Mother-to-child HIV transmission at all-time low in the UK but around two-thirds of reported cases involve women diagnosed after delivery

Factors such as uncertain immigration status, housing problems and intimate partner violence are common among women who pass on HIV to their infants in the UK, according to the results of an audit published in HIV Medicine

The results showed that perinatal HIV infection in the UK is at its lowest-ever level, with 108 cases reported between 2006 and 2013. Approximately two-thirds of cases involved women who did not find out they were HIV positive until after they gave birth, and adverse circumstances during pregnancy were reported in 53% of cases.

“Our audit demonstrated that at least half of women were experiencing adverse social circumstances, and in nearly a third of cases multiple factors were reported,” comment the investigators. “At least one key factor likely to have contributed directly to HIV transmission was identified in the vast majority of cases. The most common were decline of an HIV test in pregnancy (accounting for nearly half of undiagnosed women) and seroconversion (around a quarter).”



The period of time from conception up to birth.

mother-to-child transmission (MTCT)

Transmission of HIV from a mother to her unborn child in the womb or during birth, or to infants via breast milk. Also known as vertical transmission.


The transition period from infection with HIV to the detectable presence of HIV antibodies in the blood. When seroconversion occurs (usually within a few weeks of infection), the result of an HIV antibody test changes from HIV negative to HIV positive. Seroconversion may be accompanied with flu-like symptoms.



Relating to the period around the time of birth. Perinatal transmission is when HIV is passed on during pregnancy, childbirth or breastfeeding. People with perinatally-acquired HIV have been living with HIV since birth or infancy.

person years

In a study “100 person years of follow-up” could mean that information was collected on 100 people for one year, or on 50 people for two years each, or on ten people over ten years. In practice, each person’s duration of follow-up is likely to be different.

There are approximately 35,000 women living with HIV in the UK and each year around 1200 become pregnant. Antenatal HIV screening, obstetric care and management of HIV during pregnancy have all contributed to a decline in the rate of vertical transmission of HIV in the UK from 2% in 2000-01 to 0.3% in 2012-14.

There are very few infections in infants of mothers known to have HIV, but some do occur in infants whose mothers were undiagnosed at the time of delivery. This is a matter of considerable concern as the risk of serious illness and death in infants with perinatally acquired HIV (PHIV) is very high unless antiretroviral therapy (ART) is started promptly.

An audit of PHIV in England in 2002-05 showed that communication failures, suboptimal ART and adverse social circumstances were involved in cases of mother-to-child HIV transmission. Investigators repeated this exercise for children with PHIV born in the UK between 2006 and 2013. The aim was to see if there were any common trends and factors between cases and how infections might be prevented in the future.

An expert panel reviewed anonymised case summaries to identify factors contributing to cases of PHIV. Eight common factors emerged:

  • Woman declined antenatal HIV tests
  • Seroconversion during pregnancy
  • Problems with engagement with care or ART adherence
  • Postnatal transmission probably due to undisclosed breastfeeding
  • Presenting late for antenatal care
  • Transferring antenatal care provider
  • Pre-term delivery curtailed duration of ART meaning viral load remained detectable
  • Problems with the antenatal test result, such as result not being reported.

There were approximately 9200 live births to HIV-positive mothers during the study period. A total of 41 cases of HIV transmission from diagnosed mothers to infants were identified and there were a further 67 cases involving mothers whose HIV infection was only diagnosed after delivery.

The mothers had a median age of 29 years and 90% were born abroad. The number of infants diagnosed with PHIV fell from 31 in 2006 to a single reported case in 2013.

A single factor contributing to transmission was identified in 62% of cases, two factors in 22% of cases, three in 5% of cases and one case had four or more factors. It was not possible to establish factors in 10% of cases.

Reporting clinicians were aware of at least one adverse social factor in 53% of women already diagnosed with HIV. These included uncertain immigration status (29%), housing problems (29%), intimate partner violence (10%), involvement of social services (20%), mental health issues (20%), lack of fluency in English (20%) and drug/alcohol abuse (10%).

Detailed analysis of the 41 infants born to previously diagnosed mothers showed that over half were probably infected in the womb, 20% during delivery and 20% in the postnatal period, probably due to undisclosed breastfeeding.

The most common contributing factor (n = 14) in these cases was lack of engagement with care or poor adherence to ART. Late presentation to antenatal care was documented in eleven cases, postnatal transmission (probably due to breastfeeding) in seven cases, pre-term delivery in three cases and late diagnosis in pregnancy in two cases.

Common factors contributing to transmission involving undiagnosed mothers included declining the offer of an HIV test (28 of 67) and seroconversion during pregnancy (23 of 67).

Overall, eight children died during the study period: one from complications following pre-term delivery, the other seven of HIV-related causes. The overall mortality rate was 1.3 per 100 person-years but was 2.2 per 100 person-years for children born to undiagnosed mothers.

“The MTCT [mother-to-child transmission] rate in the UK in diagnosed women is at an all-time low and reports of PHIV in infants born to undiagnosed women have also declined,” conclude the investigators. “This audit provides important insights into contemporary cases of HIV transmission in the UK that could inform future policy and practice, with areas of clinical practice requiring improvement identified.”

Priorities include:

  • Earlier engagement with antenatal care
  • Reducing HIV incidence during pregnancy
  • Improving adherence to ART and engagement with specialist HIV and other care
  • Addressing health and social inequalities.

Peters H et al. National audit of perinatal HIV infections in the UK, 2006-13: what lessons can be learnt? HIV Med, 19: 280-89, 2018.