2 Nonadherence with medical therapy is a complex multi- faceted problem involving patient and family factors, disease factors, physician factors, and regimen factors [11]. Unfor- tunately, none of these factors have been found to reliably predict which patients will or will not take their prescribed medication. Various methods are available to assess adher- ence; however, all have advantages and disadvantages and no universally accepted gold standard exists. The accuracy of self-reporting is often questioned, in particular when the suggestion is that compliance is good. Pill counts may also underestimate adherence as patients “dump” their pills prior to their clinic visit. Measurement of drug levels, available for a limited number of medications, only reﬂects recent inges- tion. Electronic monitors that provide continuous “real- time” measurement can provide information on temporal dosing patterns and allow correlation with breakthrough clinical events. It is important to have a high index of suspicion in order to identify early those noncompliant patients who have failed to attain their treatment goal and who may beneﬁt from more targeted support and adherence-enhancing strategies that may include educational and behavioural approaches. Potential barriers to adherence should be identiﬁed. No single intervention has been shown to be eﬀective across all patients, conditions, and settings [12]. In a review of interventions for enhancing medication adherence less than one-half of the interventions tested were associated with statistically signiﬁcant increases in medication adherence and only 29 of 93 interventions reported statistically signiﬁcant improvements in treatment outcomes. The common theme was more frequent interaction with patients with attention to adherence [13]. 3. Medication Adherence in Pregnancy Despite the ample evidence in the literature of the important role of adherence with drug therapy in inﬂuencing treatment outcome in the general medical population, there is a relative paucity of studies that have focused speciﬁcally on whether pregnant women do or do not take their medication. Much of the research addressing medication compliance during pregnancy has been undertaken in women with HIV infec- tion although there are scattered reports in other medical conditions. The information available suggests that nonadherence with prescribed drugs is also a problem in the pregnant pop- ulation. 39% of women who received one or more prescrip- tions reported noncompliance during pregnancy when inter- viewed within two weeks after delivery. Reasons included doubts about the use of the drug during pregnancy, expected side eﬀects, disappearance of the complaints for which the drugs were prescribed, or the complaint persisted notwith- standing drug therapy. Approximately 40% of women had had one or more questions about drugs during their preg- nancy with safety being the issue that raised most questions [14]. Similarly, using data from the North Jutland Prescription Database and from the Danish National Birth Cohort survey, Obstetrics and Gynecology International the overall compliance rate with prescription drugs in preg- nant women was estimated to be 43% [15]. In the outpatient clinics of an Australian hospital, medication nonadherence was reported by 59.1% of pregnant participants with a chronic health condition. Nonadherence was mainly nonin- tentional, with forgetting to take medication being the most common reason. In this study, the majority of participants had some concerns about using any medication during preg- nancy [16]. 3.1. Adherence with HIV Medications. Poor adherence with HIV treatment regimens may be a determinant of virologic failure, emergence of drug resistant virus, and disease pro- gression [17]. In addition to treating the mother’s underlying disease, antiretroviral treatment in pregnant women also aims to prevent vertical perinatal HIV transmission to the child [18, 19]. Highly active antiretroviral therapy (HAART) has reduced mother-to-child transmission rates to around 1 to 2% in resource-rich countries [20]. Lack of medication adherence in pregnant women with HIV infection may interfere with these goals. Medication nonadherence was a signiﬁcant factor associated with suboptimal viral suppres- sion at the time of delivery (deﬁned by HIV viral load ≥ 1000 copies) in addition to baseline viral load ≥10,000 copies per milliliter [21]. Studies have shown that HIV-infected pregnant women have greater adherence with antiretroviral drugs than non- pregnant women [22–24]. However, adherence rates during pregnancy are still not optimal and have been reported to be between 43.1% and 80% using various methods of compli- ance assessment [22–28]. Better compliance with prescribed medications during pregnancy may be related to concern for the baby’s health [24, 29]. In the Women and Infant Transmission Study, 90% of women who reported improved adherence with their HIV medications during pregnancy stated that their baby’s health was the primary reason [24]. Dosing regimen has also been shown to be important as less than 6 pills per day and up to two doses per day were associated with better adherence [22]. Similarly, pregnant women who were prescribed zidovudine only once or twice daily demonstrated signiﬁcantly higher adherence than those prescribed this medication three to ﬁve times per day [23]. Social support, especially from family members, has a positive inﬂuence on medication-taking behaviour [25]. Barriers to good adherence with antiretroviral therapy include being preoccupied with other issues and hectic life- styles [29] as well as illicit drug use [27, 28]. Untreated de- pression during pregnancy is also associated with nonadher- ence to HIV treatment regimens and treatment of depression may improve medication adherence [30]. As poor adherence with antiretroviral drugs during pregnancy may predict nonattendance at infant followup [31], identifying women who are having trouble taking their medication is important. 3.2. Adherence with Medications Prescribed for Other Condi- tions. As in the general population less than perfect adher- ence with medication taking has been demonstrated in pa- tients with other medical conditions, examples of which will be discussed.