Breastfeeding with undetectable viral load: genuine uncertainty on risk should be communicated to women with HIV, say Swiss doctors

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Women with HIV on effective antiretroviral treatment in higher-income settings who have undetectable viral load should be supported to make their own decisions about breastfeeding based on a full discussion of the risks and benefits, rather than being discouraged from breastfeeding, a group of Swiss doctors has concluded after reviewing the available evidence.

Their opinion – and discussion of the evidence – is published in the open-access journal Swiss Medical Weekly.

They argue that in the absence of evidence that transmission does occur through breastfeeding when a woman has an undetectable viral load, the onus is on healthcare workers to provide unbiased information about the potential risks and benefits of breastfeeding to women living with HIV, and to support women in whatever choice they make.


virological suppression

Halting of the function or replication of a virus. In HIV, optimal viral suppression is measured as the reduction of viral load (HIV RNA) to undetectable levels and is the goal of antiretroviral therapy.

exclusive breastfeeding

Feeding an infant only breast milk, with no other liquids or solids, for the first six months of life.


A group of diseases characterized by high levels of blood sugar (glucose). Type 1 diabetes occurs when the body fails to produce insulin, which is a hormone that regulates blood sugar. Type 2 diabetes occurs when the body either does not produce enough insulin or does not use insulin normally (insulin resistance). Common symptoms of diabetes include frequent urination, unusual thirst and extreme hunger. Some antiretroviral drugs may increase the risk of type 2 diabetes.

equivalence trial

A clinical trial which aims to demonstrate that a new treatment is no better or worse than an existing treatment. While the two drugs may have similar results in terms of virological response, the new drug may have fewer side-effects, be cheaper or have other advantages. 


A mental health problem causing long-lasting low mood that interferes with everyday life.

In resource-limited settings the World Health Organization recommends that women living with HIV should take antiretroviral therapy and breastfeed for 12-24 months. This guidance reflects the protective effect of breastfeeding against infant mortality in resource-limited settings.

In higher-income settings national guidelines continue to discourage breastfeeding by mothers with HIV who are taking antiretroviral therapy, with few exceptions. A recent review of the scientific literature highlighted unanswered scientific questions.

But a group of Swiss doctors has now joined their British counterparts in questioning whether breastfeeding should be discouraged entirely.

The group, which includes paediatricians and specialists in obstetrics and gynaecology from some of the main hospitals providing care to people living with HIV in Switzerland, carried out a review of the scientific literature published since 2009 to identify any reported cases of HIV transmission through breastfeeding when the mother had a viral load below 50 copies/ml, was in continuous care and was fully adherent to antiretroviral treatment. They describe this as the 'optimal scenario', and point out that in an analysis of pregnant women who gave birth between 2012 and 2016 in the Swiss HIV Cohort, 95.9% of mothers already had a fully suppressed viral load at the time of delivery, indicating that this scenario is likely to be widely applicable.

Previous reviews of the scientific literature have been less strict regarding evidence of full viral suppression and have drawn attention to cases of transmission where it is difficult to be certain if the mother had a fully suppressed viral load. A randomised study of antiretroviral therapy or infant prophylaxis during breastfeeding (the PROMISE study) found that the risk of transmission was approximately 0.3% six months after delivery and 0.7% 12 months after delivery.

But the authors of the Swiss review point out that there is no evidence available on viral load suppression throughout the follow-up period in the PROMISE study, meaning that it is not possible to determine whether any transmission that took place during this study occurred in the conditions of the 'optimal scenario'. They did not identify any other documented cases of HIV transmission through breastfeeding in this scenario.

The review authors say that this leaves a situation of clinical equipoise – genuine scientific uncertainty – and that doctors should engage in shared decision-making with women living with HIV about infant feeding decisions.

The review authors suggest that the following points should be communicated to women when infant feeding is discussed, after discussing the woman’s preferences regarding feeding. Women should be informed that whatever decision they make, they will be supported by their healthcare team.

Breastfeeding – potential risks

  • There is no formal study, equivalent to the PARTNER study of sexual transmission, which has evaluated the risk of transmission through breastfeeding when viral load is fully suppressed.
  • The lack of evidence of transmission to date does not allow us to rule out the possibility of transmission.
  • The possibility of transmission through cell-associated virus cannot be ruled out; not enough is known about this possibility.
  • There is a lack of information about potential toxicities of antiretroviral drugs taken in by the infant in breast milk.
  • Adherence support is especially important in the postpartum period owing to the sleep disruption and mood disorders that may affect adherence during this period.
  • Mastitis might increase the risk of transmission.
  • Mixed feeding (breast milk plus any other liquids, such as formula, or solids) may increase the risk of transmission so exclusive breastfeeding for the first four months is recommended in Switzerland.

Breastfeeding – potential benefits

  • Breastfeeding has numerous benefits to the infant and is recommended in most European countries for HIV-negative mothers.
  • Breastfeeding is a simple, easy and free way of providing nutrition to the infant.
  • Breastfeeding benefits the mother by reducing the risk of postpartum depression.
  • Breastfeeding may reduce the future risk of breast cancer, especially for younger women.
  • Breastfeeding reduces the risk of type 2 diabetes for mothers and helps control blood sugar.

BHIVA guidelines

Recent guidance from the British HIV Association (BHIVA) advises that, in the UK and similar settings, the safest way to feed infants born to mothers with HIV is with formula milk. Nonetheless, women with an undetectable viral load who choose to breastfeed should be supported to do so. The guidance emphasises the importance of breastfeeding mothers remaining in close contact with their medical teams. Both mother and baby should come in for monthly testing. Mothers should breastfeed for as short a time as possible, ideally no more than six months.



BHIVA's recommendations say: “In the UK and other resource rich settings the safest way to feed infants born to mothers with HIV is with formula milk, as this eliminates on-going risk of HIV exposure after birth.” (9.4.1) “Women who are virologically suppressed on cART with good adherence and who choose to breastfeed may be supported to do so, but should be informed about the low risk of transmission of HIV through breastfeeding in this situation.” (9.4.3)




Kahlert C et al. Is breastfeeding an equipoise option in effectively treated HIV-infected mothers in a high-income setting? Swiss Medical Weekly, 148:w14648, 2018. (Article full text.)