Maternal HIV Testing and Identification of Perinatal HIV Exposure
|Rating of Recommendations: A = Strong; B = Moderate; C = Optional
Rating of Evidence: I = One or more randomized trials in children† with clinical outcomes and/or validated endpoints; I* = One or more randomized trials in adults with clinical outcomes and/or validated laboratory endpoints with accompanying data in children† from one or more well-designed, nonrandomized trials or observational cohort studies with long-term clinical outcomes; II = One or more well-designed, nonrandomized trials or observational cohort studies in children† with long-term outcomes; II* = One or more well-designed, nonrandomized trials or observational studies in adults with long-term clinical outcomes with accompanying data in children† from one or more similar nonrandomized trials or cohort studies with clinical outcome data; III = Expert opinion
†Studies that include children or children and adolescents, but not studies limited to post-pubertal adolescents
HIV Testing in Pregnancy
HIV infection should be identified prior to pregnancy (see Preconception Counseling and Care for Women of Childbearing Age Living with HIV) or as early in pregnancy as possible. This provides the best opportunity to improve maternal health and pregnancy outcomes, to prevent infant acquisition of HIV, and to identify HIV infection and start therapy as soon as possible in infants who acquire HIV. Universal voluntary HIV testing is recommended as the standard of care for all pregnant women in the United States by the Panel on Antiretroviral Therapy and Medical Management of Children Living with HIV and the Panel on Treatment of Pregnant Women with HIV Infection and Prevention of Perinatal Transmission (the Panels), the Centers for Disease Control and Prevention (CDC), the American Academy of Pediatrics, the American College of Obstetricians and Gynecologists, and the U.S. Preventive Services Task Force.1-5 All HIV testing should be performed in a manner that is consistent with state and local laws. CDC recommends the “opt-out” approach, which involves notifying pregnant women that HIV testing will be performed as part of routine care unless they choose not to be tested for HIV.2 The “opt-out” approach during pregnancy is allowed in some jurisdictions.6 The "opt-in" approach involves obtaining specific consent before testing, and this approach has been associated with lower testing rates.7,8 The mandatory newborn HIV testing approach, which has been adopted by several states, involves testing newborns with or without maternal consent. In some areas, this applies to all newborns; in others, it applies only to the infants of mothers who have declined prenatal or intrapartum testing.
Partners of pregnant women should also be encouraged to undergo HIV testing when their status is unknown, consistent with the 2006 CDC recommendations for HIV testing of all individuals in the United States. Testing will facilitate linkage to care if a partner is found to have HIV infection. Because women are more susceptible to HIV acquisition during pregnancy and the postpartum period,9 clinicians can also initiate a discussion about preventative interventions, including pre-exposure prophylaxis, if the pregnant woman does not have HIV but is at high risk for HIV acquisition.
Clinicians should assess a woman’s risk of acute HIV infection, particularly late in pregnancy, because a pregnant woman may receive a negative result for expedited or rapid HIV testing when she is in the window period (the window period lasts up to 15 days post-infection when using the combined antigen/antibody immunoassay, and up to 28 days when using other assays). However, during this period she will be viremic,10 with a high risk of perinatal transmission to her newborn. The HIV RNA assay can detect the presence of HIV as early as 10 days post-infection, so this test should be used when acute HIV infection is suspected. See Acute HIV Infection for more information.
Providers should be aware that gaps in maternal HIV testing do occur and can contribute to missed opportunities for preventing perinatal HIV transmission.11-14 Maternal HIV testing should be performed as early as possible during pregnancy, wherever a woman seeks care (including emergency departments and prenatal clinics), to avoid missed opportunities to identify pregnant women with HIV. Repeat HIV testing should be performed in the third trimester for women who are at increased risk of acquiring HIV or who are living in areas of high HIV incidence. Women with unknown or undocumented HIV status who present to care in labor should be tested during delivery or as soon as possible after delivery.11-14
Determining antenatal maternal HIV status enables:
- Women with HIV to receive appropriate antiretroviral therapy (ART) and prophylaxis against opportunistic infections;
- Initiation of treatment in the identified women, which may also decrease the risk of transmission to their partners;2,15,16
- Referral of partners for testing, which allows them to initiate treatment if the results are positive or preventive interventions if the results are negative;
- Provision of ART to the mother during pregnancy and labor, and provision of an appropriate antiretroviral (ARV) drug regimen to the newborn to reduce the risk of perinatal transmission;
- Counseling of women with HIV about the indications for (and potential benefits of) scheduled elective cesarean delivery to reduce the risk of perinatal transmission of HIV;17-19
- Counseling of women with HIV about the risks of HIV transmission through breast milk (breastfeeding is not recommended for women with HIV living in the United States);20 and
- Early diagnostic evaluation of infants exposed to HIV (see Diagnosis of HIV Infection in Infants and Children), as well as testing of other children, to permit prompt initiation of ART and any indicated prophylaxis measures.1,21-23
New technology has made it possible to detect HIV earlier and has reduced the performance time for laboratory-based assays, which can now be completed in <1 hour. Accordingly, the Panels now base their recommendations for HIV testing on CDC’s 2014 Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations.24 The guidelines recommend that clinicians initiate HIV testing with an immunoassay that is capable of detecting HIV-1 antibodies, HIV-2 antibodies, and HIV-1 p24 antigen (referred to as an antigen/antibody combination immunoassay). Individuals with a reactive antigen/antibody combination immunoassay should be tested further with an HIV-1/HIV-2 antibody differentiation assay (referred to as supplemental testing). Individuals with a reactive antigen/antibody combination immunoassay and a nonreactive differentiation test should be tested with a Food and Drug Administration-approved plasma HIV RNA assay to establish a diagnosis of acute HIV infection (see CDC’s Recommended Laboratory HIV Testing Algorithm for Serum or Plasma Specimens).
Discordant HIV testing results can be seen, requiring careful evaluation and often repeat tests. Early in HIV infection, prior to HIV seroconversion, the antigen-antibody screen will be negative and the HIV RNA assay will be positive. This is seen in true infection, since the HIV RNA assay is positive before the antigen/antibody screen. The test combination of a positive antigen-antibody screen, negative antibody differentiation assay, and positive HIV RNA assay also can be seen early in HIV infection, since the IgG-based antibody differentiation assay is positive later in infection than the antigen capture or the IgM result in the antigen-antibody screen.
Clinicians should be aware that as more individuals undergo repeat HIV testing, the number of false-positive screens will increase. The combination of a positive antigen-antibody screen with a negative antibody differentiation assay and a negative HIV RNA assay is seen in persons without HIV infection who have a false-positive antigen-antibody screen.
These examples should make it clear that for any positive HIV 1/2 antigen-antibody screen, an HIV RNA assay should be done, since it is the HIV RNA assay that is needed to resolve questions raised by discordant results on the antigen-antibody screen and the antibody differentiation assay.
The antigen/antibody combination immunoassay is the test of choice and can be done quickly (referred to as an expedited test), but it requires trained laboratory staff and therefore may not be available in some hospitals 24 hours a day. When this test is unavailable, initial testing should be performed by the most sensitive expedited or rapid test available. Every delivery unit needs to have access to an HIV test that can be done rapidly (i.e., in <1 hour) 24 hours a day. If the test result is positive, the test to confirm HIV infection should be performed as soon as possible (as with all initial assays with positive results). Older antibody tests have lower sensitivity in the context of recent acquisition of HIV than antigen/antibody combination immunoassays. Therefore, testing that follows the 2014 CDC algorithm should be considered if HIV risk cannot be ruled out. Results of maternal HIV testing should be documented in the newborn’s medical record and communicated to the newborn’s primary care provider.
Repeat HIV Testing in the Third Trimester
Repeat HIV testing during the third trimester, before 36 weeks gestation, is recommended (see Acute HIV Infection)25 for pregnant women with negative results on their initial HIV antibody tests who:5
- Are at high risk of acquiring HIV (e.g., those who are injection drug users or partners of injection drug users, those who exchange sex for money or drugs, those who are sex partners of individuals with HIV, those who have had a new sex partner or more than one sex partner during the current pregnancy, or those who have a suspected or diagnosed sexually transmitted infection during pregnancy); or
- Are receiving health care in facilities in which prenatal screening identifies one or more pregnant woman with HIV per 1,000 women screened, or who reside in a jurisdiction that has a high incidence of HIV or AIDS in women between the ages of 15 and 45 years (a list of jurisdictions where such screening is recommended is found in the 2006 CDC recommendations; a more up-to-date list is forthcoming), or who reside in states that require third-trimester testing; or
- Have signs or symptoms of acute HIV (e.g., fever, lymphadenopathy, skin rash, myalgia, headaches, oral ulcers, leukopenia, thrombocytopenia, elevated transaminase levels).2,26-28
Women who decline testing earlier in pregnancy should be offered testing again during the third trimester. An antigen/antibody combination immunoassay should be used, as these tests have a higher sensitivity in the setting of acute HIV infection than older antibody tests.24,29 When acute HIV infection is suspected during pregnancy, during the intrapartum period, or while breastfeeding, a plasma HIV RNA test result should be performed in conjunction with an antigen/antibody combination immunoassay (see Acute and Recent [Early] HIV Infection in the Adult and Adolescent Antiretroviral Guidelines).
Providers should be proactive in assessing a woman’s HIV acquisition risk and implementing third-trimester HIV retesting when indicated in areas where it is not routine. A recent study in Baltimore found that only 28% of women were retested for HIV despite the high incidence of HIV in Maryland and a high frequency of clinical risk factors.14,30 A study of data from 2007 to 2014 on Florida children with perinatal HIV exposure found that perinatal HIV transmission was associated with poor or late prenatal care, diagnosis of maternal HIV during labor and delivery or after birth, and, in some cases, acute maternal infection (as indicated by negative results for initial tests). In addition, the study noted that third-trimester HIV tests were not performed in a portion of the patients.30 Repeat HIV testing at other times during pregnancy should also be considered when clinically indicated. For example, repeat testing should be performed when a woman presents with symptoms that are suggestive of a sexually transmitted infection (STI), when a woman presents with a confirmed STI diagnosis, or when a woman presents with symptoms that are consistent with acute HIV infection.
HIV Testing During Labor in Women with Unknown HIV Status
Women in labor whose HIV status is undocumented should undergo HIV testing in order to identify HIV infection in the mothers and HIV exposure in their infants. HIV testing during labor has been found to be feasible, accurate, timely, and useful both in ensuring prompt initiation of intrapartum maternal ARV for fetal/infant prophylaxis (see Intrapartum Antiretroviral Therapy/Prophylaxis) and in developing an appropriate ARV regimen for infants who are at high risk of perinatal HIV transmission (see Table 11).1-3,21,27,31,32
Policies and procedures must be in place to ensure that staff are prepared to provide patient education and expedited HIV testing, that appropriate ARV drugs are available whenever needed, and that follow-up procedures are in place for women who receive an HIV diagnosis and for their infants.
If the antigen/antibody combination immunoassay is not available, initial testing should be performed by the most sensitive expedited test available.
A positive expedited HIV test result must be followed by a supplemental test.24 Immediate initiation of maternal intravenous intrapartum zidovudine is recommended to prevent perinatal transmission of HIV pending the supplemental result (see Intrapartum Antiretroviral Therapy/Prophylaxis).1-4,21,27 Pending results of supplemental maternal testing, infants should receive an ARV regimen that is appropriate for infants who are at higher risk of perinatal HIV transmission as soon as possible (see Antiretroviral Management of Newborns with Perinatal HIV Exposure or Perinatal HIV or contact the National Perinatal HIV Hotline). No further testing is required for specimens that are nonreactive (negative) on the initial immunoassay, unless acute HIV infection is suspected (see Acute HIV Infection).24
HIV Testing During the Postpartum Period
Women who have not been tested for HIV before or during labor should be offered expedited testing during the immediate postpartum period. Maternal testing should be done using the antigen/antibody combination immunoassay to screen for established and acute HIV; results should be obtained in <1 hour. If acute HIV infection is a possibility, then a plasma HIV RNA test should be sent as well. When mothers are unavailable for testing, their newborns should undergo expedited HIV testing using the antigen/antibody combination immunoassay.1,21,27 Postnatal ARV drugs need to be initiated as soon as possible—ideally ≤6 hours after birth—to be effective in preventing perinatal transmission. When an initial HIV test is positive in mother or infant, it is strongly recommended that clinicians initiate an ARV regimen that is appropriate for infants who are at higher risk of perinatal HIV transmission and counsel the mother against breastfeeding. Both actions can be taken before the results of supplemental maternal HIV tests have confirmed the presence of HIV (see Antiretroviral Management of Newborns with Perinatal HIV Exposure or Perinatal HIV). Breast milk can be expressed while supplemental HIV diagnostic testing is being completed, but it should not be given to the infant until testing confirms that the mother is HIV negative. If supplemental test results are negative and acute HIV is excluded, infant ARV drugs can be discontinued. In the absence of ongoing maternal HIV exposure, breastfeeding can be initiated.
Infant HIV Testing when Maternal HIV Test Results are Unavailable
When maternal HIV test results are unavailable (e.g., for infants and children who are in foster care) or their accuracy cannot be evaluated (e.g., for infants and children who were adopted from countries where results are not reported in English), HIV testing using the antigen/antibody combination immunoassay is indicated to identify HIV exposure and possible infection in these infants or children.1 Mechanisms should be developed to facilitate prompt HIV screening for infants who have been abandoned and who are in the custody of the state. The choice of test will vary based on the age of the child (see Diagnosis of HIV Infection in Infants and Children).
Acute Maternal HIV Infection During Pregnancy or Breastfeeding
Women are more susceptible to HIV infection during pregnancy and the early postpartum period.9 Risk of HIV exposure should be assessed in all women who are considering becoming pregnant, as well as in all pregnant women who previously tested HIV negative. Women with risk factors for HIV acquisition should receive prevention counseling and appropriate interventions, including pre-exposure prophylaxis if indicated (see Preconception Counseling and Care for Women of Childbearing Age Living with HIV). Women who have acute HIV during pregnancy or lactation have an increased risk of perinatal transmission and secondary sexual transmission of HIV (see Acute HIV Infection).25,33-36 The antigen/antibody combination immunoassay will detect acute HIV infection earlier than other immunoassays, within approximately 15 days of acquisition. When acute HIV infection is suspected, a plasma HIV RNA test should be sent as well, because virologic tests can detect the presence of HIV approximately 5 days earlier than the antigen/antibody combination immunoassay. Women with possible acute HIV infection who are breastfeeding should cease breastfeeding immediately until HIV infection is confirmed or excluded.20 Breast milk can be expressed while HIV diagnostic testing is completed. Breastfeeding can resume if HIV infection is excluded and there is no ongoing maternal exposure to HIV. Care of pregnant or breastfeeding women with acute or early HIV and their infants should follow the recommendations in the Perinatal Guidelines (see Acute HIV Infection and Counseling and Managing Women Living with HIV in the United States Who Desire to Breastfeed).
Clinicians should be aware of public health surveillance systems and regulations that may exist in their jurisdictions for reporting infants who have been exposed to HIV; this is in addition to mandatory reporting of persons with HIV, including infants. Reporting infants who have been exposed to HIV allows the appropriate public health functions to be accomplished.
- American Academy of Pediatrics Committee on Pediatric AIDS. HIV testing and prophylaxis to prevent mother-to-child transmission in the United States. Pediatrics. 2008;122(5):1127-1134. Available at: http://www.ncbi.nlm.nih.gov/pubmed/18977995.
- Branson BM, Handsfield HH, Lampe MA, et al. Revised recommendations for HIV testing of adults, adolescents, and pregnant women in health-care settings. MMWR Recomm Rep. 2006;55(RR-14):1-17; quiz CE11-14. Available at: http://www.ncbi.nlm.nih.gov/pubmed/16988643.
- Chou R, Cantor AG, Zakher B, Bougatsos C. Screening for HIV in pregnant women: systematic review to update the 2005 U.S. Preventive services task force recommendation. Ann Intern Med. 2012;157(10):719-728. Available at: http://www.ncbi.nlm.nih.gov/pubmed/23165663.
- U.S. Preventive Services Task Force. Screening for HIV: recommendation statement. 2013.
- American College of Obstetrics and Gynecology: Committee on Obstetric Practice, HIV Expert Work Group. ACOG committee opinion No. 752: prenatal and perinatal human immunodeficiency virus testing. Obstet Gynecol. 2018;132(3):e138-e142. Available at: https://www.ncbi.nlm.nih.gov/pubmed/30134428.
- Clinical Consultation Center. Compendium of state HIV testing laws. Perinatal quick reference guide: a guide to states' perinatal HIV testing laws for clinicians. 2011. Available at: http://nccc.ucsf.edu/wp-content/uploads/2014/03/State_HIV_Testing_Laws_Perinatal_Quick_Reference.pdf.
- Boer K, Smit C, van der Flier M, de Wolf F, Athena cohort study group. The comparison of the performance of two screening strategies identifying newly-diagnosed HIV during pregnancy. Eur J Public Health. 2011;21(5):632-637. Available at: http://www.ncbi.nlm.nih.gov/pubmed/21051473.
- Yudin MH, Moravac C, Shah RR. Influence of an "opt-out" test strategy and patient factors on human immunodeficiency virus screening in pregnancy. Obstet Gynecol. 2007;110(1):81-86. Available at: http://www.ncbi.nlm.nih.gov/pubmed/17601900.
- Thomson KA, Hughes J, Baeten JM, et al. Increased risk of HIV acquisition among women throughout pregnancy and during the postpartum period: a prospective per-coital-act analysis among women with HIV-infected partners. J Infect Dis. 2018;218(1):16-25. Available at: https://www.ncbi.nlm.nih.gov/pubmed/29514254.
- Centers for Disease Control and Prevention and Association of Public Health Laboratories. Laboratory testing for the diagnosis of HIV infection: updated recommendations. 2014. Available at: https://stacks.cdc.gov/view/cdc/23447.
- Whitmore SK, Taylor AW, Espinoza L, Shouse RL, Lampe MA, Nesheim S. Correlates of mother-to-child transmission of HIV in the United States and Puerto Rico. Pediatrics. 2012;129(1):e74-81. Available at: https://www.ncbi.nlm.nih.gov/pubmed/22144694.
- Ezeanolue EE, Pharr JR, Hunt A, Patel D, Jackson D. Why are children still being infected with HIV? Impact of an integrated public health and clinical practice intervention on mother-to-child HIV transmission in Las Vegas, Nevada, 2007-2012. Ann Med Health Sci Res. 2015;5(4):253-259. Available at: https://www.ncbi.nlm.nih.gov/pubmed/26229713.
- Taylor AW, Nesheim SR, Zhang X, et al. Estimated perinatal HIV infection among infants born in the United States, 2002-2013. JAMA Pediatr. 2017;171(5):435-442. Available at: https://www.ncbi.nlm.nih.gov/pubmed/28319246.
- Liao C, Golden WC, Anderson JR, Coleman JS. Missed opportunities for repeat HIV testing in pregnancy: implications for elimination of mother-to-child transmission in the United States. AIDS Patient Care STDS. 2017;31(1):20-26. Available at: https://www.ncbi.nlm.nih.gov/pubmed/27936863.
- Cohen MS, Chen YQ, McCauley M, et al. Prevention of HIV-1 infection with early antiretroviral therapy. N Engl J Med. 2011;365(6):493-505. Available at: http://www.ncbi.nlm.nih.gov/pubmed/21767103.
- Baggaley RF, White RG, Hollingsworth TD, Boily MC. Heterosexual HIV-1 infectiousness and antiretroviral use: systematic review of prospective studies of discordant couples. Epidemiology. 2013;24(1):110-121. Available at: http://www.ncbi.nlm.nih.gov/pubmed/23222513.
- Jamieson DJ, Read JS, Kourtis AP, Durant TM, Lampe MA, Dominguez KL. Cesarean delivery for HIV-infected women: recommendations and controversies. Am J Obstet Gynecol. 2007;197(3 Suppl):S96-100. Available at: http://www.ncbi.nlm.nih.gov/pubmed/17825656.
- Tubiana R, Le Chenadec J, Rouzioux C, et al. Factors associated with mother-to-child transmission of HIV-1 despite a maternal viral load <500 copies/mL at delivery: a case-control study nested in the French perinatal cohort (EPF-ANRS CO1). Clin Infect Dis. 2010;50(4):585-596. Available at: http://www.ncbi.nlm.nih.gov/pubmed/20070234.
- Townsend CL, Cortina-Borja M, Peckham CS, de Ruiter A, Lyall H, Tookey PA. Low rates of mother-to-child transmission of HIV following effective pregnancy interventions in the United Kingdom and Ireland, 2000-2006. AIDS. 2008;22(8):973-981. Available at: http://www.ncbi.nlm.nih.gov/pubmed/18453857.
- Committee On Pediatric AIDS. Infant feeding and transmission of human immunodeficiency virus in the United States. Pediatrics. 2013;131(2):391-396. Available at: http://www.ncbi.nlm.nih.gov/pubmed/23359577.
- Havens PL, Mofenson LM, American Academy of Pediatrics Committee on Pediatric AIDS. Evaluation and management of the infant exposed to HIV-1 in the United States. Pediatrics. 2009;123(1):175-187. Available at: http://www.ncbi.nlm.nih.gov/pubmed/19117880.
- Hegazi A, Forsyth S, Prime K, Bashh Adolescent Special Interest Group. Testing the children of HIV-infected parents: 6 years on from 'don't forget the children'. Sex Transm Infect. 2015;91(2):76-77. Available at: http://www.ncbi.nlm.nih.gov/pubmed/25316913.
- Panel on Opportunistic Infections in Adults and Adolescents with HIV. Guidelines for the prevention and treatment of opportunistic infections in adults and adolescents with HIV: recommendations from the Centers for Disease Control and Prevention, the National Institutes of Health, and the HIV Medicine Association of the Infectious Diseases Society of America. 2018. Available at: adult_oi.pdf.
- Branson BM, Owen SM, Wesolowski LG, et al. Laboratory testing for the diagnosis of HIV infection: updated recommendations. Centers for Disease Control and Prevention. 2014.
- Birkhead GS, Pulver WP, Warren BL, Hackel S, Rodriguez D, Smith L. Acquiring human immunodeficiency virus during pregnancy and mother-to-child transmission in New York: 2002–2006. Obstet Gynecol. 2010;115(6):1247-1255. Available at: http://www.ncbi.nlm.nih.gov/pubmed/20502297.
- Sansom SL, Jamieson DJ, Farnham PG, Bulterys M, Fowler MG. Human immunodeficiency virus retesting during pregnancy: costs and effectiveness in preventing perinatal transmission. Obstet Gynecol. 2003;102(4):782-790. Available at: http://www.ncbi.nlm.nih.gov/pubmed/14551009.
- American College of Obstetrics: Gynecology Committee on Obstetric Practice. ACOG committee opinion no. 418: prenatal and perinatal human immunodeficiency virus testing: expanded recommendations. Obstet Gynecol. 2008;112(3):739-742. Available at: http://www.ncbi.nlm.nih.gov/pubmed/18757690.
- Richey LE, Halperin J. Acute human immunodeficiency virus infection. Am J Medical Sci. 2013;345(2):136-142. Available at: http://www.ncbi.nlm.nih.gov/pubmed/23095473.
- Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the use of antiretroviral agents in adults and adolescents living with HIV. 2018. Available at: AdultandAdolescentGL.pdf.
- Trepka MJ, Mukherjee S, Beck-Sague C, et al. Missed opportunities for preventing perinatal transmission of human immunodeficiency virus, Florida, 2007-2014. South Med J. 2017;110(2):116-128. Available at: https://www.ncbi.nlm.nih.gov/pubmed/28158882.
- Yee LM, Miller ES, Statton A, et al. Sustainability of statewide rapid HIV testing in labor and delivery. AIDS Behav. 2018;22(2):538-544. Available at: https://www.ncbi.nlm.nih.gov/pubmed/28986656.
- Scott RK, Crochet S, Huang CC. Universal rapid human immunodeficiency virus screening at delivery: a cost-effectiveness analysis. Infect Dis Obstet Gynecol. 2018;2018:6024698. Available at: https://www.ncbi.nlm.nih.gov/pubmed/29731602.
- Lockman S, Creek T. Acute maternal HIV infection during pregnancy and breast-feeding: substantial risk to infants. J Infect Dis. 2009;200(5):667-669. Available at: http://www.ncbi.nlm.nih.gov/pubmed/19627246.
- Taha TE, James MM, Hoover DR, et al. Association of recent HIV infection and in-utero HIV-1 transmission. AIDS. 2011;25(11):1357-1364. Available at: http://www.ncbi.nlm.nih.gov/pubmed/21572305.
- Humphrey JH, Marinda E, Mutasa K, et al. Mother to child transmission of HIV among Zimbabwean women who seroconverted postnatally: prospective cohort study. BMJ. 2010;341:c6580. Available at: http://www.ncbi.nlm.nih.gov/pubmed/21177735.
- Drake AL, Wagner A, Richardson B, John-Stewart G. Incident HIV during pregnancy and postpartum and risk of mother-to-child HIV transmission: a systematic review and meta-analysis. PLoS Med. 2014;11(2):e1001608. Available at: http://www.ncbi.nlm.nih.gov/pubmed/24586123.