Prevalence and factors associated with primary and secondary infertility among married or cohabiting women in Zambia: analysis of the 2018 Zambia demographic and health survey

¹Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia, ²Sydney Institute of Infectious Diseases, The University of Sydney, Westmead, New South Wales, Australia, ³Western Sydney Sexual Health Centre, Parramatta, New South Wales, Australia, ⁴Lusaka Apex Medical University, Lusaka, Zambia, ⁵Paediatric Centre of Excellence, University Teaching Hospital, Lusaka, Zambia

^&Corresponding author
Abigail Mulundano, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia

Introduction    

Infertility is increasingly recognized as an important global reproductive health issue, affecting an estimated one in six individuals during their reproductive lifetime [1]. Despite its substantial medical, psychological, and social consequences, infertility remains under-reported and understudied in many low- and middle-income countries (LMICs), particularly in sub-Saharan Africa [2-5]. Variations in definitions, measurement approaches, and access to reproductive health services contribute to wide regional differences in reported infertility prevalence [6,7]. In many African settings, limited availability of nationally representative data has hindered efforts to understand the scale of the problem and to develop evidence-informed reproductive health policies [8,9].

Infertility is commonly classified as primary infertility, defined as never having achieved pregnancy or live birth, and secondary infertility, defined as the inability to conceive following a previous pregnancy [5,10]. Studies from LMICs suggest that secondary infertility is more prevalent than primary infertility, often reflecting a higher burden of preventable reproductive tract infections, unsafe abortion, and limited access to quality obstetric and sexual health services [11,12]. Established factors associated with infertility include increasing age, sexually transmitted infections (STIs), pelvic inflammatory disease, prior pelvic or abdominal surgery, and adverse reproductive health events [11,13]. However, the relative contribution of these factors varies across populations, highlighting the need for country-specific analyses based on representative data.

In Zambia, infertility has received comparatively little research attention, and existing evidence is largely derived from facility-based studies that may not reflect population-level patterns [14]. Understanding the prevalence and factors associated with infertility among women is important for strengthening reproductive health programs, improving access to preventive services, and informing strategies aimed at reducing preventable causes of infertility [1]. Nationally representative datasets such as the Zambia Demographic and Health Survey (ZDHS) provide a valuable opportunity to examine infertility at the population level and to explore sociodemographic and health-related factors associated with its occurrence. Therefore, this study aimed to estimate the prevalence of primary and secondary infertility and to identify factors associated with infertility among married or cohabiting women in Zambia using nationally representative survey data.

Methods     

Study design and setting: this was a cross-sectional study based on secondary analysis of data from the 2018 ZDHS, a nationally representative household survey conducted across all ten provinces of Zambia [15,16]. Zambia is a landlocked country in southern sub-Saharan Africa classified as a low-income setting with diverse ethnic and cultural groups [15,16]. The ZDHS collected demographic, reproductive health, and behavioural data through structured interviews with women of reproductive age using standardised questionnaires [16].

Study population: the source population comprised women who participated in the 2018 ZDHS [16]. The study population included married or cohabiting women aged 18-49 years who were at risk of pregnancy [16]. Women younger than 18 years were excluded because the legal age of consent in Zambia is 18 years. Eligible participants were those who were sexually active, not pregnant, not breastfeeding, not using contraception, and who expressed a desire to have another child [16]. The analysis was restricted to participants with complete data on infertility-related variables. As this was a secondary analysis of an existing nationally representative survey, no additional sample size calculation was performed.

Data collection: data were collected by the ZDHS using standardised interviewer-administered questionnaires covering sociodemographic characteristics, reproductive history, health behaviours, and self-reported medical history. Trained fieldworkers conducted face-to-face interviews using validated DHS survey instruments. For this study, relevant variables were extracted from the women´s dataset, including age, education level, wealth index, place of residence, history of STIs, previous abortion, previous pelvic or abdominal surgery, tobacco use, domestic violence experience, and religious affiliation.

Definitions: the primary outcomes were primary infertility and secondary infertility. Because infertility was not directly measured in the ZDHS, infertility variables were constructed using the World Health Organization definition of failure to achieve pregnancy after a defined period of regular unprotected intercourse [1]. Women were classified as having primary infertility if they had never achieved pregnancy and secondary infertility if they had experienced at least one previous pregnancy but failed to conceive again within the specified reference period. Independent variables were grouped into sociodemographic factors (education level, wealth index, place of residence, and age) and lifestyle or health-related factors (STIs in the past 12 months, previous abortion, pelvic or abdominal surgery, tobacco use, domestic violence, and religion). Categories were regrouped where necessary to ensure analytical consistency.

Statistical analysis: data management and analysis were performed using STATA software version 18 (StataCorp LLC, Texas, USA) [17]. Descriptive statistics were used to summarise participant characteristics, including frequencies and percentages for categorical variables and means with standard deviations for continuous variables. Univariate analyses were conducted to assess associations between independent variables and infertility outcomes using Pearson´s chi-square tests. Variables with P values ≤0.05 in univariable analysis were considered for inclusion in multivariable logistic regression models. Separate multivariable logistic regression analyses were conducted for primary and secondary infertility using a backward stepwise model-building approach. Adjusted odds ratios (aORs) with 95% confidence intervals (CIs) and P values are reported, and statistical significance was defined as P ≤0.05.

Ethical considerations: ethical approval for the 2018 ZDHS was obtained by the implementing agencies in Zambia in collaboration with international partners. Written informed consent was obtained from all survey participants prior to data collection. For this secondary analysis, permission to access the anonymised datasets was obtained from the DHS program, with approval granted on 20^th March, 2024. The study used de-identified publicly available data, and no additional participant contact occurred.

Results     

Participant characteristics: of the 13,682 women interviewed in the 2018 Zambia demographic and health survey, 7,432 met the eligibility criteria and were included in this analysis (Table 1). Overall, 1,909 women (25.7%) were classified as experiencing infertility, including 96 (1.3%) with primary infertility and 1,813 (24.4%) with secondary infertility. The mean age of participants was 31.8 years (±8.3), and most women were aged below 35 years (65.9%). Over half had primary education (51.8%), 44.9% were classified as poor according to the wealth index, and 65.7% resided in rural areas. A history of abortion was reported by 13.0% of women, 5.4% reported a sexually transmitted infection (STI) in the past 12 months, and 5.8% reported previous pelvic or abdominal surgery.

Univariable analysis: the results of the chi-square test analyses are presented in Table 2. Significant differences in infertility status were observed across several sociodemographic and health-related characteristics, including education level, wealth index, place of residence, age group, history of abortion, previous pelvic or abdominal surgery, and STI in the past 12 months (all p <0.001). Tobacco use, domestic violence experience, and religious affiliation were not significantly associated with infertility status in univariable analyses.

Factors associated with primary infertility: results of univariable and multivariable logistic regression analyses examining factors associated with primary infertility are presented in Table 3. In multivariable analysis, women in the middle wealth index had higher odds of primary infertility compared with those classified as poor (aOR: 1.86, 95% CI: 1.02-3.38; p =0.04), and those in the richest wealth index also had increased odds (aOR: 2.45, 95% CI: 1.22-4.92; p =0.01). Reporting an STI in the past 12 months was independently associated with primary infertility (aOR: 2.29, 95% CI: 1.12-4.68; p =0.02). Other variables did not remain statistically significant after adjustment.

Factors associated with secondary infertility: Table 4 presents the univariable and multivariable logistic regression analyses for factors associated with secondary infertility. In multivariable analysis, women aged over 35 years had higher odds of secondary infertility compared with those aged 18-19 years (aOR: 2.87, 95% CI: 1.91-4.32; p <0.001). Secondary infertility was also associated with a secondary level of education (aOR: 1.32, 95% CI: 1.07-1.63; p =0.01), middle wealth index (aOR: 1.27, 95% CI: 1.09-1.48; p =0.002), rich wealth index (aOR: 1.44, 95% CI: 1.21-1.74; p <0.001), previous abortion (aOR: 1.47, 95% CI: 1.27-1.71; p <0.001), previous pelvic or abdominal surgery (aOR: 1.34, 95% CI: 1.08-1.66; p =0.008), and reporting an STI in the past 12 months (aOR: 1.43, 95% CI: 1.14-1.78; p =0.002).

Discussion     

This study aimed to estimate the prevalence of primary and secondary infertility and to identify factors associated with infertility among married or cohabiting women in Zambia using nationally representative survey data. We found that approximately one in four women reported infertility, with secondary infertility accounting for the majority of cases. Reporting a sexually transmitted infection (STI) in the past 12 months and wealth index were associated with primary infertility, while secondary infertility was associated with older age, previous abortion, prior pelvic or abdominal surgery, higher education level, and recent STIs.

The overall prevalence of infertility observed in this study is consistent with estimates reported in several sub-Saharan African settings, where secondary infertility tends to predominate [18-20]. Differences in prevalence estimates across studies may reflect variations in infertility definitions, measurement approaches, and population characteristics [3,20-23]. The relatively low proportion of primary infertility compared with secondary infertility aligns with evidence suggesting that reproductive tract infections and adverse reproductive health events contribute substantially to infertility patterns in LMICs [11,13].

The association between infertility and higher wealth index observed in this analysis has been reported in previous studies examining fertility patterns in LMICs [21]. Women with higher socioeconomic status may delay childbearing due to education or employment opportunities, which can influence fertility outcomes through increasing age at first pregnancy [22,23]. Similarly, the association between increasing age and infertility identified in this study is consistent with established evidence linking advancing age to reduced ovarian reserve and declining fertility potential [24-28]. These findings highlight the importance of considering demographic transitions and changing reproductive behaviours when interpreting infertility patterns.

Secondary infertility was also associated with a history of abortion and prior pelvic or abdominal surgery. Previous studies have suggested that complications related to unsafe abortion or surgical procedures may contribute to reproductive tract scarring or infection, which may affect fertility outcomes [29-34]. Although abortion is legally permitted in Zambia, barriers to access and variations in service quality may influence reproductive health outcomes. Strengthening access to safe reproductive health services and post-procedure care may help address preventable contributors to infertility.

Consistent with existing literature, reporting an STI in the past 12 months was associated with both primary and secondary infertility [35,36]. STIs such as chlamydia and gonorrhoea are known to contribute to tubal damage and pelvic inflammatory disease, which may impair fertility [35,36]. These findings underscore the continued importance of STI prevention, early diagnosis, and effective treatment as part of comprehensive sexual and reproductive health programmes. In contrast, tobacco use and domestic violence were not significantly associated with infertility in this study, which may reflect differences in reporting, measurement limitations, or the relatively small number of women reporting tobacco use [37-41].

This study has several strengths and limitations. The use of nationally representative DHS data allowed for population-level estimates of infertility and enabled comparison with studies from other countries [19,20]. However, infertility was not directly measured in the survey and therefore had to be constructed from available variables, which may introduce misclassification. The cross-sectional design limits causal inference, and all variables were self-reported, potentially leading to recall or reporting bias. Additionally, STIs were assessed only within the past 12 months, which may underestimate lifetime exposure. Despite these limitations, the findings provide important insights into factors associated with infertility among women in Zambia and contribute to the limited population-based evidence from this setting.

Conclusion     

This study found that approximately one in four married or cohabiting women in Zambia experienced infertility, with secondary infertility accounting for the majority of cases. Primary infertility was associated with recent sexually transmitted infections, while secondary infertility was associated with older age, previous abortion, pelvic or abdominal surgery, and having sexually transmitted infections. These findings highlight the importance of strengthening sexual and reproductive health services, including STI prevention and management, to address preventable factors associated with infertility among women in Zambia.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Conception and study design: Abigail Mulundano, Iryna Zablotska, and Kirsten Isla Black; data collection: Abigail Mulundano; data analysis and interpretation: Abigail Mulundano and Iryna Zablotska; manuscript drafting: Abigail Mulundano; manuscript revision: Iryna Zablotska, Catherine Mkandawire Simbao, Chipepo Kankasa, Lackson Kasonka, and Kirsten Isla Black; guarantor of the study: Kirsten Isla Black. All the authors read and approved the final version of this manuscript.

Acknowledgments     

We acknowledge the University of Sydney, Faculty of Medicine and Health, for their unwavering support.

Tables     

Table 1: selected characteristics of married/partnered women aged 18-49 years (N=7432, 2018 Zambia demographic and health survey)

Table 2: comparison of fertile women and those with primary and secondary infertility: Zambia demographic and health survey 2018-2019 (N=7,432)

Table 3: relationship between selected characteristics of partnered women and primary infertility: Zambia demographic and health survey 2018-2019 (N=5,619)

Table 4: relationship between selected characteristics of women and secondary infertility: Zambia demographic and health survey 2018-2019 (N=7,301)

References