HIV prevalence among young pregnant women

Export Indicator

The proportion of young pregnant women testing positive for HIV during sentinel surveillance at selected antenatal clinics.
What it measures

In most countries, young women who attend ANCs are a reasonably representative sample of young women in the general population. Young women who are pregnant have had unprotected sex at some time in the preceding 10 months, and potentially, therefore, have been sexually exposed to HIV infection. On average they are not a group characterized by other high-risk behaviour. Participation bias is relatively low in this sample because HIV testing is carried out, either anonymously with blood that is routinely taken from all pregnant women for other routine tests, or as a routine offer as part of the PMTCT programme. Most HIV infections among young women have been recently acquired. Trends in HIV prevalence in this group may therefore reflect trends in the incidence of new HIV infections.

Rationale
Numerator

The number of young pregnant women who, while attending antenatal clinics (ANCs), test positive for HIV infection in sentinel surveillance.

Denominator

All young pregnant women who are tested for HIV infection while attending ANCs in sentinel surveillance.

Calculation
Method of measurement

HIV prevalence is estimated from testing of blood samples that are routinely taken from pregnant women of all ages at sentinel ANCs. The quality of the data depends on the structure of the surveillance system. An ideal sentinel surveillance system would include clinics chosen to reflect a country’s urban, rural, ethnic and other socio-geographical divisions. However, in most countries ANC clinics that participate in sentinel surveillance are not nationally representative, with ANC’s in urban areas overrepresented. The methods used for surveillance should be the same at all sites. The indicator should be reported as separate percentages for the groups 15–19, 20–24 and 15–24 years. It should also be reported by parity for primigravidas and multigravidas for 15-24 year olds. If the sample is large enough the results can be disaggregated by both age and parity. Parity is important because prevalence among women having their first pregnancy provides a better estimate of incidence. The median prevalence of contributing clinics should be reported, together with the number of clinics contributing data, the number of women tested and the number testing positive for HIV infection. The data should be presented for the capital city, other urban areas and rural areas.

Measurement frequency
Disaggregation

Age group: 15 years - 19 years, 15 years - 24 years, 20 years - 24 years

Education: N/A

Gender: N/A

Geographic location: N/A

Pregnancy status: N/A

Sector: N/A

Target: N/A

Time period: N/A

Type of orphan: N/A

Vulnerability status: N/A

Explanation of the numerator
Explanation of the denominator
Strengths and weaknesses

In countries where the epidemic is driven heterosexually this indicator gives a fairly good idea of relatively recent  rends in HIV infection nationwide. It is less reliable as an indicator of overall epidemic trends in areas where the bulk of HIV infection remains confined to subpopulations with especially high-risk behaviour. In this circumstance it is a useful way of monitoring whether HIV infection is spreading beyond these subpopulations. In order to interpret changes in the prevalence of HIV infection at ANCs it is important to isolate real changes in the proportion of young women who are infected with HIV from artefacts of the surveillance system. The HIV prevalence observed among young women attending ANCs may change for a number of reasons not directly connected with the true prevalence of HIV infection among young women in the general population. Changes that affect the number of young women who become pregnant, the proportion of those who seek antenatal care, and the stage of pregnancy at which women first visit an ANC could all affect the HIV prevalence observed in ANCs. Some of these changes, such as an increase in the age at first sex, may also affect the incidence of new HIV infections among young women. For these reasons, trends in the prevalence of HIV infection among young pregnant women should be interpreted carefully. When trends are being monitored the sample composition is very important. The representativeness of the clinic sample is only as good as the data on which the sampling frame was based. Accurate information about the size and location of clinics allows this to be treated with more confidence. Interpretation is easier if the same sample of clinics is used in several rounds of surveillance. When changes are considered in the clinics that constitute the ANC surveillance system, clinics for which past data exist should be retained in the sample, so as to enable trend analysis. HIV prevalence among young pregnant women can be used to estimate HIV prevalence among young women in the general population. Software is available for developing the adjustments necessary to make the data representative of the general population. However, detail on this estimation is beyond the scope of the present guide.

Further information