Injection drug use among HIV-infected pregnant women appears to be declining, from 11% during 2000-2003 to 8% during 2005-2008 in U.S. Enhanced Perinatal Surveillance (EPS); use of any illicit drugs declined from 20% to 11% in the same periods [21, 22]. Another US study, the Surveillance Monitoring of ART Toxicities (SMARTT) cohort reported ‘hard drug use’ by 3% of women in 2007-2010 [23], while also reporting positive behavioral screens for mental disorder (mainly post-traumatic stress disorder) or substance abuse in 35% compared to 26% in the general population [24].

Immigrants from lesser-resourced countries account for an increasing proportion of HIV-exposed deliveries, including 78.5% of infected women delivering in the UK during 2000-2009 [15] and 60% in Canada during 2007-2009 [25]. Among mothers of HIV-infected infants reported to US National HIV Surveillance during 2003-2007, 21% were born in countries other than the US [26]. The annual percentage of HIV-infected pregnant women born in Africa and delivering was 24-78% in several western European countries during the past decade [7, 12, 27, 28]. Immigrant women were at some risk of less frequent uptake of PMTCT interventions, specifically, accessing prenatal care and ARV initiation [27, 29].

An estimated 140,000 HIV-serodiscordant heterosexual couples reside in the US [30], but whether that number or its proportion of HIV-infected persons is changing is unknown. It is known that many HIV-infected women have HIV-uninfected partners. Of 181 HIV-infected US women of childbearing age, 62% had negative partners and 11% had partners of unknown status [31]. In France, among HIV-infected individuals, 41.5% of men and 43.6% of women had partners of unknown or negative status [32]. The patterns of serodiscordance offer different opportunities for prevention of HIV MCT, which become more relevant as the population's desire to conceive and bear children increases. One US study of 181 women of childbearing age reported that 59% desired children, of whom 66% intend to have children [31]. Studies from Canada and the UK have reported similar findings [33, 34]. Of HIV-infected persons in France, 20% of men and 33% of women expected to have children [32]. Finally, a study of perinatally infected females of childbearing age found that 70% intended to have children [35]. Safer conception for HIV-discordant couples is being made possible through the use of assisted reproductive technology [30, 36]—e.g., artificial insemination of an HIV positive woman, or so-called ‘sperm washing’, with intrauterine insemination or in vitro fertilization—and antiretrovirals for pre-exposure prophylaxis [37] or treatment as prevention [38]. It remains to be seen whether these approaches will lead to an increase in the annual number of HIV-exposed infants.

The annual number of HIV-infected infants born in the US and most other high-income countries is decreasing. Though the numbers of deliveries by HIV-infected pregnant women appears to be increasing, at least in the US, this trend is not the result of increasing incidence among women, as HIV incidence is actually decreasing [54]. The increased number of deliveries appears to be the result of improved survival and overall well-being, accompanied by increasing desire to conceive and increasing numbers of women with ‘repeat’ pregnancies. Whether the number of HIV-exposed pregnancies will further increase as the availability of assisted reproductive technologies increases—and how such technologies will change PMTCT—remains to be seen. The evident connection between survival and ART means that increasing numbers of women will be ART-experienced when they conceive. It can be anticipated that recent ART guidelines, which recommend treatment for all HIV-infected persons [55], when implemented, will constitute an important structural intervention for EMCT, leading to an increasing proportion with viral suppression among women of childbearing age. This experience leads not only to increased prenatal ARV exposure, but also the possibility of an increasing prevalence of ARV-resistant HIV, which in turn could result in more women being on second- and third-line regimens whose effectiveness may differ So far, MTCT does not appear to be substantially affected by ARV-resistance [42]. Additional antiviral exposure—as well as additional maternal morbidity--in this population may occur as a result of maternal co-infection with other viruses, notably hepatitis B and hepatitis C viruses. Though immigrant HIV-infected women of childbearing age comprise an increasing percentage in many resource-rich countries, their PMTCT problems relate more to health care access and utilization (e.g., timely diagnosis, linkage to and retention in primary and prenatal care) than to biomedical issues (e.g., resistant virus, adherence).

In the US, most of the ongoing mother-to-childtransmissions are apparently attributable to incomplete uptake of elements of the Perinatal Prevention Cascade, e.g., identification of HIV-infected women and effective retention of them in care [56]. It is likely that many of such transmissions are from women who are extremely difficult to reach, for reasons in addition to illicit drug abuse, reasons which include the substantial degree of poverty [57] and mental health problems in the population. The expansion in medical care access in the U.S. anticipated from the Affordable Care Act may mitigate some of poverty's effects, but it can be predicted that the social instability and segregation associated with poverty will continue to aggravate problems of access. Indeed, in this era of low MCT rates, as each transmission's specific characteristics take on heightened importance, it remains important to review cases, with the goal of changing the local system in ways that may prevent further transmissions and improve the care of HIV-infected women to optimize their health prior to—and between—pregnancies, as well as to prevent unwanted pregnancies. The Framework for EMCT [1] incorporates Case Review and Community Action as one of its key components, as the Fetal-Infant Mortality Review—HIV (FIMR-HIV) Prevention Program. The US Centers for Disease Control and Prevention includes FIMR-HIV among activities encouraged by its prevention grantees. These reviews have identified issues of domestic violence and maternal mental health diagnoses [58]. FIMR-HIV has also recognized the dramatic effect on women—including depression and decreased linkage to care and medication adherence—when they lose custody of children after birth.

It will remain a challenge for public health institutions to commit new funds to PMTCT as the numbers of perinatal cases decline in contrast to the number of adult cases and when comparing resource-rich to resource-poor settings. Actionable data on the number of HIV-infected women delivering, and on the kind of care they receive, is essential for public health authorities to monitor EMCT adequately. Support for this can come from state laws and policies which advocate “opt-out” HIV testing and encourage perinatal HIV exposure reporting. Medical care providers must be made aware of changes in these policies. Vital to all of these considerations, however, is the recognition that “elimination” of mother-to-child transmission is not a single event, but, rather, is an ongoing process. That process necessarily must address the needs of successive annual waves of HIV-infected pregnant women as long as there are new cases of HIV in women, underscoring the importance of primary prevention and appropriate HIV care for women.