles to produce testosterone.

Finally, HCG is the hormone that pregnancy tests detect, either in blood or in urine.

Expecting Mothers: Physiological Changes

Placental lactogen (PL)

This is another placental hormone. Its purposes are to increase lipolysis, increase insulin resistance, decrease gluconeogenesis, and increase breast tissue proliferation.

Estrogen and progesterone

Also produced by the placenta. They intervene in most of the changes that occur during pregnancy.

Gonadotropin-releasing hormone (GnRH)

This hypothalamic hormone affects the growth of the placenta, and its levels increase during pregnancy.

Prolactin

This is a pituitary hormone. Its levels increase as pregnancy progresses to prepare the woman’s body for breastfeeding.

Thyrotropic Hormone (TSH)

This hormone is produced in the thyroid gland. Its levels drop slightly during the first trimester as HCG increases (they share a similar structure). Afterward, its levels return to normal.

Expecting mothers: the cardiovascular system

In expecting mothers, blood volume increases by 1,500 – 1,700 ml. This rise is notable, since it increases the plasma volume more than the cell volume, leading to hemodilution and physiologic anemia.

This increase in blood volume serves different function during pregnancy:

  • Protects against the blood loss experienced by the mother during childbirth.
  • Satisfies new metabolic demands.
  • Protects against the damaging effects of impaired venous return during pregnancy.

In addition, the number of leukocytes rises, while platelets may decrease slightly. Coagulation factors increase while fibrinolytic activity decreases. This, combined with the blood stasis produced by the uterus with respect to venous return, increases the risk of thromboembolism.

At an anatomical level, the diaphragm rises and moves the heart forward and to the left. Cardiac output (CO) increases, as does heart rate, which goes up by 15 – 20 beats per minute.

Lastly, blood pressure values don’t change during pregnancy, and may even decrease in some cases.

Other anatomical and physiological changes in expecting mothers

Bones

Pregnant women absorb more calcium and phosphorus, while mobilizing that amount already contained in their bones to allow for proper fetal development. After delivery, bone density returns to normal. It’s proven that pregnancy isn’t a risk factor for osteoporosis in the future.

Musculoskeletal system

The spine accentuates its inward curve in order to adapt to weight gain. Vertebral nerve roots can be compressed or distended. These changes can lead to lower back pain or neuralgia.

Expecting Mothers: Physiological Changes

Immune system

During pregnancy, certain immune system functions are suppressed in order to allow a “foreign body” (the embryo) to reside within the body.

Sexuality

The aforementioned changes can influence a woman’s sexuality. Increased vascularization of the genital region leads to heightened sensitivity. This may result in greater satisfaction, or it may prove irritating.

In normal pregnancies, the contractions generated in the uterus after an orgasm won’t trigger birth due to their low intensity.

Final thoughts for expecting mothers

During your pregnancy, don’t hesitate to ask your midwife or gynecologist about any concerns you may have about the changes your body will experience.

  • Espinilla Sanz, B., Tomé Blanco, E., Sadornil Vicario, M., Albillos Alonso, L. (2016). Anatomía y fisiología del embarazo. Manual de obstetricia para matronas. 2nd ed. Valladolid: DIFÁCIL; 2016. 53-64.