The TFR for the three years preceding the survey was estimated at 3.4 children per woman which was below the national and regional average (10). TFR in the study area showed a continues declining from 3.9 children per woman in 2012 (28). Thus, the trend shows that the total-fertility rate target stipulated in the Ethiopian population policy achieved before the expected period which couldn’t be achieved at national level (10, 31). The result also depicted Age Specific Fertility Rate in the study area reached its peak in the age group of 25–29 and falls slowly with advancing age. However, studies conducted in Ethiopia in 1990s and before showed that women in age group with the highest fertility level was 20–24 (15, 31, 32) which shows the shifting of the peak ages in ASFR or the postponement of births to the later ages that may be attributed to the increasing of age at first marriage and birth.
The multivariate results showed that the residence, age, occupation of women, child death experience, marriage and wealth index could have been responsible for the current fertility in the study area. According to the result, marriage had a positive and strong association with fertility. The level of recent fertility was more than fivefold higher among currently married women than their unmarried, consistent with a study from Addis Ababa city (33). This indicates that premarital fertility is very minimal in the study area in which birth is highly attached with marital union as birth out of wedlock is socially unacceptable in Ethiopia (10, 34). The prevailing decline in the proportion of currently married women may contribute to the reduction of the recent fertility (9, 10).
The other predictor of fertility is current age of women. In this study fertility was significantly higher among women of age group 25–34 but significantly declining after age 34 compared to women of 15–24 age group which was fully mediated by marriage. This result was confirmed by previous studies that suggested the causes related to behavioral and biological reasons. Regarding the behavioral reasons, it was suggested that fertility decline occurred among women in the later reproductive ages because of the fact that women took deliberate steps to limit subsequent childbearing once they had borne the desired number of children. Women will begin to have all of the children they desire immediately after marriage and will continue to have births until they achieve their target family size and then will actively prevent the birth of additional children (35). It would be because of these individual decisions that produced the fertility decline in old age groups. On the other hand, in biological reasons, the ability of older women to get pregnant is naturally becoming low, the embryo implanting ability and survival start declining gradually after 30 years of age, but by more than two thirds after 40 years (36, 37).
Residence was one of the variables that significantly associated with fertility. The study depicted those urban women had a lower chance of having children compared to their rural counterparts. The influence of urban residence on recent fertility was fully mediated by marriage. This difference may be due to the fact that women in urban areas enter into unions at relatively older ages and an increasing proportion of single women with very low premarital fertility (38). This shift in union formation to later age is commonly attributed to women's increasing levels of education, greater participation in wage employment and the development of alternative roles for women outside marriage and motherhood (39).
The types of occupations in which women were engaged also affected the fertility in the study area. Employed women and those who looked for job had lower level of fertility compared to housewives in that the effect on fertility was fully mediated by marriage. Employed women were possibly educated and were likely to marry at later ages. Employment influences on women’s marital decisions as it tends to lead women to appreciating singlehood and cohabitation over marriage (40). Nowadays, studies reported that women's rising employment levels have increased their economic independence and hence have greatly reduced the desirability of marriage and consequently have fewer children (41). On the other hand, job seekers usually postpone their marriage which in turn influence the level of fertility. Studies indicated that there has been a growing sentiment that women's involvement in and attachment to the paid labor force before marriage has become part of their gender freedom (42, 43). The result also revealed that students had lower level of fertility compared to housewives. Girls who stay in school longer have a direct influence to lower their probability of having child (44). The effect for the students was also partially mediated by marriage in that the chance of girls to marry is low until they completed their education. Studies mentioned that it was to avoid the challenges of getting involved in their own relationship such as to dedicate time to marriage and household responsibilities that may distract from their studies which in turn reduce the level of fertility (45).
Women who had large ideal number of children had a positive association with fertility which has a direct effect with absence of influence through marriage. This is similar to other studies where the desire to have lower children usually tending for decline in fertility (46). History of child death among the married women in this study was found to have a positive association with fertility but fully mediated through marriage. Women who had a child-death experience were likely to have a higher number of children than those who had no such experience. Similar studies indicated that high child mortality causes high fertility through the insurance and replacement effect, married women were exposed to a higher risk of uncontrolled fertility as number of children who died increased (6, 46, 47).
Household wealth status was found to have an important influence on women’s fertility. Contrary to the findings of many studies (48, 49), fertility in this study was significantly higher among women with better wealth quintile compared to women with the poorest wealth status, the risk of fertility progressively increases with the level of household wealth. Nowadays, in low-income countries, poor people have the same desired fertility and even they tended to have lower number of births as compared to their wealthy compatriots, consistent with a study from Tanzania (50) and Ethiopia (38, 51). This might be attributed to the increasing severe economic difficulties that may initiate women not to give birth. The effect of wealth of poorer and richest category was full mediated through marriage. For the middle and richer wealth quintile, their effect on fertility was partially mediated through marriage.
Contrary to most studies on fertility determinants (47, 48, 52), the result of this study revealed that education and media exposure did not show any association with fertility. It could be supposed that differences among individuals in different categories in fertility behavior may be diminishing due to improved communication links among educated and uneducated, and the entire societies that may help to have similar information about the benefit of having desired number of children in a household. This may be due to the deployment of health extension workers since 2003 in each Kebele (53).
The results of many studies (20, 23, 25) revealed that the prevailing contraceptive use has showed a significant and negative association with fertility. However, in the present study, current contraceptive use was only marginally significant (P = 0.078). There was no evidence that current contraceptive use has an effect for the recent fertility decline. Similar findings were documented in Amhara and other regions of the country (6, 33, 54). It could be supposed that the absence of the effect of contraception may be due to low level of contraceptive prevalence rate (CPR) that might not be at the level (CPR = 17%) of influencing the current fertility and might be due to high discontinuation rate in the study area.
Women were asked whether they can decide on major household expenses that might indicate whether they can be able to pass a decision on the number of children they wish to have and the use of contraceptive methods they prefer at any time. However, the result showed that the variable had no any association with fertility. Respondents were also asked whether household experienced food shortage in five years preceding the survey that may indirectly showed the household economic status and risk to susceptibility. However, the result showed that the variable had no any association with fertility.
The use of Dabat HDSSs database to recruit study participants and administration of the questionnaire by the surveillance site supervisors and data collectors could be mentioned as strengths for the current study. The surveillance staffs knew study participants for a long time and this also built trust on the participants side to provide reliable information. As a limitation, this study did not interview men, in cultures where males tend to dominate decisions, about their fertility preferences and behavior assuming detailed information was more readily and accurately obtained from females, and males and females have similar attitudes toward a number of key issues that may affect fertility behavior.