**2. Developing the guide**

The attempt at improving epidemiological rates of HIV/AIDS through the prevention and treatment of the disease is one of the eight Millennium Development Goals proposed by the World Health Organization. Worldwide, the virtual eradication of mother-to-child transmis‐ sion is one of the goals to be accomplished [1, 2].

The present guide will be developed based on the method proposed by Harbour et al., which in turn is based on the formulation of various questions that will be answered according to levels of evidence, grading of recommendation, and experts' opinions [3].

Vertical transmission (VT) of HIV is defined as that occurring from mother to child during gestation, delivery, or breastfeeding. The VT rates range between 13% and 48%. [4-7]. Preven‐ tive strategies have been set out to lower VT rates to less than 2%. Pregnancy, delivery, and breastfeeding are the most susceptible periods for VT of HIV [8, 9]. Maternal viral load (VL) is the main independent risk factor for transmission. Certain sexually transmitted diseases (STD) also increase the risk of VT. Likewise, low maternal CD4 cell counts also constitute a risk factor for VT, which is independent from VL [10].

The prevalence of vertical transmission (VT) in the various regions of the world varies according to geographic site and specifically according to the contribution of economic resources invested by different countries worldwide in the various strategies for healthcare policies, aiming at the prevention and treatment of infected mothers [2].

In countries with low infection prevalence rates such as Chile, efforts have been targeted to the decrease of vertical transmission (VT), which is responsible for 99% of HIV infections among children younger than 13 years old [5, 11].

Mother-to-child transmission as route of exposure has decreased, from rates of approximately 30% in 1996, prior to the first VT prevention protocol (ACTG 076), to 0.7% for HIV and 0.6% for AIDS, during the 2006-2010 period [4, 12-14].

To optimize prevention of VT, the clinical approach to a seropositive pregnant woman must be based on a thorough assessment of her initial health status, with a full physical examination, focusing particularly on those signs that point toward an opportunistic infectious condition and evaluating her current immune status.

The strategy for prevention of VT has been based on the continuous review of the pooled evidence and has followed the impact factor of such evidence to suggest valid recommen‐ dations from expert opinions. It is of key importance to further evaluate new behaviors tending to identify, among other aspects: the eventual induction of resistance and toxicity of antivirals both in the pregnant mother as well as in the newborn, and their potential effect on subsequent quality of life, the use of micronutrients and the identification of their impact on VT decrease, and the evaluation of vaginal delivery as an option in pregnant women with a low viral load [2, 14-20].

Once the effectiveness of biomedical patient benefits in VT prevention has been demonstrated, it is important to ensure the collection of epidemiological history in order to generate an adequate means of notification, which constitutes data required for reassessing the design and the effectiveness of preventive programs. To attain such goals, it is key to maintain and improve diagnosis and primary prevention of infection in women in childbearing age. Furthermore, it is important to avoid the high rate of unwanted pregnancies and abortions, which represent indirect indicators of risk behaviors in such population. Likewise, one should aim at reaching 100% of screening during the first trimester, at the possibility of repeating such screening during the third trimester and at training maternity staff in rapid testing for the detection of carrier status during labor for pregnant women not having previously undergone such screening [2].
