During pregnancy, the increased metabolic demands of both the mother and the fetus are accompanied by a 40% increase in blood volume, a 30% to 40% increase in cardiac output, and a 15% to 20% increase in erythrocytes [5]. The production of erythrocytes, with their oxygen-binding hemoglobin complex, is not proportionate to the increased blood volume. Therefore, the hematocrit, defined as the proportion by volume of blood comprised of erythrocytes, decreases. A proportionate decrease in the iron-containing hemoglobin complex can lead to anemia.

The increased blood flow across the aortic and pulmonary valves causes the development of a benign systolic murmur in approximately 90% of pregnant patients; this generally resolves after the pregnancy [6]. An increase in clotting factors (such as fibrinogen) and a decrease in anticlotting factors can place the pregnant patient at an increased risk of a thromboembolic event [7]. There is also a risk for hypotension during pregnancy, particularly in the last trimester.

The sustained increase in progesterone levels during pregnancy decreases the tone of the lower esophageal region and affects gastric and intestinal motility [9]. The gag reflex can be exacerbated during pregnancy, which is problematic during dental procedures in which aerosols are generated. The progressive increase in fetal size causes an increase in intragastric pressure and can lead to the development of acid reflux. Protracted acid reflux can be deleterious to the enamel of the lingual surfaces of the teeth and result in its progressive erosion. Patients who experience excessive vomiting (hyperemesis gravidarum) and/or acid reflux during pregnancy may be instructed to rinse with a solution of one teaspoon of baking soda to one cup of water to neutralize the highly acidic gastric contents [10]. Tooth brushing should be deferred until all of the acidic residue can be removed from the teeth (i.e., wait 60 minutes after rinsing before brushing) [11].

The abrasiveness of toothpaste coupled with acid-laden enamel can accelerate the demineralization process and loss of enamel. Acidic residue that remains on the teeth after repeated incidents of acid reflux can lead to enamel demineralization, exposure of the underlying dentin, increased tooth sensitivity to thermal stimuli and sweets, and an increased risk of caries. Sensitive teeth are usually avoided during brushing and flossing, which can further increase the risk of caries and periodontal problems. Some patients will develop cravings for foods that are sugar-laden and deleterious to oral health and overall health. These patients should be counseled to monitor their diet and to maintain meticulous oral hygiene throughout their pregnancy, with a reminder that tooth brushing should be avoided for 60 minutes after eating highly acidic or sugary foods [11].

The most frequent oral complication to develop in pregnancy is pregnancy gingivitis, occurring in 60% to 75% of pregnant patients [9,12]. During pregnancy, the gingival tissues may exhibit an increased inflammatory response to local irritants, such as plaque and calculus, due to the altered levels of estrogen and progesterone. Research indicates that there are significant changes in the oral flora during pregnancy, with a shift to more anaerobic flora as the pregnancy progresses and an increase in the presence of Prevotella intermedia[13]. Pregnancy gingivitis begins at the marginal gingiva and extends into the interdental papilla and may involve a few teeth or the entire dentition. In general, the condition has an onset during the first trimester of pregnancy and may increase significantly throughout pregnancy [14].

Some pregnant women still believe the widely circulated myth that pregnancy and tooth loss have a direct relationship. The adage of "a tooth loss for every pregnancy," attributed to calcium being withdrawn from the teeth to supply the calcium needs of the developing fetus, is false. Dental calcium is in a stable crystalline configuration and is not subject to withdrawal to meet the calcium demands of the mother or the fetus. Calcium metabolism is controlled by parathyroid hormone (PTH) and calcitonin. When a calcium deficit exists, PTH triggers the release of calcium stored in bones, not teeth, to obtain the required amount of calcium. Calcitonin hastens the uptake of calcium into bones when a surplus of calcium exists.

Pyogenic granulomas are a pathologic entity that can occur in many patients. However, when they occur during pregnancy, they are referred to as "pregnancy tumors" [18]. These benign granulomas are a locally progressive manifestation of pregnancy gingivitis that occur in up to 5% of all pregnancies, most often during the second or third trimester [18,19]. The lesions have a highly developed vascular network secondary to the hormonal changes in pregnancy. They are typically painless but can bleed easily during brushing, flossing, or eating. Pyogenic granulomas in pregnancy usually develop from the interdental papillae on the buccal or labial surfaces of the teeth. Smaller lesions will usually regress after childbirth, but larger lesions may require surgical excision for their elimination. The rich vascular network associated with these lesions can cause profuse bleeding upon their removal. Clinicians should only undertake the surgical excision of these lesions if they are capable of achieving hemostasis after the procedure.

Aside from adversely affecting the quality of life, xerostomia can compromise oral health. Decreased salivary flow results in less self-cleansing action for the teeth and a decrease in immunoglobulins. An increased retention of plaque can lead to an increased risk of caries and periodontal problems. The decreased lubricating medium of saliva can lead to increased oral discomfort for women who use partial or complete dentures. Eating can become difficult for these patients at a time when appropriate maternal and fetal nutrition are essential. Fungal organisms such as Candida albicans can flourish in a xerostomic environment and cause candidiasis.

Acetaminophen was previously listed as a category B or C drug [23]. As with other medications, the lowest dose and duration should be used. Ibuprofen and naproxen previously were considered category B for the first and second trimesters, but both were considered category D in the third trimester [23]. This change is due to an increased risk for closure of the fetal ductus arteriosus, fetal renal damage, inhibited clotting, and delayed labor and birth [23]. Opioid narcotic use in the third trimester should be avoided as it can cause neonatal respiratory depression [25].

Acetaminophen was previously listed as a category B or C drug [23]. As with other medications, the lowest dose and duration should be used. Ibuprofen and naproxen previously were considered category B for the first and second trimesters, but both were considered category D in the third trimester [23]. This change is due to an increased risk for closure of the fetal ductus arteriosus, fetal renal damage, inhibited clotting, and delayed labor and birth [23]. Opioid narcotic use in the third trimester should be avoided as it can cause neonatal respiratory depression [25].

Tetracycline and its derivatives were considered pregnancy category D and, as a class, their use should be avoided during pregnancy [23]. These medications bind to hydroxyapatite within the developing tooth and cause brown discoloration of the teeth, poorly formed enamel, and problems with bone growth [23,27].

If dental treatment is performed during pregnancy, the second trimester is generally the safest in terms of both maternal and fetal concerns. Fetal organ development is completed by the end of the first trimester, and morning sickness symptoms often begin to subside. During the third trimester, increasing uterine weight can cause discomfort when the patient is placed in a supine position typical for most dental procedures. Emergency situations such as acute infections, fractured teeth, endodontic problems, or traumatic injuries may require a diversion from this ideal timing.