Physiologic Changes in the Pregnant Female

Pregnancy causes many changes in the physiology of the pregnant female. Physiologic changes occur in the cardiovascular, hematologic, respiratory, gastrointestinal, genitourinary, endocrine and orofacial systems. Some of these physiologic changes can lead to medical complications during pregnancy.

In pregnant females, aged 11 through 15 years, medical complications in the mother and fetus occur more frequently than those aged 20 to 22 years. These include delivery of low birth weight infants, increased neonatal death rate, pregnancy induced hypertension, anemia, sexually transmissible diseases and premature delivery.11

Additionally, the presence of the social risk factor of lack or limited parental involvement can lead the adolescent to the initiation of smoking. Women who smoke may have increased risk for ectopic pregnancy, spontaneous abortion and preterm delivery. Infants born to women who smoke are more likely to be small for gestational age and low birth weight. Maternal smoking during pregnancy can lead to intellectual disability and birth defects such as cleft palate in the child. There is increased risk of stillbirths and neonatal deaths and sudden infant death syndrome. Infants and children exposed to second hand smoke have higher rates of lower respiratory illness, middle ear infections, asthma and caries in the primary dentition.12

During all pregnancies, the cardiovascular changes the pregnant patient exhibits are increases in blood volume and cardiac output, decrease in peripheral vascular resistance and blood pressure, as compared with the non pregnant patient. This can lead to hypotensive episodes during the second and third trimesters while in the supine position, due to decreased venous return to the heart from the compression of the interior vena cava by the gravid uterus (supine hypotensive syndrome) and increased vasodilation due to increased levels of progesterone, prostaglandins and nitric oxide.

Respiratory changes during pregnancy occur to accommodate the increasing size of the developing fetus and increased maternal-fetal oxygen requirements. The growing fetus pushes the diaphragm up by 3-4 cm causing an increase in intrathoracic pressure. This leads to an increase in chest circumference and a 15% to 20% reduction in functional residual capacity. These changes can lead to hyperventilation, dyspnea and hypoxemia as the pregnancy progresses. The conditions are exacerbated when the pregnant patient is placed in a supine position.

Changes in the circulatory system include an increase in the number of erythrocytes and leukocytes, erythrocyte sedimentation rate and clotting factors, leading to an increased state of coagulation. This hypercoagulable state increases the risks for thromboembolism at a rate of five times that of non pregnant patients. Patients exhibiting thromboembolism are treated with heparin, aspirin or intravenous immunoglobulin therapy.

The predominant gastrointestinal changes are nausea, vomiting and heartburn due to mechanical changes resulting from the enlarging fetus combined with hormonal changes. Two thirds of patients complain of vomiting, with the peak frequency at the end of the first trimester. Heartburn occurs in 30% to 50% of pregnant women. Reflux occurs as a result of increased intragastric pressure due to the growing fetus, slower gastric emptying rate and decreased resting pressure of the lower gastroesophagus sphincter. The nausea and vomiting during pregnancy can be attributed to the effects of estrogen and progesterone. Liver dysfunction may lead to preeclampsia, a combination of hypertension, proteinuria (hemolysis, elevated liver enzymes, low platelets), and obstructive cholestasis. The exact cause of preeclampsia has not been identified. Pregnant women with elevated blood pressure should be referred to their primary physician or obstetrician for possible development of preeclampsia.

The principal renal and genitourinary changes in pregnant patients are increased glomerular filtration rate, biochemical changes in the urine and blood, more frequent need to urinate and a greater risk of urinary tract infection. When drugs with renal clearance are prescribed, doses may need to be increased to compensate for their more rapid clearance. It recommended the patient empty their bladder just prior to starting the dental procedure.

The hormones most responsible for physiologic changes during pregnancy are the female sex hormones estrogen, progesterone and human gonadotrophin, which are secreted primarily by the placenta. There is also an increase in thyroxine, steroids and insulin levels. However, about 4% of pregnant women are unable to produce sufficient levels of insulin to overcome the antagonistic action of estrogen and progesterone and thus develop gestational diabetes.

Orofacial changes encompasses both hard and soft tissue. The predominant hard tissue change is an increase in the caries rate associated with increased snacking frequency of refined carbohydrates. Morning sickness and the accompanying vomiting reflux contributes to perimyolisis, erosion of the lingual surfaces of teeth caused by exposure to gastric acids. Pregnancy related xerostomia may occur, leading to complaints of dry mouth.

Figure 1. Perimyolisis - erosion of the lingual surfaces of the teeth caused by exposure to gastric acids.
Image: Teeth showing erosion of the lingual surfaces.
Image courtesy of Dr. Kim Laurell.

Soft tissue changes include; gingivitis, gingival hyperplasia, pyogenic granuloma, salivary changes and increased facial pigmentation. Elevated estrogen levels increases capillary permeability, predisposing pregnant women to gingivitis and gingival hyperplasia. Pregnancy does not cause periodontal disease but can exacerbate an existing condition. Increased angiogenesis, due to sex hormones coupled with gingival irritation caused by local factors (plaque) can cause pyogenic granulomas in less than 5% of patients during the first and second trimesters. Most granulomas resolve within 3 months of the child’s birth. Increases in salivary estrogen lead to the proliferation and desquamation of oral mucosal cells providing conditions for bacterial growth which can predispose pregnant woman to dental caries. Studies of the relationship of periodontitis during pregnancy and its relationship to preterm, low birth weight infants have produced conflicting results and continues to be studied. Thus, good oral hygiene should be encouraged for the pregnant woman to reduce inflammatory oral changes.13

Figure 2. Pregnancy gingivitis.
Image: Gums with gingivitis.
Image courtesy of Dr. Géza Terézhalmy.
Figure 3. Pregnancy tumor.
Image: Tumor on a gum.
Image courtesy of Dr. Géza Terézhalmy.

As mentioned earlier, the rate of complications due to these physiologic changes in adolescent pregnant females and their offspring occur more frequently than in pregnant adults. In addition to the changes and complications described above, there is delivery of low birth infants, increased neonatal death rate and increase mortality rate for the mother.14 Deliveries to pregnant adolescents are approximately twice as likely to be of low birth weight and to be born prematurely. The neonatal death rate (within 28 days of birth) of deliveries to adolescents is almost triple that of deliveries to adults, while the adolescent maternal mortality rate is double the adult rate. Additional complications include pregnancy induced hypertension, anemia, sexually transmitted diseases and premature delivery. Irregular menstrual cycles and poor maternal weight gain are common in adolescents.15

Many adolescents who become pregnant may be in denial or may not be aware of the pregnancy as late as the second and third trimesters. Many signs of pregnancy may mimic normal adolescent female changes and behavior due to increased hormonal levels such as:

  • A missed menstrual period (especially females involved in sports).
  • Nausea or vomiting.
  • Intense aversion to foods.
  • Sore nipples or breasts.
  • Unusual fatigue.
  • Frequent urination.
  • Unusual mood swings.

Thus, dental practitioners may be treating patients who are unaware they are pregnant.

It is suggested medical histories taken from females of child bearing age should include questions addressing the possibility of pregnancy:

  • Is there a possibility of pregnancy or are you trying to get pregnant?
  • When was your last period?
  • Have you experienced recent excessive weight gain, increased nausea.16