Vertical transmission rate below 0.3% among women living with HIV in the UK

Polly Clayden, HIV i-Base

Vertical HIV transmission in the UK remains very low, according to data presented at HIV Glasgow 2022. Changes in the characteristics of women living with HIV accessing antenatal care have implications for service provision and need continued monitoring. [1]

The low transmission rate reflects both the antenatal screening programme – that includes HIV testing and has an uptake rate of 99% – as well as effective clinical management of HIV in pregnancy.

HIV population level surveillance has been in place for over 30 years in the UK and enables the monitoring of trends. The oral presentation showed recent trends in characteristics and outcomes of pregnancies among women living with HIV, using data from the NHS Integrated Screening Outcomes Surveillance Service (ISOSS).

ISOSS is conducted as part of the NHS Infectious Diseases in Pregnancy Screening Programme, UCL Great Ormond Street Institute of Child Health. All pregnancies in women living with HIV in the UK, their infants and any children living with HIV are reported to ISOSS (this changed to England only in 2020).

The dataset and analyses covered pregnancies in women diagnosed before delivery with estimated date of delivery during 2014–2019 and reported by 31 December 2021.

There were 5858 pregnancies among 3353 women during the surveillance period. The annual number decreased from approximately 1100 in 2014–2015 to 800–900 in 2018–2019. The proportion of women diagnosed during pregnancy declined over time.

From 2014–2019 the median age at estimated date of delivery was 34 years (IQR: 30 to 38) – this increased over time.

There were several shifts in maternal characteristics in 2014–2015 compared to 2018–2019. All were statistically significant (p<0.001):

  • Maternal age >40 years increased from 12.5% to 19.1%
  • Pregnancies in women born in sub-Saharan Africa decreased from 72.0% to 64.1%
  • Pregnancies in women born in Eastern Europe increased from 4.3% to 6.9%
  • Pregnancies in women with vertically-acquired HIV increased from 1.7% to 3.7%

Maternal diagnosis before pregnancy increased from 86.8% in 2014–2015 to 90.6% in 2018–2019. And the percentage on ART at conception among this group increased from 77.8% to 89.0% during the same time periods. (Both p<0.001).

The overall proportion of pregnancies conceived on ART increased from 67.2% in 2014–2015 to 81.0% in 2018–2019 (p<0.001).

Women diagnosed in pregnancy started ART increasingly earlier: from 19 weeks’ gestation (IQR 16 to 23) in 2014– 2015 to 16 weeks (14 to 20) in 2018–2019.

The proportion of women with first antenatal CD4 count >500 cells/mm3 increased from 51.2% in 2014–2015 to 58.5% in 2018–2019 (p=0.001).

Over the surveillance period, there were 5117 (87.1%) live births and 44 (0.75%) still births. Overall, 92.1% of deliveries were to women with viral load <50 copies/mL. For those on ART from conception, this proportion was 95.5%. There were no statistically significant differences between to two time periods.

Vaginal deliveries increased from 44.3% in 2014–2015 to 47.4% in 2018–2019. And emergency caesareans decreased from 26.9% to 22.3%, respectively. (Both p<0.001). The preterm delivery rate remained approximately 12%.

Supported breastfeeding cases – in line with BHIVA guidelines – increased from 1.5% in 2014–2015 to 5.8% in 2018–2019 (p<0.001).

The vertical transmission rate for infants born to diagnosed women (in England) declined steadily from 2.86% reported in 2000–2001 to a plateau of approximately 0.3% since 2012.

Two related posters ISOSS showed results from further analyses of characteristics and outcomes of pregnancies among women with vertically-acquired HIV and with supported breastfeeding in the UK. [2,3]

Women with vertically-acquired HIV are an emerging cohort in the UK. This dataset and analysis was from pregnancies with known outcomes reported to ISOSS between 2006 and 2021 (no pregnancies were reported in this population before 2006).

There were 17,478 pregnancies overall, of which 202 (1.6%) were among women with vertically-acquired HIV. There was a 10-fold increase in the proportion of pregnancies in with vertically-acquired HIV – from 0.3% in 2006–2009 to 3.5% in 2018–2021. In the same surveillance period, there was a decrease in the proportion of pregnancies among women with heterosexually-acquired HIV (p<0.001).

Just over half (54%) of women with vertically-acquired HIV were African-born compared with 74% for women with heterosexually-acquired HIV; 37% were UK-born compared with 15%, respectively (p<0.001).

The median age at delivery among women with vertically-acquired HIV was 24 years of age compared with 33 years for those with heterosexually-acquired HIV.

Fewer women with vertically-acquired HIV had viral load less than 50 copies/mL at delivery compared with those with heterosexually-acquired HIV: 55% and 87% vs 74% and 93% during 2006–2010 and 2016–2021, respectively (p<0.05). ART at conception increased significantly over time among both groups of women as did earlier antenatal visits.

Of the 202 pregnancies among women with vertically-acquired HIV, there were: 170 (84%) live births, 10 (5%) miscarriages, 18 (9%) terminations, and 4 (2%) stillbirths.

Preterm birth and low birth weight were more common among women with vertically-acquired HIV (both <0.001). Of infants with complete follow up, 1/150 (0.66%) was diagnosed with HIV.

The number of women choosing supported breastfeeding in the UK is increasing. Although it remains comparatively small. BHIVA pregnancy guidelines recommend formula feeding but state that women with undetectable viral load and good adherence wishing to breastfeed may be supported to do so.

ISOSS has collected data on supported breastfeeding since 2012. Among 8526 live births there were 267 (3.1%) reports of intention to breastfeed and/or breastfeeding. Reports have increased 4-fold from less than 10 per year in 2012–2014 to 40 to 50 per year in 2019–2020. At the time of analysis, 203 women were confirmed to have breastfed (using linked paediatric reports).

Of 96 women with this information recorded, 77 were known to have had monthly mother and infant testing in line with BHIVA guidelines. About a quarter of this group had issues for mother/infant testing.

The median duration of breastfeeding among mother/infants who had stopped breastfeeding at time analysis (150/203) was 56 days. Of those reported to have stopped, 71% of infants had a negative18–24 month antibody test, with no transmissions to date. The HIV status for the remainder could not yet be determined based on 18–24 month testing as the majority of these infants are still in follow up (23%), discharged before antibody testing (3%) or lost to follow up (3%).


These outcomes for the approximately 900 pregnancies among women with HIV in the UK are reassuring – with the current vertical transmission rate below 0.3%.

Among the growing population of women with vertically-acquired HIV, as well as those with heterosexually-acquired HIV, all markers have improved over time. Though numbers are very small, there may be a slightly elevated risk of transmission among the vertically-acquired group. The authors note that further work is needed to understand why fewer women with vertically-acquired HIV have undetectable viral load at delivery – to help to optimise outcomes in this cohort.

Supported breastfeeding is expected to continue to slowly increase in the UK. There are no vertical transmissions to date but a few are lost-to-follow-up and some are still being followed.

Importantly, among vertical transmissions occurring in the UK, a number are attributed to undisclosed and supported breastfeeding by women with undetectable viral load. So this option needs to be very carefully discussed and managed.

This excellent surveillance programme continues to inform future guidance and optimal clinical management of pregnant women living with HIV and their infants.


  1. Peters H et al. Trends in maternal characteristics and pregnancy outcomes among women living with HIV in the UK: 2014 to 2019. HIV Glasgow 2022. 23–26 October 2022. Oral abstract MO46.
  2. Peters H et al. Pregnancy characteristics and outcomes of women with vertically-acquired HIV in the UK. HIV Glasgow 2022. 23–26 October 2022. Poster abstract P001.
  3. Francis K et al. Supported breastfeeding among women with diagnosed HIV in the UK – the current picture. HIV Glasgow 2022. 23–26 October 2022. Poster abstract P041.

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