Low rates of MTCT in UK and Ireland

29 August 2008. Related: Pregnancy, CROI 15 (Retrovirus) 2008.

Polly Clayden, HIV i-Base

A paper authored by Claire Townsend and co-workers published in the May 11, 2008 edition of AIDS reported very low rates of mother-to-child transmission (MTCT) of HIV in UK and Ireland, 2000-2006. [1]

Findings from this analysis were first reported in a poster at the 15th Conference on Retroviruses and Opportunistic Infections in February and summarised in the March/April issue of HTB. [2,3]

This national surveillance study found an overall transmission rate of 1.2% (61/5151, 95% CI: 0.9-1.5%). The rate was lower in 2003-2006, 1% (938/3695) than in 2000-2002, 1.6% (923/1456), p=0.069. The transmission rate for women who received antiretrovirals for at least the last 14 days of pregnancy was 0.8% (40/4864, 95% CI: 0.6-1.1%), regardless of type of antiretroviral treatment or prophylaxis or mode of delivery.

In multivariate analysis (n=4892) including receipt of antiretrovirals, mode of delivery, gestational age and sex, the authors found receiving no antiretrovirals, AOR: 9.08, p=0.001 was the greatest risk factor for transmission. Girls were more likely to be infected than boys, AOR:1.91, p=0.023.

Preterm delivery (<32 weeks) was also a significant risk factor, AOR: 3.55, p=0.01. However, the authors noted that of the seven women with infected premature infants, three were received no antiretrovirals and four for <3 weeks (range: 1-19 days) and six had vaginal deliveries. Preterm delivery was not a significant risk factor for women receiving HAART, AOR:1.32, 95% CI: 0.3-5.82, p=0.714.

There was a non-significant overall 1.8 fold increased risk of transmission associated with vaginal delivery compared to elective Caesarean section, AOR: 1.82, p=0.076. In this cohort information on whether vaginal deliveries were planned or unplanned was available for 69.1% (775/1122) of women. After adjusting for receipt of antiretrovirals, gestational age and sex, unplanned vaginal delivery was associated with a significantly increased transmission risk, AOR: 4.16, 95%CI: 1.66-10.41, p=0.002 but planned delivery was not, AOR:1.56, 95% CI: 0.65-3.72, p=0.319.

The MTCT rate for women receiving HAART was 1.0% (40/4120). The rate did not differ significantly when HAART contained an NNRTI, 90.9% (18/1959), a PI, 1.1% (20/1795), p=0.625, both 0.8% 92/258) or neither 0% (0/108), p=0.847.

When the authors compared NNRTI and PI regimens, after adjusting for mode of delivery, sex and viral load (gestational age was excluded from this analysis, because, as noted earlier, it was not a significant risk factor for women receiving HAART in this cohort), AOR:1.31, 95% CI: 0.62-2.76, p=0.482, there was no difference in MTCT rates between the two types of regimens.

Already receiving HAART at conception showed a modest advantage, AOR: 0.18, 95% CI: 0.02-1.33, p=0.093. Women who transmitted and initiated HAART in pregnancy (n=34) began treatment later than those who did not, with median gestational age 30.1 weeks (IQR: 27.4-28.7 weeks) for those who transmitted vs. 25.9 weeks (IQR: 22.4-28.7 weeks) for those who did not, p=0.001.

The authors noted that each additional week of treatment gave a 10% reduction in transmission risk, AOR: 0.09, 95% CI; 0.84-0.97, p=0.007 (after adjusting for viral load closest to delivery, mode of delivery and sex).

For women receiving HAART there was no difference between transmission rates with elective Caesarean (0.7%, 17/2286) or planned vaginal delivery (4/559, AOR: 1.24, 95% CI: 0.34-4.52), p=0.746.

Viral load was undetectable in 58.7% (1135/1934) of women having elective Caesareans and 79.0% (417/528) of those having planned vaginal deliveries, p=0.001.

There were 3/2117 transmissions reported from women receiving HAART with undetectable viral load (0.1%, 95% CI: 0.0-0.4%). Two were delivered by elective Caesarean (0.2%, 2/1135) and one by planned vaginal delivery p=0.001. One positive infant born by elective Caesarean section and one by planned delivery had positive PCR results within 72 hours of birth suggesting transmission in utero.

Transmission rates were higher in women receiving HAART, with both emergency Caesareans and unplanned vaginal deliveries, p=0.027 and 0.019 respectively.

Eighteen other women had positive infants despite HAART and either planned delivery or elective Caesarean section. For 10 women the authors found an association with either: short duration of treatment, high viral load near delivery (range 8500-285,000) or adherence problems. Six women had low but detectable viral load (</=50 and <1000 copies/mL and two women received HAART for at least a month but there were no viral load data.

For women receiving AZT prophylaxis and elective caesarean section, the transmission rate was 0% (0/464, 95% CI: 0-0.8%).

Overall 3/638 (0.5%, 95% CI: 0.1-1.4%) infants were born to women receiving AZT prophylaxis. All three women received AZT for less than 1 month, had detectable viral load (range 474-3000 copies/mL) and had vaginal deliveries.

The authors conclude: “Our findings suggest that offering HIV-infected women choices about HIV treatment and mode of delivery according to current guidelines has led to very low rates of MTCT.”

References:

1. Townsend CL, Cortina-Borja M, Peckham CS et al. Low rates of mother-to-child transmission of HIV following effective pregnancy interventions in the United Kingdom and Ireland, 2000-2006. AIDS 2008, 22:973-981.
2. Townsend C, Cortina-Borja M, C Peckham C et al. Very low risk of MTCT in women on HAART who achieve viral suppression: The UK and Ireland, 2000 to 2006. 15th CROI. February 2008, Boston. Poster abstract 653.
3. See: HIV Treatment Bulletin, March/April 2008.
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