Risk factors for the incidence of major structural birth defects
Many studies have been conducted to determine the association of various risk factors with the incidence of birth defects. For example, in Kenya, Tanzania and Iran the number of malformed babies appeared to increase with increasing maternal age especially from 35 years and above [5-7]. The same is true in our study; Maternal age was significantly associated with birth defect. Women above 35 years old were around five times more likely to have neonates with birth defect as compared to those women who are in the age group of 20-35 years old. However, a research done in Addis Ababa and Saudi Arabia [8, 9] showed that there is no significance difference between cases and controls regarding maternal age for occurrence of birth defects.
In rural areas of Gabon structural birth defects were rare or absent as compared to the number recorded in urban areas . In this study neonates born from women living in an urban area were about six times more likely to develop birth defect as compared to those neonates born from women who live in a rural setting and the odds of women to have a newborn with the birth defect was around four times higher among women living in Dega as compared to women whose primary address was in woyina Dega. This was supported by research on epidemiology of birth defects based on a birth defect surveillance system from 2005 to 2014 in Hunan Province, China.
This may be due to diet diversification habits and non-fat diet in rural areas of Ethiopia as has been shown its effect in an animal model study  and a greater level of air pollution in urban areas 
Studies conducted in a variety of settings around the world have observed a significant association between maternal fever and birth defects consistent with our findings [6, 14, 15]. A population-based case control study done in Shanxi province Northern China on risk factors for neural tube defects found that a history of fever during the periconceptional period was associated with almost a threefold increase in risk for neural tube defects, which persisted even after controlling for other covariates[16, 17]. This were in congruent with our study on which mothers who had history of fever during pregnancy were around three times more likely to have neonates with birth defect even after adjusting for other factors.
As reported from northern Ghana the use of herbal medicines by pregnant women poses a potential danger to the fetus and development of 70% birth defects of unknown etiology . In our study intake of herbal medicine during pregnancy was significantly associated with major structural birth defects. Those women who took herbal medicine during pregnancy were around eleven times more likely to get a new born suffering from birth defect compared to women who didn’t take herbal medicine while pregnant. In Ethiopia pregnant women used herbal medicine in the first trimester of pregnancy  in which organogenesis and birth defect occur .
The 2011 Ethiopia Demographic and Health Survey found that 45% of women and 53% of men reported drinking alcohol at some point in their lives . The association of alcohol drinking during and before early pregnancy and birth defect was reported as having significant association [8, 22, 23].
In our study Maternal history of alcohol intake during pregnancy was found to be significantly associated with birth defect. Women who took alcohol during their pregnancy were around thirteen times more likely to have newborns with birth defect as compared to those women who didn’t take alcohol during their pregnancy.
Both moderate and high levels of alcohol intake during early pregnancy may result in alterations in growth and morphogenesis of the fetus. Microcephaly, short palpebral fissures, epicanthal folds, maxillary hypoplasia, short nose, thin upper lip, abnormal palmar creases, joint anomalies, and congenital heart disease are also present in most infants .
Protective factors for the incidence of major structural birth defects
Counselling has a positive effect on a range of health outcomes like prevention of birth defects . Physician counseling can reduce risk of medication-induced birth defects  and increase intake of folic acid before conception  so can reduce incidence of birth defect as explained by many researches.
Similar to above report counselling for pregnancy preparation in our study was found protective for the incidence of birth defect. Women who didn’t get counselling for pregnancy preparation were about five times more likely to have neonates with the birth defect as compared to women who got counselling for pregnancy preparation.
Nearly one-half of pregnancies are unintended so preconception care should be considered an integral part of primary care for women of reproductive age. Provide counselling regarding common issues in preconception care like family planning, screening and treatment for infectious diseases, updating appropriate immunizations, and reviewing medications for teratogenic effects can prevent poor birth outcomes including birth defect .
Researches in different setup showed that women who took folic acid were less likely to have babies with birth defects as compared to those who did not take folic acid during and before early pregnancy[6, 28-34].
Intake of folic acid supplementation can reduces nearly 75% of the rate of neural tube defects. It is recommended to take 4 to 5 mg of folic acid daily starting three months before conception and continuing until 12 weeks post conception[36, 37].
In our study women who didn’t get folic acid supplementation at or before pregnancy were about seven times more likely to have neonates with birth defect as compared to those women who had been supplemented with folic acid during and before pregnancy which is consistent with other studies that have shown folic acid supplementation is protective against birth defects[37-41].
Folate acts as a cofactor for enzymes involved in DNA and RNA biosynthesis. Interruption of DNA biosynthesis or methylation reactions could prevent the proper closure of the neural tube. Such inhibition could be caused by simple deficiency of either folic acid or vitamin B12 .
In this study, there is no statistically significant association between season of birth and the absence or presence of birth defects. But the data should be collected and analyzed based on the season of conception rather than the season of birth or termination. This was the main limitation of the study.