AETC National Resource Center


	participating institutions: Johns Hopkins University AIDS Service, New York State DOH AIDS Institute, The CORE Center, Cook County Hospital

ART & PREGNANCY

last updated: May 4, 2001

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Background

Considerations Regarding the Use of Antiretroviral Drugs by HIV-1-Infected Pregnant Women and Their Infants
Treatment recommendations for pregnant women infected with HIV-1 have been based on the belief that therapies of known benefit to women should not be withheld during pregnancy unless they could adversely affect the mother, fetus, or infant and unless these adverse effects outweigh the benefit to the woman (17). Combination antiretroviral therapy, generally consisting of two nucleoside analogue reverse tran-scriptase inhibitors and a protease inhibitor, is the currently recommended standard treatment for HIV-1-infected adults who are not pregnant (14) (See the "Guidelines for the Use of Antiretroviral Agents in HIV-Infected Adults and Adolescents".) Pregnancy should not preclude the use of optimal therapeutic regimens. However, recommendations regarding the choice of antiretroviral drugs for treatment of infected pregnant women are subject to unique considerations, including a) potential changes in dosing requirements resulting from physiologic changes associated with pregnancy, b) potential effects of antiretroviral drugs on the pregnant woman, and c) the potential short- and long-term effects of the antiretroviral drug on the fetus and new-born, which may not be known for many antiretroviral drugs. The decision to use any antiretroviral drug during pregnancy should be made by the woman after discussing the known and unknown benefits and risks to her and her fetus with her healthcare provider.

Physiologic changes that occur during pregnancy may affect the kinetics of drug absorption, distribution, biotransformation, and elimination, thereby affecting requirements for drug dosing and potentially altering the susceptibility of the pregnant woman to drug toxicity. During pregnancy, gastrointestinal transit time becomes prolonged; body water and fat increase throughout gestation and are accompanied by increases in cardiac output, ventilation, and liver and renal blood flow; plasma protein concentrations decrease; renal sodium reabsorption increases; and changes occur in metabolic enzyme pathways in the liver. Placental transport of drugs, compartmentalization of drugs in the embryo/fetus and placenta, biotransformation of drugs by the fetus and placenta, and elimination of drugs by the fetus also can affect drug pharmacokinetics in the pregnant woman. Additional considerations regarding drug use in pregnancy are a) the effects of the drug on the fetus and newborn, including the potential for teratogenicity, mutagenicity, or carcinogenicity and b) the pharmacokinetics and toxicity of transplacentally transferred drugs. The potential harm to the fetus from maternal ingestion of a specific drug depends not only on the drug itself, but on the dose ingested, the gestational age at exposure, the duration of exposure, the interac-tion with other agents to which the fetus is exposed, and, to an unknown extent, the genetic makeup of the mother and fetus.

Information about the safety of drugs in pregnancy is derived from animal toxicity data, anecdotal experience, registry data, and clinical trials. Minimal data are available regarding the pharmacokinetics and safety of antiretrovirals other than ZDV during pregnancy. In the absence of data, drug choice should be individualized and must be based on discussion with the woman and available data from preclinical and clinical testing of the individual drugs.

Preclinical data include in vitro and animal in vivo screening tests for carcinogenicity, clastogenicity/mutagenicity, and reproductive and teratogenic effects. However, the predictive value of such tests for adverse effects in humans is unknown. For example, of approximately 1,200 known animal teratogens, only about 30 are known to be teratogenic in humans (18). In addition to antiretroviral agents, many drugs commonly used to treat HIV-1-related illnesses may have positive findings on one or more of these screening tests. For example, acyclovir is positive on some in vitro carcinogenicity and clastogenicity assays and is associated with some fetal abnormalities in rats; however, data collected on the basis of human experience from the Acyclovir in Pregnancy Registry have indicated no increased risk for birth defects in infants with in utero exposure to acyclovir (19). Limited data exist regarding placental passage and long-term animal carcinogenicity for the FDA-approved antiretroviral drugs (Table 2).

**SEE SAFETY AND TOXICITY OF INDIVIDUAL ANTIRETROVIRAL DRUGS IN PREGNANCY TO OBTAIN IMPORTANT AND DETAILED INFORMATION**

Combination Antiretroviral Therapy and Pregnancy Outcome
There are limited data concerning combination antiretroviral therapy in pregnancy. A retrospective Swiss report evaluated the pregnancy outcome in 37 HIV-infected pregnant women treated with combination therapy; all received two reverse transcriptase inhibitors and 16 received one or two protease inhibitors (20). Almost 80 percent of women developed one or more typical adverse effects of the drugs such as anemia, nausea/vomiting, aminotransferase elevation, or hyperglycemia. A possible association of combination antiretroviral therapy with preterm births was noted, as 10 of 30 babies were born prematurely. The preterm birth rate did not differ between women receiving combination therapy with or without protease inhibitors. The contribution of maternal HIV disease stage and other covariates that might be associated with a risk for prematurity were not assessed. Furthermore, some studies have shown elevated preterm birth rates in HIV-infected women who have not received any antiretroviral therapy (21-23). To evaluate the baseline rates of adverse pregnancy outcome and risk factors for such outcomes in HIV-infected pregnant women, a meta-analysis of multiple PACTG perinatal trials and cohort studies is in progress. Preliminary analyses do not indicate an elevated risk of preterm delivery among infants born to women receiving combination antiretroviral therapy with or without protease inhibitors compared to those receiving single drug or no antiretroviral therapy. Until more information is known, it is recommended that HIV-infected pregnant women who are receiving combination therapy for treatment of their HIV infection should continue their provider-recommended regimen. They should receive careful, regular monitoring for pregnancy complications and for potential toxicities.

Protease Inhibitor Therapy and Hyperglycemia
Hyperglycemia, new onset diabetes mellitus, exacerbation of existing diabetes mellitus, and diabetic ketoacidosis have been reported with administration of protease inhibitor antiretroviral drugs in HIV-infected patients (24-27). In addition, pregnancy is itself a risk factor for hyperglycemia; it is unknown if the use of protease inhibitors will exacerbate the risk for pregnancy-associated hyperglycemia. Clinicians caring for HIV-infected pregnant women who are receiving protease inhibitor therapy should be aware of the risk of this complication, and closely monitor glucose levels. Symptoms of hyperglycemia should be discussed with pregnant women who are receiving protease inhibitors.

Mitochondrial Toxicity and Nucleoside Analogue Drugs
Nucleoside analogue drugs are known to induce mitochondrial dysfunction, as the drugs have varying affinity for mitochondrial gamma DNA polymerase. This affinity can result in interference with mitochondrial replication, resulting in mitochondrial DNA depletion and dysfunction (28). The relative potency of the nucleosides in inhibiting mitochondrial gamma DNA polymerase in vitrois highest for zalcitabine (ddC), followed by didanosine (ddI), stavudine (d4T), lamivudine (3TC), ZDV and abacavir (ABC) (29). Toxicity related to mitochondrial dysfunction has been reported in infected patients receiving long-term treatment with nucleoside analogues, and generally has resolved with discontinuation of the drug or drugs; a possible genetic susceptibility to these toxicities has been suggested (28). These toxicities may be of particular concern for pregnant women and infants with in utero exposure to nucleoside analogue drugs.

Issues in Pregnancy

Clinical disorders linked to mitochondrial toxicity include neuropathy, myopathy, cardiomyopathy, pancreatitis, hepatic steatosis, and lactic acidosis. Among these disorders, symptomatic lactic acidosis and hepatic steatosis may have a female preponderance (30). These syndromes have similarities to the rare but life-threatening syndromes of acute fatty liver of pregnancy and hemolysis, elevated liver enzymes and low platelets (the HELLP syndrome) that occur during the third trimester of pregnancy. A number of investigators have correlated these pregnancy-related disorders with a recessively-inherited mitochondrial abnormality in the fetus/infant that results in an inability to oxidize fatty acids (31-33). Since the mother would be a heterozygotic carrier of the abnormal gene, there may be an increased risk of liver toxicity due to an inability to properly oxidize both maternal and accumulating fetal fatty acids (34). Additionally, animal studies show that in late gestation pregnant mice have significant reductions (25%-50%) in mitochondrial fatty acid oxidation and that exogeneously administered estradiol and progesterone can reproduce these effects (35, 36); whether this can be translated to humans is unknown. However, these data suggest that a disorder of mitochondrial fatty acid oxidation in the mother or her fetus during late pregnancy may play a role in the etiology of acute fatty liver of pregnancy and HELLP syndrome, and possibly contribute to susceptibility to antiretroviral-associated mitochondrial toxicity.

Lactic acidosis with microvacuolar hepatic steatosis is a toxicity related to nucleoside analogue drugs that is thought to be related to mitochondrial toxicity; it has been reported in infected individuals treated with nucleoside analogue drugs for long periods of time (>6 months). Initially, most cases were associated with ZDV, but subsequently other nucleoside analogue drugs have been associated with the syndrome, particularly d4T. In a report from the FDA Spontaneous Adverse Event Program of 106 individuals with this syndrome (60 patients receiving combination and 46 receiving single nucleoside analogue therapy), typical initial symptoms included 1 to 6 weeks of nausea, vomiting, abdominal pain, dyspnea, and weakness (30). Metabolic acidosis with elevated serum lactate and elevated hepatic enzymes was common. Patients in this report were predominantly female gender and high body weight. The incidence of this syndrome may be increasing, possibly due to increased use of combination nucleoside analogue therapy or increased recognition of the syndrome. In a cohort of infected patients receiving nucleoside analogue therapy followed at Johns Hopkins University between 1989-1994, the incidence of the hepatic steatosis syndrome was 0.13% per year (37). However, in a report from a cohort of 964 HIV-infected individuals followed in France between 1997-1999 the incidence of symptomatic hyperlactatemia was 0.8% per year for all patients and 1.2% for patients receiving a regimen including d4T (38).

The frequency of this syndrome in pregnant HIV-infected women receiving nucleoside analogue treatment is unknown. In 1999, Italian researchers reported a case of severe lactic acidosis in an infected pregnant woman who was receiving d4T/3TC at the time of conception and throughout pregnancy who presented with symptoms and fetal demise at 38 weeks gestation (39). Bristol-Myers Squibb has reported 3 maternal deaths due to lactic acidosis, 2 with and 1 without accompanying pancreatitis, in women who were either pregnant or postpartum and whose antepartum therapy during pregnancy included d4T and ddI in combination with other antiretroviral agents (either a protease inhibitor or nevirapine) (40). All cases were in women who were receiving treatment with these agents at the time of conception and continued for the duration of pregnancy; all presented late in gestation with symptomatic disease that progressed to death in the immediate postpartum period. Two cases were also associated with fetal demise.

It is unclear if pregnancy augments the incidence of the lactic acidosis/hepatic steatosis syndrome reported in non-pregnant individuals receiving nucleoside analogue treatment. However, because pregnancy itself can mimic some of the early symptoms of the lactic acidosis/hepatic steatosis syndrome or be associated with other significant disorders of liver metabolism, these cases emphasize the need for physicians caring for HIV-infected pregnant women receiving nucleoside analogue drugs to be alert for early diagnosis of this syndrome. Pregnant women receiving nucleoside analogue drugs should have hepatic enzymes and electrolytes assessed more frequently during the last trimester of pregnancy and any new symptoms should be evaluated thoroughly. Additionally, because of the reports of several cases of maternal mortality secondary to lactic acidosis with prolonged use of the combination of d4T and ddI by HIV-infected pregnant women, clinicians should prescribe this antiretroviral combination during pregnancy with caution and generally only when other nucleoside analogue drug combinations have failed or caused unacceptable toxicity or side effects.

Issues with in utero exposure

A French group reported 8 cases of uninfected infants with in utero and/or neonatal exposure to either ZDV/3TC (4 infants) or ZDV alone (4 infants) who developed indications of mitochondrial dysfunction after the first few months of life (41). Two of these infants developed severe neurologic disease and died (both of whom had been exposed to ZDV/3TC), three had mild to moderate symptoms, and three had no symptoms but had transient laboratory abnormalities. It is important to note that an association between these findings and in utero exposure to antiretroviral drugs has not been established.

In infants followed through age 18 months in PACTG 076, the occurrence of neurologic events was rare seizures occurred in one child exposed to ZDV and 2 exposed to placebo, and one child in each group had reported spasticity; mortality at 18 months was 1.4% in ZDV-exposed compared to 3.5% in placebo infants (42). In a large database that included 233 deaths in over 20,000 children with and without antiretroviral drug exposure who were born to HIV-infected women followed prospectively in several large cohorts in the United States, no deaths similar to those reported from France were identified (43). However, most of the infants with antiretroviral exposure had been exposed to ZDV alone and only a relatively small proportion (approximately 6%) had been exposed to ZDV/3TC. Evaluation is ongoing to determine if there is any evidence of mitochondrial dysfunction among any of the living children in these cohorts. Data have been reviewed relating to neurologic adverse events in 1,798 children that participated in PETRA, an African perinatal trial that compared 3 regimens of ZDV/3TC (before, during and 1 week postpartum; during labor and postpartum; and during labor only) to placebo for prevention of transmission. No increased risk of neurologic events was observed among children treated with ZDV/3TC compared to placebo, regardless of the intensity of treatment (44). Echocardiograms were prospectively performed every 4 to 6 months during the first 5 years of life in 382 uninfected infants born to HIV-infected women; 9% of infants had been exposed to ZDV prenatally (45). No significant differences in ventricular function were observed between infants exposed and unexposed to ZDV.

If the association of mitochondrial dysfunction and in utero antiretroviral exposures proves to be real, the development of severe or fatal mitochondrial disease in these infants appears to be extremely rare, and should be compared to the clear benefit of ZDV in reducing transmission of a fatal infection by nearly 70% (46). These data emphasize the importance of the existing Public Health Service recommendation for long-term follow-up for any child with in utero exposure to antiretroviral drugs.

Antiretroviral Pregnancy Registry
It is strongly recommended that health care providers who are treating HIV-1-infected pregnant women and their newborns report cases of prenatal exposure to antiretroviral drugs (either alone or in combination) to the Antiretroviral Pregnancy Registry. The Antiretroviral Pregnancy Registry is an epidemiological project to collect observational, nonexperimental data on antiretroviral exposure during pregnancy for the purpose of assessing the potential teratogenicity of these drugs. Registry data will be used to supplement animal toxicology studies and assist clinicians in weighing the potential risks and benefits of treatment for individual patients. The registry is a collaborative project of the pharmaceutical manufacturers with an advisory committee of obstetric and pediatric practitioners. The registry does not use patient names, and registry staff obtains birth outcome follow-up from the reporting physician. Referrals should be directed to Antiretroviral Pregnancy Registry, 1410 Commonwealth Drive, Wilmington, NC 28403; telephone (800)-258-4263; fax (800) 800-1052.

Update on PACTG 076 Results and Other Studies Relevant to ZDV Chemoprophylaxis of Perinatal HIV-1 Transmission

In 1996, final results were reported for all 419 infants enrolled in PACTG 076. The results concur with those initially reported in 1994; the Kaplan-Meier estimated HIV transmission rate for infants who received placebo was 22.6% compared with 7.6% for those who received ZDV-a 66% reduction in risk for transmission (47).

The mechanism by which ZDV reduced transmission in PACTG 076 has not been fully defined. The effect of ZDV on maternal HIV-1 RNA does not fully account for the observed efficacy of ZDV in reducing transmission. Preexposure prophylaxis of the fetus or infant may be a substantial component of protection. If so, transplacental passage of antiretroviral drugs would be crucial for prevention of transmission. Additionally, in placental perfusion studies, ZDV has been metabolized into the active triphosphate within the placenta (48, 49), which could provide additional protection against in utero transmission. This phenomenon may be unique to ZDV, because metabolism to the active triphosphate form within the placenta has not been observed in the other nucleoside analogues that have been evaluated (i.e., ddI and ddC) (50, 51). The presence of ZDV-resistant virus was not necessarily associated with failure to prevent transmission. In a preliminary evaluation of genotypic resistance in pregnant women in PACTG 076, ZDV-resistant virus was present at delivery in only one of seven women who had transmitted virus to their newborns, had received ZDV, and had samples that could be evaluated; this woman had ZDV-resistant virus when the study began despite having had no prior ZDV therapy (52). Additionally, the one woman in this evaluation in whom the virus developed genotypic resistance to ZDV during the study period did not transmit HIV-1 to her infant.

In PACTG 076, similar rates of congenital abnormalities occurred in infants with and without in utero ZDV exposure. Data from the Antiretroviral Pregnancy Registry also have demonstrated no increased risk for congenital abnormalities among infants born to women who receive ZDV antenatally compared with the general population (53). Data for uninfected infants from PACTG 076 followed from birth to a median age of 4.2 years (range 3.2-5.6 years) have not indicated any differences in growth, neurodevelopment, or immunologic status among infants born to mothers who received ZDV compared with those born to mothers who received placebo (54). No malignancies have been observed in short-term (i.e., up to six years of age) follow-up of more than 727 infants from PACTG 076 and from a prospective cohort study involving infants with in utero ZDV exposure (55). However, follow-up is too limited to provide a definitive assessment of carcinogenic risk with human exposure. Long-term follow-up continues to be recommended for all infants who have received in utero ZDV exposure (or in utero exposure to any of the antiretroviral drugs).

The effect of temporary administration of ZDV during pregnancy to reduce perinatal transmission on the induction of viral resistance to ZDV and long-term maternal health requires further evaluation. Data from an analysis of PACTG 288 (a study that followed women enrolled in PACTG 076 postpartum; median follow-up, 4.2 years) indicate no substantial differences in CD4+ T-cell lymphocyte count, time to progression to AIDS, or death in women who received ZDV compared with those who received placebo (56). Limited data regarding the development of genotypic ZDV-resistance mutations (i.e., codons 70 and/or 215) are available from a subset of women in PACTG 076 who received ZDV (52). Virus from one (3%) of 36 women receiving ZDV with paired isolates from the time of study enrollment and the time of delivery developed a ZDV genotypic resistance mutation. However, the population of women in PACTG 076 had low HIV-1 RNA copy numbers, and although the risk for inducing resistance with administration of ZDV chemoprophylaxis alone for several months during pregnancy was low in this substudy, it would likely be higher in a population of women with more advanced disease and higher levels of viral replication.

The efficacy of ZDV chemoprophylaxis for reducing HIV transmission among populations of infected women with characteristics unlike those of the PACTG 076 population has been evaluated in another perinatal protocol (i.e., PACTG 185) and in prospective cohort studies. PACTG 185 enrolled pregnant women with advanced HIV-1 disease and low CD4+ T-lymphocyte counts who were receiving antiretroviral therapy; 24% had received ZDV before the current pregnancy (57). All women and infants received the three-part ZDV regimen combined with either infusions of hyperimmune HIV-1 immunoglobulin (HIVIG) containing high levels of antibodies to HIV-1 or standard intravenous immunoglobulin (IVIG) without HIV-1 antibodies. Because advanced maternal HIV disease has been associated with increased risk for perinatal transmission, the transmission rate in the control group was hypothesized to be 11%-15% despite the administration of ZDV. At the first interim analysis, the combined group transmission rate was only 4.8% and did not substantially differ by whether the women received HIVIG or IVIG or by duration of ZDV use (57). The results of this trial confirm the efficacy of ZDV observed in PACTG 076 and extend this efficacy to women with advanced disease, low CD4+ count, and prior ZDV therapy. Rates of perinatal transmission have been documented to be as low as 3%-4% among women with HIV-1 infection who receive all three components of the ZDV regimen, including women with advanced HIV-1 disease (6,57).

International Antiretroviral Prophylaxis Clinical Trials
In a short-course antenatal/intrapartum ZDV perinatal transmission prophylaxis trial in non-breastfeeding women in Thailand, administration of ZDV 300 mg twice daily for 4 weeks antenatally and 300 mg every 3 hours orally during labor was shown to reduce perinatal transmission by approximately 50% compared to placebo (58). Transmission decreased from 19% in the placebo group to 9% in the ZDV group. A second, 4-arm factorial design trial in Thailand is comparing administration of ZDV antenatally starting at 28 or 36 weeks gestation, orally intrapartum, and to the neonate for three days or six weeks. At an interim analysis, the transmission rate was 10% in the arm receiving ZDV antenatally starting at 36 weeks and postnatally for 3 days to the infant, which was significantly higher than for the long-long arm (antenatal starting at 28 weeks and infant administration for six weeks (59). The transmission rate in the short-short arm of this study was similar to the 9% observed with short antenatal/intrapartum ZDV in the first Thai study. The short-short arm was terminated but the study continues to enroll into the other 3 arms (long-long, short-long and long-short).

A third trial in Africa (PETRA trial) in breastfeeding HIV-infected women has shown that a combination regimen of ZDV and 3TC administered starting at 36 weeks gestation, orally intrapartum, and for one week postpartum to the woman and infant reduced transmission by approximately 50% compared to placebo at age six weeks (60). Transmission at age six weeks was decreased from 17% in the placebo group to 9% with the 3-part ZDV/3TC regimen. This efficacy is similar to the efficacy observed in the Thailand study of antepartum/intrapartum short-course ZDV in non-breastfeeding women (58).

Studies have identified two possible intrapartum/postpartum regimens (either ZDV/3TC or nevirapine) that could provide an effective intrapartum/postpartum intervention for those women in whom the diagnosis of HIV is not made until very near to or during labor. The PETRA African ZDV/3TC trial in breastfeeding HIV-infected women also demonstrated that an intrapartum/postpartum regimen, started during labor and continued for one week postpartum in the woman and infant, reduced transmission at age six weeks from 17% in the placebo group to 11% with the 2-part ZDV/3TC regimen, a reduction of 38% (60). In this trial, oral ZDV/3TC administered solely during the intrapartum period was not effective in lowering transmission. Another study in Uganda, again in a breastfeeding population, demonstrated that a single 200 mg oral dose of nevirapine given to the mother at onset of labor combined with a single 2 mg/kg oral dose given to her infant at 48-72 hours of age reduced transmission by nearly 50% compared to a very short regimen of ZDV given orally during labor and to the infant for one week (61). Transmission at age six weeks was 12% in the nevirapine compared to 21% in the ZDV group.

No studies have evaluated the use of postpartum antiretroviral prophylaxis alone. Although some epidemiological data do not support efficacy of postnatal ZDV alone, other data indicate that there may be some efficacy if drug is started rapidly following birth (6, 62, 63). In a study from North Carolina, the rate of infection in HIV-exposed infants who received only postpartum ZDV chemoprophylaxis was similar to that observed in infants who received no ZDV chemoprophylaxis (6). However, another epidemiological study from New York State, found that administration of ZDV to the neonate for six weeks was associated with a significant reduction in transmission if the drug was initiated within 24 hours of birth (the majority of infants started within 12 hours) (49,50). Consistent with a possible preventive effect of rapid postexposure prophylaxis, a retrospective case-control study of health care workers from the United States, France, and the United Kingdom who had nosocomial exposure to HIV-1-infected blood, found that postexposure use of ZDV was associated with reduced odds of contracting HIV-1 (adjusted odds ratio 0.2; 95% confidence interval [CI]=0.1-0.6) (64).

Perinatal HIV-1 Transmission and Maternal HIV-1 RNA Copy Number
The correlation of HIV-1 RNA levels with risk for disease progression in nonpregnant infected adults suggests that HIV-1 RNA should be monitored during pregnancy at least as often as recommended for persons who are not pregnant (e.g., every 3-4 months or approximately once each trimester). Whether increased frequency of testing is needed during pregnancy is unclear and requires further study. Although no data indicate that pregnancy accelerates HIV-1 disease progression, longitudinal measurements of HIV-1 RNA levels during and after pregnancy have been evaluated in only a few prospective cohort studies. In one cohort of 198 HIV-1-infected women, plasma HIV-1 RNA levels were higher at six months postpartum than during antepartum in many women; this increase was observed in women regardless of ZDV use during and after pregnancy (65).

Initial data regarding the correlation of viral load with risk for perinatal transmission were conflicting, with some studies suggesting an absolute correlation between HIV-1 RNA copy number and risk of transmission (66). However, although higher HIV-1 RNA levels have been observed among women who transmitted HIV-1 to their infants, overlap in HIV-1 RNA copy number has been observed in women who transmitted and those who did not transmit the virus. Transmission has been observed across the entire range of HIV-1 RNA levels (including in women with HIV-1 RNA copy number below the limit of detection of the assay), and the predictive value of RNA copy number for transmission in an individual woman has been relatively poor (65, 67, 68). In PACTG 076, antenatal maternal HIV-1 RNA copy number was associated with HIV-1 transmission in women receiving placebo. In women receiving ZDV, the relationship was markedly attenuated and no longer statistically significant (47). An HIV-1 RNA threshold below which there was no risk for transmission was not identified; ZDV was effective in reducing transmission regardless of maternal HIV-1 RNA copy number (47, 69).

More recent data from larger numbers of ZDV-treated infected pregnant women indicate that HIV-1 RNA levels correlate with risk of transmission even among antiretroviral treated women (58, 70-72). Although the risk of perinatal transmission in women with HIV-1 RNA below the level of assay quantitation appears to be extremely low, transmission from mother to infant has been reported in women with all levels of maternal HIV-1 RNA. Additionally, while HIV-1 RNA may be an important risk factor for transmission, other factors also appear to play a role (72-74).

While there is a general correlation between plasma and genital tract viral load, discordance has also been reported, particularly between HIV proviral load in blood and genital secretions (75-78). If exposure to HIV in the maternal genital tract during delivery is a risk factor for perinatal transmission, then plasma HIV-1 RNA levels may not always be an accurate indicator of risk. Long-term changes in one compartment (e.g., such as may occur with antiretroviral treatment) may or may not be associated with comparable changes in other select body compartments. Further studies are needed to better define the effect of antiretroviral drugs on genital tract viral load and the association of such effects on the risk of perinatal HIV transmission. In the short-course ZDV Thailand trial, plasma and cervicovaginal HIV-1 RNA levels were reduced by ZDV treatment and each independently correlated with perinatal transmission (79). The use of the full ZDV chemoprophylaxis regimen, including intravenous ZDV during delivery and the administration of ZDV to the infant for the first six weeks of life, alone or in combination with other antiretrovirals, should be discussed with and offered to all infected pregnant women regardless of their HIV-1 RNA level.

Whether lowering maternal HIV-1 RNA copy number during pregnancy could reduce the risk for perinatal transmission has not been determined. In one study of 44 HIV-infected pregnant women, ZDV was effective in reducing transmission despite minimal effect on HIV-1 RNA levels (80). These results are similar to those observed in PACTG 076 (47). Thus, while determination of HIV-1 RNA copy number is important for decisions related to treatment, because ZDV decreases transmission regardless of maternal HIV-1 RNA level and because transmission may occur when HIV-1 RNA is not detectable, HIV-1 RNA levels should not be the determining factor when deciding whether to use ZDV for chemoprophylaxis. However, it is not known whether an antiretroviral regimen that more substantially suppresses viral replication would be associated with enhanced efficacy in reducing the risk for transmission. Recent epidemiological data suggest that women receiving highly active antiretroviral regimens that effectively reduce viral load may have very low rates of perinatal transmission (81, 82).

*FDA pregnancy categories:
A Adequate and well-controlled studies of pregnant women fail to demonstrate a risk to the fetus during the first trimester of pregnancy (and there is no evidence of risk during later trimesters);
B Animal reproduction studies fail to demonstrate a risk to the fetus and adequate and well-controlled studies of pregnant women have not been conducted;
C Safety in human pregnancy has not been determined, animal studies are either positive for fetal risk or have not been conducted, and the drug should not be used unless the potential benefit outweighs the potential risk to the fetus;
D Positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experiences, but the potential benefits from the use of the drug in pregnant women may be acceptable despite its potential risks;
X Studies in animals or reports of adverse reactions have indicated that the risk associated with the use of the drug for pregnant women clearly outweighs any possible benefit.

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