Physiology and Complications

To define rational management guidelines, a review of the normal processes of pregnancy and fetal development is provided here.

Endocrine changes are the most significant basic alterations that occur with pregnancy. They result from the increased production of maternal and placental hormones and from modified activity of target end organs.

Fatigue is a common physiologic finding during the first trimester that may have a psychologic impact. A tendency toward syncope and postural hypotension also has been noted. During the second trimester, patients typically have a sense of well-being and relatively few symptoms. During the third trimester, increasing fatigue and discomfort and mild depression may be reported. Several cardiovascular changes occur as well. Blood volume increases by 40% to 50%, cardiac output by 30% to 50%, but red blood cell volume increases by only about 15% to 20%, resulting in a fall in the maternal hematocrit.< ?xml:namespace prefix = "mbp" />¹ Despite the increase in cardiac output, blood pressure falls (usually to 100/70 mm Hg or lower) during the second trimester, and a modest increase is noted in the last month of pregnancy. This increase in blood volume is associated with high flow–low resistance circulation, tachycardia, and heart murmurs, and it may unmask glomerulopathies, peripartum cardiomyopathy, arterial aneurysms, or arteriovenous malformations. A benign systolic ejection murmur is a rather common finding occurring in more than 90% of pregnant women, which disappears shortly after delivery.¹ A murmur of this type is considered physiologic or functional. However, a murmur that preceded pregnancy or persisted after delivery would require further evaluation for determination of its significance.

During late pregnancy, a phenomenon known as supine hypotensive syndrome may occur that manifests as an abrupt fall in blood pressure, bradycardia, sweating, nausea, weakness, and air hunger when the patient is in a supine position.^1,2 Symptoms and signs are caused by impaired venous return to the heart resulting from compression of the inferior vena cava by the gravid uterus. This leads to decreased blood pressure, reduced cardiac output, and impairment or loss of consciousness. The remedy for the problem is for the patient to roll over onto her left side, which lifts the uterus off the vena cava. Blood pressure should rapidly return to normal.

Blood changes in pregnancy include anemia and a decreased hematocrit value. Anemia occurs because blood volume increases more rapidly than red blood cell mass. As a result, a fall in hemoglobin and a marked need for additional folate and iron occur. A majority of pregnant women have insufficient iron stores—a problem that is exaggerated by significant blood loss. However, there is disagreement over whether or not to routinely provide iron supplementation.¹ Although changes in platelets are usually clinically insignificant, most studies show a mild decrease in platelets during pregnancy.³ Several blood clotting factors, especially fibrinogen and factors VII, VIII, IX, and X, are increased. As a result of the increase in many of the coagulation factors, combined with venous stasis, pregnancy is associated with a hypercoagulable state. Interestingly, however, the prothrombin time, activated partial thromboplastin time, and thrombin time all fall slightly but remain within the limits of normal nonpregnant values.¹ The overall risk of thromboembolism in pregnancy is estimated to be 1 in 1500 and accounts for 25% of maternal deaths in the United States.⁴

Several white blood cell (WBC) and immunologic changes occur. The WBC count increases progressively throughout pregnancy, primarily because of an increase in neutrophils, and is nearly doubled by term. The reason for the increase is unclear but may involve elevated estrogen and cortisol levels.⁵ This increase in neutrophils may complicate the interpretation of the complete blood count during infection. Also, during pregnancy, the immune system shifts from helper T cell type 1 (T_H1) dominance to T_H2 dominance. This shift leads to immune suppression. Clinically, the decrease in cellular immunity leads to increased susceptibility to intracellular pathogens such as cytomegalovirus virus, herpes simplex virus, varicella virus, and the agent of malaria.¹ The decrease in cellular immunity may explain why rheumatoid arthritis frequently improves during gestation, since it is a cell-mediated immunopathologic disease.⁶ During the postpartum period, rebound and heightened inflammatory activity occurs.

Changes in respiratory function during pregnancy include elevation of the diaphragm which decreases the volume of the lungs in the resting state, thereby reducing total lung capacity by 5% and the functional residual capacity (FRC), the volume of air in the lungs at the end of quiet exhalation, by 20%.⁷ Of interest, the respiratory rate and vital capacity remain unchanged. These ventilatory changes produce an increased rate of respiration (tachypnea) and dyspnea that is worsened by the supine position. Thus, it is not surprising that sleep during pregnancy is impaired, especially during the third trimester.⁸

Pregnancy predisposes the expectant mother to an increased appetite and often a craving for unusual foods. As a result, the diet may be unbalanced, high in sugars, or nonnutritious. This can adversely affect the mother’s dentition and also contribute to significant weight gain. Taste alterations and an increased gag response are common as well. The pH and production of saliva are probably unchanged.⁹ No evidence exists that pregnancy causes or accelerates the course of dental caries. Nausea and vomiting, or “morning sickness,” may complicate up to 70% of pregnancies. Typical onset is between 4 and 8 weeks of gestation, with improvement before 16 weeks; however, 10% to 25% of women still experience symptoms at 20 to 22 weeks of gestation, and some women experience this throughout the pregnancy.¹⁰ The cause is not well understood. Some patients may experience extreme nausea and frequent vomiting, which can be a cause of dental erosion.

The general pattern of fetal development should be understood when dental management plans are being formulated. Normal pregnancy lasts approximately 40 weeks. During the first trimester, organs and systems are formed (organogenesis). Thus, the fetus is most susceptible to malformation during this period. After the first trimester, the major aspects of formation are complete, and the remainder of fetal development is devoted primarily to growth and maturation. Thus, the chances of malformation are markedly diminished after the first trimester. A notable exception to this relative protection is the fetal dentition, which is susceptible to malformation from toxins or radiation, and to tooth discoloration caused by administration of tetracycline.

Complications of pregnancy are infrequent when appropriate prenatal care is provided and the mother is healthy. Unfortunately, complications occur more often in expectant mothers who harbor pathogens (oral and extraoral) and smoke, and in nonwhites than in whites in the United States.¹¹ Common complications include infection, enhanced inflammatory response, glucose abnormalities, and hypertension.¹² Each of these entities increases the risks for preterm delivery, perinatal mortality, and congenital anomalies. Insulin resistance is a contributing factor to the development of gestational diabetes mellitus (GDM), which occurs in 2% to 6% of pregnant women. GDM increases the risks for infection and large birth weight babies. Hypertension is of particular interest because it can lead to end organ damage or preeclampsia, a clinical condition of pregnancy that manifests as hypertension, proteinuria, edema, and blurred vision. Preeclampsia, defined as hypertension with proteinuria, progresses to eclampsia if seizures or coma develop. The cause of eclampsia is unknown but appears to involve sympathetic overactivity associated with insulin resistance, the renin-angiotensin system, lipid peroxidation, and inflammatory mediators.¹³ Complications of pregnancy that are unresponsive to diet modification and palliative care ultimately require drugs or hospitalization for adequate control.

Another consideration related to fetal growth is spontaneous abortion (miscarriage). Spontaneous abortion is the natural termination of pregnancy before the 20th week of gestation, and occurs in approximately 15% of all pregnancies.¹⁴ The most common causes of spontaneous abortion are morphologic or chromosomal abnormalities which prevent successful implantation. It is most unlikely that any dental procedure would be implicated in spontaneous abortion, provided fetal hypoxia and exposure of the fetus to teratogens are avoided. Febrile illness and sepsis also can precipitate a miscarriage; therefore, prompt treatment of odontogenic infection and periodontitis is advised.

Because of immature liver and enzyme systems, the fetus has a limited ability to metabolize drugs. Pharmacologic challenge of the fetus is to be avoided when possible.

During the postpartum period, the mother may suffer from lack of sleep and postpartum depression. Also during the postpartum period, risks for the occurrence of autoimmune disease, particularly rheumatoid arthritis, multiple sclerosis, and thyroiditis, are increased.

Medical Considerations

Management recommendations during pregnancy should be viewed as general guidelines—not as definitive rules. The dentist should assess the general health of the patient through a thorough medical history. Information to ascertain includes current physician, medications taken, use of tobacco, alcohol, or illicit drugs, history of gestational diabetes, miscarriage, hypertension, and morning sickness. If the need arises, the patient’s obstetrician should be consulted. Of interest, in a 1992 survey of obstetricians,¹⁵ 91% of respondents indicated that they preferred not to be contacted in regard to “routine” dental care. However, 88% wanted to be consulted before the dentist prescribed antibiotics, and 54% wanted to participate in a consultation before the dentist prescribed analgesics (Box 17-1).

Pregnancy is a special event in a woman’s life; hence, it is an emotionally charged experience. Establishing a good patient-dentist relationship that encourages openness, honesty, and trust is an integral part of successful management. This kind of relationship greatly reduces stress and anxiety for both patient and dentist.

As with all patients, measuring vital signs is important for identifying undiagnosed abnormalities and the need for corrective action. At a minimum, blood pressure and pulse should be measured. Systolic pressure at or above 140 mm Hg and diastolic pressure at or above 90 mm Hg are signs of hypertension (see Chapter 3). Also, clinical concern is appropriate if the patient’s blood pressure increases 30 mm Hg or more in systolic or increases 15 mm Hg in diastolic blood pressure over prepregnancy values, because these changes can be a sign of preeclampsia.¹⁶ Confirmed hypertensive values dictate that the patient be referred to a physician to ensure that preeclampsia and other cardiovascular disorders are properly diagnosed and managed.

Treatment Timing

Other than as part of a good plaque control program, elective dental care is best avoided during the first trimester because of the potential vulnerability of the fetus (Table 17-1). The second trimester is the safest period during which to provide routine dental care. Emphasis should be placed on controlling active disease and eliminating potential problems that could occur later in pregnancy or during the immediate postpartum period, because providing dental care during these periods often is difficult. Extensive reconstruction or significant surgical procedures are best postponed until after delivery.

TABLE 17-1 Treatment Timing During Pregnancy*