HIV can be transmitted to an infant during childbirth, especially if waters break more than four hours before delivery and if labour is difficult or prolonged.

HIV transmission is most likely to happen when mothers are not on antiretroviral treatment and have higher viral loads. However, it can occur when the child is delivered vaginally even when viral load is undetectable, possibly because of HIV localised in the genital tract.

In the developed world, women who have elective or scheduled Caesarean sections before going into labour are much less likely to transmit HIV to their infants than women who deliver vaginally.

Studies have now shown that even when viral load is undetectable in women on antiretroviral therapy, a planned Caesarean section can lower the risk of HIV transmission to her infant.

However, given the relatively low risk of HIV transmission when the mothers viral load is undetectable on stable antiretroviral therapy, most guidelines advise that vaginal delivery should still be considered as an option for women with undetectable viral loads, and that they should be informed of the risks as well as the benefits associated with Caesarean sections.

In poor and middle-income countries, however, it is unclear what is the safest option for a mother and her child as invasive medical procedures present a risk of infection and other complications.

Mode of delivery in European and North American women

Studies performed before viral load testing and combination antiretroviral therapy became a routine part of clinical practice have shown that planned Caesarean delivery, performed before the onset of labour and rupture of membranes, is consistently associated with a significant decrease in HIV transmission compared with other types of delivery. Reductions ranged from 55 to 80% (International Perinatal Group 1999; Leyes 2002; Mandelbrot 1998; Parrazini 1999).

Widespread access to antiretroviral therapy has lowered the rate of mother-to-child transmission to such an extent that there has been some debate whether elective Caesarean delivery offers any further benefit, if the mother has an undetectable viral load.

However, recent data from the European Collaborative Study of over 1570 women now show that elective Caesarean delivery reduces the risk of mother-to-baby transmission of HIV by 40% when a woman has an undetectable viral load compared to vaginal delivery. In this study, the use of antiretroviral medication was significantly associated with a twelvefold reduced risk of mother-to-baby transmission, particularly amongst those who started therapy before pregnancy (European Collaborative Study 2005).

Data from a similarly large study of over 1390 women in the United States, the Women and Infant Transmission Study, have shown similar rates of transmission, although elective Caesarean section was a much less common procedure in this study (Magder 2005).

Elective Caesarean sections for all?

Despite the strength of evidence, there has been some disagreement over whether the use of elective Caesarean delivery for all pregnancies in HIV-positive women should be recommended. This is primarily due the success of potent antiretroviral therapy, which has reduced HIV transmissions to zero in some studies, leading doctors to deem Caesarian secrions unnecessary in women with a good virological response to HIV treatment (Mofenson 1999; Morris 2000; Stek 1999).

Recent evidence from London's Chelsea and Westminster Hospital has in fact shown that no single infant born to a mother with an undetectable viral load at the time of delivery was infected with HIV. Since 25% of the deliveries were pre-term, the investigators emphasise that it is necessary to start antiretroviral therapy no later than week 24 of pregnancy to allow time for adequate viral suppression and the option of a vaginal delivery. The investigators believe that women with a viral load below 50 copies/ml and no indications for an elective Caesarean section should be offered a vaginal delivery if that is their preference (Browne 2005).

However, complications during vaginal deliveries can cause rare cases of HIV transmission despite undetectable viral loads, possibly as a result of detectable viral loads in the birth canal (Chuachoowong 2000).

Does mode of delivery affect the mother's health?

At the conclusion of their recent study, the authors of the European Collaborative Study report wrote that the decision regarding mode of delivery rests with the woman and her doctor, and that the doctor should inform the woman of the potential risks and benefits of the options available. However, it is important to realise that there has been less analysis of the risks associated with planned Caesarean sections among HIV-positive than -negative women.

In an earlier report from the European Study Collaborative, complications following delivery were uncommon, and there were no serious adverse events in either HIV-positive or -negative women. Although there was a higher rate of fever following delivery amongst women who had a caesarean section, there were no differences in complications between treated and untreated women. (Parrazini 2000). Similarly, a London clinic reported that Caesarean section under spinal anaesthetic was not associated with increased risk of complications in HIV-infected women (Avidan 2002).

A large review of HIV-positive women from the United States also reported that Caesarean section was associated with increased risk of negative effects after birth, particularly of fever without infection (Read 2001). Similarly, in an analysis of 497 women from ACTG 185, morbidity rates due to infection were greater with Caesarian than with vaginal deliveries (Watts 2000).

A retrospective German study found that HIV-positive women were more likely to experience complications after a caesarean section than HIV-negative women (Grubert 2002), while the European HIV in Obstetrics Group reported a doubled rate of complications in HIV-positive women over HIV-negative controls. This increased to a fivefold increase in women undergoing Caesarian section. These complications included anaemia, which was linked to excessive blood loss during surgery, use of antiretroviral therapy, and immunosuppression. In women giving birth vaginally, there were no major complications in either HIV-positive or -negative women, although the HIV-positive women had a fivefold increased risk of fever than HIV-negative women (HIV in Obstetrics Group 2004).

The WITS study demonstrated a decline in maternal complications after delivery over time, as management of HIV-infected pregnant women improved. In most settings, both the management and overall health of HIV-infected women has improved dramatically in recent years, and reports of serious complications should be judged in that light. However, complications may also very by setting, even in the developed world, such as among the urban poor in the United States, amongst whom infant mortality is increasing.

Mode of delivery in breastfeeding women

Given that many HIV-positive women in developing countries have limited access to antenatal care, there has been little discussion on the appropriate mode of delivery for these women.

In one study investigating the effects of short treatment courses of AZT plus 3TC in women from South Africa, Uganda and Tanzania, one third of deliveries were by Caesarean section. This mode of delivery was associated with a reduced risk of transmission in women who received treatment during delivery and whose infants were treated for one week, compared with those whose infants were not treated and those who received no treatment whatsoever (Petra Study 2002). For further information, see Short treatment courses in Anti-HIV therapy: Options during pregnancy.

References

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