Association between plural legal systems and sexual and reproductive health outcomes for women and girls in northern Nigeria: a regional and state-level ecological study from 1990 to 2013

Background: Plural legal systems allow various sources of law to govern simultaneously. Plural legal systems have long been part of Nigerian civil law in 12 northern states, nine of which have added criminal law under Sharia Law jurisdiction since 2000. Disparities in education and wealth within Nigeria are reflected in disparate regional health outcomes, with southern Nigeria often faring better than northern Nigeria with regard to maternal and child, and sexual and reproductive health (SRH). Discriminatory legal systems can reinforce and worsen pre-existing health disparities in SRH by limiting women's civil and socioeconomic freedoms. Consequently, we expect to find a relation between adverse customary law (ie, religious or traditional law) and negative SRH outcomes in northern Nigeria. Methods: SRH outcomes for women and girls were compiled from five Nigerian Demographic and Health Surveys (DHS) in 1990, 1999, 2003, 2008, and 2013. Selected indicators included, but were not limited to, fertility (eg, total fertility rate, age of first marriage), SRH (eg, contraception use, knowledge of HIV/AIDS), and maternal health (eg, antenatal care, delivery location). A time-trend analysis was done to consider the percentage change in indicator outcomes for five regions over time. We did the same time trend analysis with state-level data available for 2008 and 2013. For 2013 data, t-tests were done between states with customary and religious laws and those without. A secondary analysis was done with northern states only to account for differences in baseline education and wealth levels between northern and southern states. Education level is hypothesised to be a moderator of the relationship between living in a state with customary and religious laws and laws that impede access to SRH services and poor health outcomes. Simple linear regression was carried out to investigate the relationship between current use of contraception among married women and living in a state with customary and religious laws and laws that impede access to sexual and reproductive health services. To test for mediation, we conducted a multivariable linear regression adding education level as another predictor of contraception use. Findings: Our time trend analysis suggests regions with customary and religious laws and laws that impede access to SRH services see fewer improvements in women's health outcomes over time, whereas outcomes for women's health in regions without such laws see marked improvements. For example, the percentage of married women using any type of contraceptive method in southeastern states went from 8·8% in 1990 to 29·0% in 2013, while the percentage increased from 1·2% to 4·3% in the northwest. States with customary and religious laws saw on average a 0·28% change increase in current use of contraceptive method by married women, whereas states without such laws saw a 5·3% change increase from 2008 to 2013. In 2013, women in states with customary and religious laws had significantly lower levels of HIV knowledge (p=0·05), received less antenatal care (p=0·001), and had higher fertility rates (p<0·001). When limiting the analysis to northern states, women in those with customary and religious laws had higher fertility rates (p=0·003), lower use of contraceptive methods (p<0·001), and participated less in their own health-care decisions (p<0·001). The regression on current use of contraception and living in a state with customary and religious laws showed a significant relationship between the two variables (R2=0·55, p<0·0001]. When testing for mediation by education, the overall equation was still significant (R2=0·71, p<0·0001] but the relationship was weaker in this analysis (β=2·74, t=0·43, p=0·67) compared to the direct relationship (β=–22·71, t=–6·65, p