Unintended pregnancy, which includes both mistimed and unwanted pregnancies, is a global social and health challenge. Worldwide, 38% of pregnancies are unintended (that is, some 80 million pregnancies annually). In sub-Saharan Africa, unintended pregnancy accounts for more than a quarter of the 40 million pregnancies that occur annually. Unintended pregnancies increase health and economic risks for children, women, men and families. Research indicates that unintentional pregnancy is a key risk factor for adverse pregnancy and maternal outcomes, including mortality and morbidity associated with unsafe induced abortions [1–3] Unintended pregnancy has also been linked to low use of appropriate maternal health care [2, 4]; [5, 6]. Unintended pregnancy is also a major cause of unsafe abortion [1–3, 6].

As in most of Africa, the prevalence of unintended pregnancy in Kenya continues to be high. In Adetunji's [7] study of eight sub-Saharan African countries, Kenya recorded the highest proportion of unintended childbearing. In the 2003, the Kenya Demographic and Health Survey (KDHS) showed that nearly 50% of unmarried women aged 15–19 and 45% of the married women reported their current pregnancies as mistimed or unwanted [8]. The 2008–09 KDHS showed that 43% (26% mistimed and 17% unwanted) of married women in Kenya reported their current pregnancies as unintended [9]. Unintended pregnancy is one of the most critical factors contributing to schoolgirl drop out in Kenya. Up to 13,000 Kenyan girls drop out of school every year as a result of unintended pregnancy [10] In addition, unsafe pregnancy termination contributes immensely to maternal mortality which currently estimated at 488 deaths per 100 000 live births [9].

Studies have shown a wide range of correlates of unintended pregnancy. Unintended pregnancies mostly arise as a result of nonuse or incorrect use of contraceptives, or a noticeable contraceptive failure [6, 7, 11]. Unintended pregnancies have also been shown to be strongly associated with maternal age and number of previous births [2, 7, 11–13]. A prospective study in 2 governorates of Upper Egypt revealed that the majority of women never used contraception, and unintended pregnancy was more prevalent in this category of women compared to those who had ever contraception used [14].

In Chile, women aged less than 25 and of low socioeconomic status were more likely, than their peers living in households of better socioeconomic status, to have unplanned pregnancies [15]. In Harare, a significant association was found between unintended pregnancy and age, with women aged 19 years and below or 35 years and above having a higher risk of unintended pregnancy [16]. Similar results have been reported in several other studies. Young women have higher likelihood of inconsistent or nonuse of effective family planning methods than older women and have greater risk to have mistimed than intended pregnancy [17–19]. Urban women, furthermore, are less likely than rural women to have more children than that which they regard as ideal. Research from different countries also indicate that women with better education levels were less likely than those with less education levels to have more children than that which they regard as ideal. Moreover, the higher education and the better socioeconomic status a woman had, and then it is less likely for her to have an unplanned pregnancy [2, 7, 11–13].

Existing literature on unintended pregnancy in Kenya has addressed its socio-demographic correlates, national prevalence, implications for maternal and child health and care-seeking, and repeatability [5, 7, 20]. These studies have relied largely on national large-scale or localized facility-based surveys. Little is therefore known about the prevalence and determinants of pregnancy among women from diverse socio-economic and livelihoods, particularly in urban areas of Kenya. The current study addresses the prevalence and the determinants of unintended pregnancy among women in slum and non-slum settlements of Nairobi.

Following rapid urban growth under enormous economic constraints, an increasing proportion of Kenyans now live in cities. However, urbanization in Kenya has produced critical geographic concentrations characterized by both prosperity and poverty. Cities, deeply divided along socio-economic lines, have thus emerged all over the country. Currently, high-rent neighborhoods characterized by affluence exist next to slums noted for their squalor and impoverished livelihoods. Generally, livelihood conditions vary clearly between these zones, often translating into objective differences in health outcomes [21].

Poor urban settlement contexts set limits on the ability of women and men to safeguard their sexual and reproductive health, control their fertility, and implement their fertility aspirations [21, 22]. Essentially, these settlements are characterized by extreme poverty and poor livelihood conditions, limited access to family planning services, illiteracy, sexual violence, and lack of access to quality health care, including ante and post-natal care services. They present particularly interesting and fertile locations for unintended pregnancy and related behavior [21].

This study addressed the prevalence, socio-economic and demographic correlates of unintended pregnancy among slum and non-slum women in Nairobi. About 24% of the women reported an unintended pregnancy. The 2008–09 KDHS indicates that 43% of Kenyan women and 29.4% of women in Nairobi Province in particular reported their most recent pregnancies to be unintended. Judging by these figures, the incidence of unintended pregnancy among women in the study was slightly lower than the national and provincial averages. While many factors can explain the comparatively lower incidence of unintended pregnancy in the study communities, the growing availability of family planning products in the study communities needs to be highlighted. The study areas have also been the targets of aggressive family planning campaigns in recent times [23].

In the study, education and household wealth were surprisingly not strongly associated with unintended pregnancy. This is contrary to many other studies on the correlates of unintended pregnancy [24, 25]. However, judging by results of the logistic regression, it is difficult to entirely dismiss the influence of income and educational levels on unintended pregnancies among the women we studied. This is because employment status was a strong predictor of unintended pregnancy. Women in formal employment were also 55% (p < 0.01) less likely to experience unintended pregnancy compared to unemployed women or students. Formal employment is related in critically important ways to earning capacity, educational levels, and social networks [26–29]. Women in formal employment tend to earn more, have higher levels of reproductive health knowledge and participate in social networks that support family planning and reduced fertility [29–34].

Further, similar to previous work from Kenya, we found that young and unmarried women in the study were, irrespective of their educational attainment and household wealth status, at high risk of experiencing unintended pregnancy [21, 22, 35, 36]. Research in Kenya generally, and in the specific areas that we covered indicates that young people have limited access to quality sexual and reproductive health information, including knowledge on contraception [5, 6, 19, 21, 22, 36]. In addition to the unaffordability of family planning products and services to many girls, several hospitals and clinics in Kenya where family products and services – mainly, oral contraceptives, injectables, implants, male condoms, IUDs and, very rarely, vasectomy – are subsidized or provided free of charge regularly experience stock outs and a dearth of qualified providers [37]. Stigma, inadequate sexuality information and cultural pressure to appear sexually chaste and inexperienced also hinder utilization of family planning services among young girls and unmarried girls [38]. Most young girls in Kenya also rely on parents, equally uninformed peers, and popular media for information on sexual maturation, pregnancy and sexuality, who often do not provide them correct and timely information, exposing them to sexual and reproductive health risks including unintended pregnancies [21, 36, 39, 40].

Interestingly too, ethnicity had statistically significant effect on unintended pregnancy. In both settlements, being Luo or Luhya was associated with a higher likelihood of experienced unintended pregnancy compared to being a Kikuyu. Due largely to their growing access to higher education, greater participation in paid employment and widespread use of contraceptives, the Kikuyu as a whole has continued to experience steadydeclines in fertility in the recent past. On the other hand, while there is evidence of higher levels of pronatalism among the Luyha and Luo than among the Kikuyu, there is also research suggesting that women from the former ethnic groups are among the poorest and least empowered in Kenya [41–44]. The rates of unintended pregnancies from the Provinces where the Luo and Luyha traditional reside, e.g., Western and Nyanza Provinces are also among the highest in Kenya [5, 19]. Higher levels of unintended pregnancy among the Luo and Luyha in the study may relate to their lower empowerment status, poorer socio-economic status and more limited access to family planning products [21, 45, 46]. Compared to Kikuyu women, more Luo and Luhya women in Kenya currently survive as dependents of men in relationships that hinder their power to protect themselves from unintended pregnancies and sexually transmitted infections [21, 47, 48]. The poorer socio-cultural and economic status of Luo and Luyha women finds expression, among other things, in the ideology of patrilineal inheritance, male-biased property rights, virilocalism and male ownership of children. For instance, among the Luo, upon the death of a husband, his widow(s) is also eventually claimed as property by brothers-in-laws or other male relatives of the deceased husband [21]. On the other hand, in the Kikuyu culture, children and the responsibility of catering for them are primarily perceived as women’s, not men’s. Kikuyu women may thus be much keener in looking for ways to avoid pregnancies that they are not well-prepared for [49, 50].

The study found a high prevalence of unintended pregnancy among the study population. Young and unmarried women, irrespective of their educational attainment and household wealth status, had a higher likelihood of experiencing unintended pregnancy. Except for the results on educational attainments and household wealth, our findings compared with the results reported in the literature.

The study results are critical and raise the need for programs and strategies to improve access to contraceptive services and related education, socio-economic status and information and communication particularly among the young and unmarried women. Increased availability and accessibility of family planning services is crucial to reducing unintended pregnancy among the study population. Concerted and coordinated multi-sectoral efforts are key to expanding access and uptake of family planning services. Increased access should be accompanied with improvement in the quality of care and availability of information about effective utilization of family planning methods.