BMC Public Health 2008, 8:309 http://www.biomedcentral.com/1471-2458/8/309 prevention programmes are less likely to be pregnant and equally less likely to contract HIV infection. As such, sen- tinel surveillance of pregnant women would over-esti- mate HIV prevalence in the general female population. On the other hand, there is some evidence that HIV-1 could impair fertility [3,4]. If HIV infected women are less likely to be pregnant because of impairment of their fertil- ity by the HIV virus, the use of sentinel surveillance would under-estimate the HIV prevalence. Research comparing ANC estimates of HIV prevalence with HIV prevalence from population-based studies has shown that ANC figures closely estimate the actual popu- lation prevalence [5-7]. However, the findings have not been consistent [8]. Saphonn et al (2002) reported that although the prevalence of HIV in ANC was good for monitoring trends, it over-estimated HIV prevalence in rural Cambodia [9]. On the contrary, Changalucha et al (2002) reported that the prevalence of HIV from ANC underestimated community HIV prevalence in Tanzania [10]. Grassly, et al (2006) reviewed studies that have been carried out in different countries and compared estimates from ANC sentinel surveillance with population based estimates [11]. They found that in 12 out of 15 countries, HIV prevalence from ANC surveillance closely estimated the actual population prevalence. However, prevalence from ANC over-estimated community prevalence in Kenya and Rwanda, but underestimated the community prevalence in Zambia. Assuming that prevalence from ANC surveillance is representative of pregnant women, and that errors resulting from laboratory testing are mini- mal, one major explanation of inaccuracies in the esti- mates is the differences in the fertility rates between HIV positive and negative women. The accuracy of HIV esti- mates from ANC also depends on the contraceptive prev- alence and ANC coverage. Improved methods for estimating HIV prevalence such as population-based surveys can provide useful information on HIV prevalence levels and distribution, and improve HIV estimates at national and regional levels [12]. How- ever, surveys may be costly especially when there are fre- quent and nation-wide. Research on ANC sentinel surveillance has mainly been focused on the role of behavioural data in ANC surveil- lance [13], uses of prevalence data [14], coverage [15], assessing the trends of HIV prevalence [16-18], compari- son between HIV prevalence from ANC and community prevalence [9,10] and methods of adjustment of estimates from ANC surveillance [11,19]. In addition some research has addressed the differences in fertility according to HIV status [2,20]. Glynn et al (2000) reported that the birth interval was reduced in HIV positive multiparous women compared to HIV-negative multiparous women in three African cities, namely Yaounde (Cameroon), Kisumu (Kenya) and Ndola (Zambia) [20]. Using sentinel data of pregnant women, the prevalence of HIV in Cameroon rose from 0.5% in 1987 to 10.8% in 2000 and then dropped to 7.3% in 2002 (Ministry of Pub- lic Health, 2001 and 2003) [21]. A population-based sur- vey conducted in 2004 estimated the overall adult HIV prevalence in Cameroon to be 5.5% [22]. It is not clear whether this represents a true decrease in the prevalence of HIV or an artifact due to the differences in the two methods of data collection. Knowledge about the accu- racy of sentinel prevalence as a proxy for national HIV prevalence is indispensable especially in a country facing rapid changes in the HIV prevalence. Differential preva- lence of HIV in pregnant and non-pregnant women has been reported to be significantly associated with age, mar- ital status, parity, schooling, and contraceptive use [23]. The purpose of our study was to compare the fertility rates of HIV-infected and HIV-uninfected women using popu- lation-based data in order to make recommendations on the appropriate adjustments when using sentinel data in designing and evaluating HIV prevention programmes in Cameroon. Methods Design This study is a cross-sectional, population-based survey that uses data from the 2004 Cameroon Demographic and Health Survey (DHS) [22]. Women of reproductive age (15 to 49 years) were interviewed about their past and current reproductive history and tested for HIV after obtaining informed consent. Ethical approval was sought from the Cameroon Ministry of Health prior to the origi- nal survey [22]. Population and sampling The survey used a two stage cluster sampling technique. The sample frame was a list of all Enumeration Areas (clusters) established by a General Census of Population and Housing in 2003. The first stage involved selecting 466 clusters (primary sampling units) with a probability proportional to the size, the size being the number of households in the cluster. The second stage involved the systematic sampling of households from the selected clus- ters. All women aged 15 to 49 years in the selected house- holds were interviewed. The details of the study methods have been published elsewhere [22]. The current report included only sexually active women aged 15 to 49 years. Laboratory analysis The HIV status was screened by direct ELISA test (Gen- screen Plus Version, BioRad Laboratories) and confirmed by a competitive ELISA test (Wellcozyme HIV-1 recom- Page 2 of 7 (page number not for citation purposes)