The study was aimed to assess the prevalence and associated factors of PTB among women who gave birth in the study area. In this study, the prevalence of PTB was 11.41%. This study is in line with studies conducted in Africa (11.9%) (5), North America (10.6%) (5), Tanzania (14.2%) (33), and Nigeria 12 % (9). A similar finding was also obtained from studies at Axum, Tigray region (13.3%) (23), and Debretabor town, Ethiopia (12.8%) (15). This similarity between the present study and the previous studies in Axum and Debretabor may be due to various related levels of socioeconomic status and lifestyle of the respondents since all are low-income and middle-income countries.
The result of this study is lower than studies conducted in Kenya (18.3%) (8) and Jimma, Ethiopia (25.9%) (13). This discrepancy might be because multiple pregnancies were not included in this study since this may result in an over-distended uterus and can cause spontaneous preterm labor and delivery. The reason for this variation also might be due to the difference in the health-seeking behavior of the study participants and methodological differences. However, the finding in this study is higher than studies carried out in Iran (5.1%) (7), Sweden (5.03%) (10), and Gondar town, Ethiopia (4.4%) (12). This variation could be due to the difference in the study time, inclusion and exclusion criteria, quality of health services, and socio-demographic characteristics.
The odds of giving PTB were higher among mothers who had preeclampsia, maternal age less than 20 years, PROM, chronic medical illness during pregnancy, and history of stillbirth.
Our findings revealed that the likelihood of PTB among mothers in the age group less than 20 years of age was eight times higher compared to the mother’s age group of 20–30 years. This is consistent with a systematic review and meta-analysis conducted in East Africa (34). The study is also supported by studies done in Canada (35) and Ethiopia (22). This might be due to the age of mothers increases, their health-seeking behavior, and knowledge about pregnancy-related health problems will also be raised. Moreover, young women are more prone to many risk behaviors like alcohol consumption and less adherence to advice and counseling given by their health professionals compared to elder women(22).
Our study revealed that mothers who had preeclampsia had a 5 times increased risk of PTB than those who had no preeclampsia. This result is similar to a study carried out in Southern India (36), Kenya (8), Nigeria (37), Addis Ababa (18), Debremarkos (32), and a study conducted in public hospitals in Sidama zone, Southeast Ethiopia(19). This might be due to the complications of hypertension disease that can cause vascular damage to the placenta or decrease the uteroplacental blood flow. This induces oxytocin receptors and results in intrauterine growth restriction that causes preterm labor and delivery.
We found that mothers with PROM had four times 4 times more to give preterm birth than those with no PROM. This is consistent with the study done in Ghana (20), Nigeria (37), Kenya (8), Debretabor(15), and Sidama, Southeast Ethiopia (19). This could be because PROM raised fetal plasma interleukin-6 leading that the fetal response will activate preterm labor spontaneously (38). Furthermore, this might be explained by the influence of the membrane rupturing on uterine contraction. The research evidence claims that some endogenous uterotonic hormones are released when the membrane ruptures and these hormones, in turn, induce uterine contractions, triggering PTB.
Moreover, this study revealed that mothers who were exposed to chronic medical illness (HIV, anemia, chronic kidney disease, and cardiac disease) during pregnancy had 5-fold higher odds of PTB compared to those who were not exposed to any medical illness. This finding is supported by studies carried out in Jimma, Southwest Ethiopia(13), and Debremarkose, northwest Ethiopia (32), and a systematic review and meta-analysis of East Africa (34). This might be due to medical disorders during or before pregnancy affects the placenta and the membrane, in turn, reduces the placental flow of oxygen and nutrients to the developing fetus in utero, and, thus, increases the risk of preterm birth (39).
In our study, a mother who had a history of stillbirth had 3 times higher odds of PTB compared to those mothers who did not have a history of stillbirth. This study is in agreement with studies done in Sidama, Southeast Ethiopia(19), and a study conducted in Jimma, Southwest Ethiopia(13). This might be due to the recurrence of stillbirth in some women who initiate preterm labor in the preceding pregnancy.
Limitations of the Study
Being a cross-sectional study does not confirm a definitive cause-and-effect relationship. Since the study was hospital-based, it may not clearly show the real picture of PTB in the area.