This study analyzed fertility behavior data of 1,020 women born during the 1965–1969 cohort based on cross sectional-retrospective data in Zambia. Our results show that the average CFS was 6.7 (95% CI: 6.5–6.9) and that mean age at first marriage and first birth were 18.3 (95% CI: 18.0–18.5) and 18.9 (95% CI: 18.7–19.1) respectively. About 11% of women with CFS above 6 children married before age 15 and 5% had their first birth within the same age range. Higher CFS of 6 or more children were concentrated among women whose age at first marriage and birth was between 15 and 18 years old (40.7 and 39.8% respectively). Women marrying at younger ages and having their first birth at younger ages were more likely to have higher CFS than compatriots that initiated both marriage and childbearing at or after age 22.
The main strength of this study is it followed a cohort of women who had or were about to complete their reproductive cycle and collected fertility information about this group in a manner that provided grounds for exploring determinant. The study also controlled for socioeconomic factors to effectively discern associations. Furthermore, the use of probability sampling in the collection of this data gives this study sufficient leverage to generalize findings to the entire 1965–1969 cohort in Zambia. However, our study also presents some limitations. As are all surveys that depend on retrospective responses, self-reported data may introduce biases such as social desirability bias, non-response bias, recall bias, interviewer bias etc., even in the presence of exceptionally trained enumerators and rigorous probing to encourage accuracy of reporting [50–52]. Women, especially in rural areas, might report children they have adopted (could be for a sister who died, husband children from an earlier marriage, etc.,) as their own due social desirability. People in traditional settings have a tendency not to count children that die shortly after birth as live birth. The primary limitation of the cross-sectional study design is that because the exposure and outcome are simultaneously assessed, there is generally no evidence of a temporal relationship between exposure and outcome [52], [53]. However, since there exist a considerable amount of time lag between getting married and having children, a temporal relationship between age at first marriage, age at first birth and CFS can be established.
Understanding changes in CFS is an important indicator of the anticipated future in lifetime fertility behavior of women. Factors that influence these changes become cornerstones for predicting fertility behavior and determining population growth. This study found a CFS of 6.7 children for the 1965–1969 birth cohort based on retrospective data analysis. This finding is consistent with results from the 2013-14 ZDHS that also found the average number of children ever born was 6.7 for women nearing the end of their childbearing cycle and 7.3 for those currently married, alluding the difference in the two measures to lower fertility among the young unmarried women [9] in the former index. This CFS is higher than the current TFR for most African countries including Zambia itself [28], [29]. TFR in Zambia reduced from 6.1 in 1992, 5.9 in 2010, 5.3 in 2014 to 4.7 in 2018 [13], [25–27]. The CFS is the major determinant of the average household size that remains high in most African countries [54]. The household size in Zambia is high at 5.1 persons (urban 4.8 and rural 5.4) [10] relative to the TFR of 4.7 children.
Our study further found that women from the 1965–1969 cohort married early (mean = 18.3; CI: 18.0-18.5) and that by the end of their reproductive life, 68.3% of them had birthed 6 children or more. With changes in reproductive behaviors overtime, this rate is expected to be lower for future cohorts. In fact, a study conducted in Malawi found that older cohorts have higher fertility than younger ones [55]. As expected, marriage plays a crucial role in shaping the course of fertility, especially in the developing world [28]. The timing of marriage predominantly regulates how many children will be born since marriage is the only institution that sanctions reproduction. Over half (51.2%; CI: 48.1–54.3) of the women from our study married between age 15 and 18 and a substantial number (13.5% CI:11.5–15.8) married at ages below 15 years. Our analyses reveal that almost two-thirds (64.7%) of women from this cohort were married off when they were still underage exposing them to a long period of the risk of childbearing. Fifty-one percent of women with 6 or more children got married by age 18. Studies have shown that women that marry early, start childbearing early, remain at risk of childbearing for longer periods of times and have poor health outcomes than their counterparts who marry later [56], [57]. The timing of marriage in Zambia is affected by a myriad of socioeconomic factors, including education, wealth, social status and cultural responsibility that influence CFS. This study found that the cohort under investigation generally had more children, but the probability of having fewer children was higher for urban women than rural women. To put this into perspective, one study investigated how household economic hard times affect the time of marrying off their children especially in Africa where payment for marriage, whether in cash or kind, is widespread. They found that parents tactfully selected the time for their children’s marriage depending on household economic instability thus affecting age at marriage as the payments for marriage constitute a vital source for “consumption smoothing” for the bride’s family [58].
A woman’s age at first birth have grave implications for a roller coaster of life events such as education, work-life and completed family size. The results of this study found that the mean age at first birth for the cohort was 0.6 years higher than for marriage and 1.9 years higher than for sex debut. This finding suggests that the birth of the first child, in most instances, was preceded by sexual debut and then marriage. Similar analysis but for 43 countries found that the mean age at first birth was greater than the mean age at first marriage, which was also greater than the mean age at first sex for all regions [28]. A similar study conducted in Pakistan found that the hazards of birth increased in the first two years following marriage and their after declined [59].
Another significant aspect that affects CFS is education of women. We found that women with no education and primary education (52% and 39.7% respectively) tended to have more children than those with secondary (3%) and tertiary education (4.7%). Even though noticeable progress has been attained, rural areas of sub-Saharan Africa still display low education levels for women [28], [60]. Thus, the education atmosphere is not favorable to any meaningful change in CFS for rural women in the region [55], [57]. Not only does education delay age at first birth, it also enhances the power of choice among women such that their consumption patterns enable them to live healthy and pursue healthy choices in child rearing [28]. Our findings show that in all the models, education attainment was inversely related to CFS. The lower the education level attained, the higher the CFS; but age at first marriage and first birth are positively related to education level attained. This, however, is expected as women who attend secondary and tertiary education are selective, such that the timing at which events occur intersect and compete with schooling age; much more in post primary than primary 49,50. Numerous reasons have been advanced that cause the inverse relationship between a woman’s education and fertility that include but not limited to superior autonomy among women, exposure to new gender norms and childbearing practices, improvement in information acquiring useful to women’s health and their offspring. Women with more education are also selective in partner choice, have higher need for wealth and understand the costs that accrue or are forgone in timing of reproductive events.
Relatedly, women that reported having never used contraception were 6.9 times (95% CI:3.3–8.5) (Model 2) more likely to have 1–3 children than 6 or more children compared to participants that have ever used contraceptive. This is an expected result because the variable “Ever used contraception” does not measure frequency of contraceptive use during the active childbearing years nor does it measure current use for those still bearing children. The best way of understanding the effect of contraceptive use on CFS is to retrospectively investigate the frequency of and reasons for contraceptive use for women at the height of their childbearing career. Education has also been cited as a source of instruments necessary for obtaining information that enhances women and girls’ ability of comprehending and learning information regarding contraceptive use and the benefits of smaller families. It could be because education is not as widespread in rural areas that women there exhibited higher fertility behaviors than their urban counterparts. In terms of household wealth, our results indicate that the distribution of women by household wealth did not vary much. The range was 18.2% (95%CI: 159-20-7) for lowest to 22.5% (95% CI: 19.9–25.1). Within household wealth classes, the highest proportions were recorded among women with 6 or more children. Table 4 model 2 shows that the higher the household wealth the less the risk of having 1–3 children relative to 6 or more children. The relationship between household wealth and CFS when CFS is 4–5 children was not statistically significant. This outcome could be as a result of measuring household wealth as current and not during their childbearing years or at the beginning of their childbearing period. Retrospective studies have this limitation in linking duration measures to point estimates.