Determinants and impact of joint decision-making on contraceptive use among women in union in Nairobi’s urban informal settlements: a repeated cross-sectional analysis and agent-based microsimulation using the Nairobi Urban Health and Demographic Surveillance System

Objectives To estimate the prevalence and determinants of joint decision-making on contraceptive use among women in union in Nairobi’s informal settlements, and to project the contribution of different decision-making patterns to the modern contraceptive prevalence rate (mCPR) over time. Design Analysis of repeated cross-sectional surveillance data combined with an agent-based microsimulation (Thanzi la Onse-Nairobi Urban Health and Demographic Surveillance System (NUHDSS). Determinants of joint decision-making were examined using multivariable logistic regression, and model performance was assessed using the likelihood ratio test, the Hosmer-Lemeshow goodness-of-fit test, McFadden pseudo R 2 and the area under the receiver operating characteristic curve. The microsimulation projected mCPR from 2012 to 2040 under joint, woman-only and spouse-only decision-making scenarios. Setting Two urban informal settlements, Korogocho and Viwandani, in Nairobi, Kenya, covered by the NUHDSS, 2012–2015. Participants 2085 women of reproductive age (15–49 years) who were in union, defined as married or living with a male partner, with complete data on the decision-making outcome. Primary and secondary outcome measures The primary outcome was joint decision-making on contraceptive use (woman and partner deciding together vs the woman alone or the partner alone). The secondary outcome was the projected mCPR among women in union from 2012 to 2040 under joint, woman-only and spouse-only decision-making scenarios. Results Joint decision-making prevalence was 63.7% (95% CI 61.6 to 65.8). In the adjusted model, the odds of joint decision-making were higher in male-headed households (AOR 1.53, 95% CI 1.11 to 2.10, p=0.009), among residents of Viwandani (AOR 1.30, 95% CI 1.04 to 1.64, p=0.024), among women who desired more than five children (AOR 2.27, 95% CI 1.02 to 5.12, p=0.045) and among unemployed women (AOR 1.36, 95% CI 1.09 to 1.69, p=0.006), and lower among women who did not want another child (AOR 0.63, 95% CI 0.48 to 0.82, p<0.001), were undecided about childbearing (AOR 0.62, 95% CI 0.43 to 0.87, p=0.006) or had not discussed family size with their partner (AOR 0.39, 95% CI 0.31 to 0.51, p<0.001). In the microsimulation, the contribution of joint decision-making to mCPR among women in union rose from 40% in 2012 to 52% in 2040, exceeding the contributions of woman-only (13% to 18%) and spouse-only (about 1% to 0.5%) decision-making. Conclusions Joint decision-making was associated with higher modern contraceptive use among women in union in Nairobi’s informal settlements, and the microsimulation suggests it may contribute substantially to mCPR over time. Because the design is cross-sectional, these associations should not be interpreted as causal. Programmes that strengthen couple communication, particularly in male-headed households and among unemployed women or couples with undiscussed or discordant fertility preferences, may support progress toward national family planning targets.