Almost all women will experience pain during pregnancy. Common musculoskeletal conditions can cause severe pain in an otherwise uncomplicated pregnancy. Some women will enter pregnancy with preexisting painful disorders, and management of the ongoing pain and painful exacerbations can be challenging. This chapter reviews the common painful musculoskeletal conditions of pregnancy and an approach to the management of chronic pain during pregnancy and in breastfeeding mothers.
Use of Medications During Pregnancy
Medical management of pregnant patients should begin with attempts to minimize the use of all medications and use nonpharmacologic therapies whenever possible. When opting for drug therapy, the clinician must consider any potential for harm to the mother, the fetus, and the course of the pregnancy. The degree of protein binding and lipid solubility of the medication, the speed of maternal metabolism, and molecular weight all affect placental transfer of medications from mother to fetus. With the exception of large polar molecules (such as heparin and insulin), as well as ionized molecules (glycopyrrolate), almost all medications will reach the fetus to some degree.
Approximately 3% of newborns will have a significant congenital malformation. Only 25% of fetal malformations have a known genetic cause, and just 2% to 3% have a clear environmental link, such as maternal medication exposure during organogenesis. One of the major limitations in evaluating any medication’s potential for causing harm to a developing human fetus is the degree of species specificity for congenital defects. A classic example of such specificity is the drug thalidomide; nonprimate studies revealed no teratogenic effects, but severe limb deformities occurred in human offspring when thalidomide was prescribed during pregnancy.
The most critical period for minimizing maternal drug exposure is during early development, from conception through the 10th menstrual week of pregnancy (the 10th week following the start of the last menstrual cycle). Drug exposure before organogenesis (prior to the fourth menstrual week) usually causes an all-or-none effect—the embryo either does not survive or develops without abnormalities. Drug effects later in pregnancy typically lead to single- or multiple-organ involvement, developmental syndromes, or intrauterine growth retardation. Certain medications may not influence fetal organ development directly but have the potential to influence the physiology of pregnancy adversely. For example, nonsteroidal anti-inflammatory drugs (NSAIDs) may delay the onset of labor, decrease amniotic fluid volume, or place a newborn at risk for pulmonary hypertension or renal injury.
The U.S. Food and Drug Administration (FDA) has developed a five-category labeling system for all approved drugs in the United States ( Table 35.1 ). This labeling system rates the potential risk for teratogenic or embryotoxic effects based on available scientific and clinical evidence. It is important to note that the FDA classification system has been revised to address neonatal influences other than teratogenicity. For example, ibuprofen is associated with decreased amniotic fluid and constriction of the ductus arteriosus. In fact, many NSAIDs used to be class B before 30 weeks and class D after 30 weeks. More recently, this has changed to class C before 30 weeks and class D thereafter. Because few medications have undergone large-scale testing during human pregnancy, most are category C, which indicates incomplete knowledge of the potential for benefit and harm with drug therapy. More specifically, our present knowledge about the adverse effects of uncontrolled pain, as well as the risks associated with administering medications during pregnancy, remains incomplete, and the physician is left to weigh the risks against the benefits of instituting pharmacologic therapy for each individual.
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