Discussion
Our study site is a tertiary hospital that is appointed by ministry of health, as an official referral center for congenital anomalies in Oman. Over a decade period of time, there were 147563 obstetric patients seen in the Ultrasound and Fetal Medicine units, of which 1502 cases found antenatally to have major congenital anomalies. The study population is quite young, >10% were diabetic, have high consanguinity and a significant previous history of MCA with one third perinatal mortality rate, and majority from the capital area and the coastal region. The average antenatal prevalence of congenital anomalies over 10 years was 10.1 per 1000 pregnancies. The most common anomalies seen in this study were those of the nervous system (29.2%), followed by cardiothoracic system. Over the 10 years, the trend of recorded anomalies was fluctuating, recording the highest in 2018 were 11.3 anomalies per 1000 pregnancies and lowest in 2011 (5.2 per 1000 pregnancies).
In the present study, the prevalence of major congenital anomalies was lower compared to two studies were conducted in Oman, the first one as an abstract that reported rate of 16.8 per 1000 pregnancies (24). This study was conducted for a period of one year, in a single center which receives only selected cases from limited regions of the country. The second study was an abstract as well, which reported rate of 6.7 %, also it was a one-year study representing one regional hospital which receives cases of that region only (25). However, our cases are from all over the country and done over many years to provide a better overall rate of major congenital anomalies.
Many studies from different regions or countries report different anomaly rates, which might be attributed to the diversity in study methods, classifications of birth defects and times of studies (7, 17, 19, 22, 26-28). In addition, differences in cultural, genetic, socio-economic elements among studied populations.
Several studies demonstrated an increase rate of birth defects associated with advanced maternal age, especially in females older than 35 years old (17, 26). In our study sample, advanced maternal age was one of the common coexisting factors found in our cohort.
In Middle Eastern countries, the prevalence of consanguinity is known to be high. Besides that, important association between consanguinity among couples and increased rate of congenital anomalies has been reported in previous studies (23, 29-33). In our study sample, 22% of mothers were married to their first cousins. Almost consistent with a study was conducted in Oman, which showed about 24.1% of studied couples married from their first cousins (34).
The burden of congenital anomalies in high risk pregnancies is known to be high (35). Our study described females with bad obstetric history like repeated miscarriages, previous congenital anomalies and perinatal deaths, which might play a role in the development of birth defects in future offspring’s, as reported by Sunitha etal. They concluded in her study that females with high risk pregnancy and bad obstetric history found to have double rate (11%) of congenital anomalies, compared to general population (6%) (35).
Many epidemiologic studies have illustrated the association between pregestational diabetes (particularly DM type2) and increased risk of specific birth defects in offspring’s (36). In our study, the most common coexisting maternal risk was pregnancy with diabetes. This emphasizes the importance of pre-pregnancy counselling and planning with aim of optimal glycemic control for women with preexisting diabetics before they conceive. While the general population risk for having a baby with an MCA is one to three percent, that for a woman who has pregestational diabetes mellitus is three to six times as great. Fetal organogenesis takes place from the fifth to the eighth post-menstrual weeks. A body of evidence suggests that maternal hyperglycemia early in gestation is either contributory to fetal teratogenesis or is a surrogate marker for the causative agent of MCAs in infants of diabetic mothers (37).
As illustrated in figure 1 , what can be noticed that, the number of cases diagnosed with congenital anomalies was increasing throughout the years and it is likely due to advancement in ultrasound scan technology, with the utilization of skilled and professional sonographers. Hence, we anticipate an increase in early detection of major congenital anomalies in the coming decade.
Prevalence studies are very beneficial in identifying the baseline rates of congenital anomalies and changes over time. Which is crucial in public health planning and establishment of preventative measures. This study highlights the prevalent nature of antenatal fetal anomalies over a decade of time. Nevertheless, we may have remarkably under-estimated the real incidence of congenital anomalies in the general population. As our hospital is a tertiary health organization, mostly complicated cases are referred, on the other hand, uncomplicated cases may have been followed in other peripheral hospitals.
Early referrals and antenatal diagnoses of major anomalies is crucial for the proper counselling of parents, timely fetal or neonatal intervention, elective termination of pregnancy if needed (38). In addition to that, it helps in planning the delivery in suitable health facility and future prevention. In this study, cases where firstly referred and seen between 10 to 40 weeks of gestation (mean gestational age 27.4 weeks). One case referred early at 10 weeks of gestation, for multiparous women found to have Anencephaly and body stalk anomaly. Early diagnoses enabled timey counselling and elective termination of pregnancy (23, 39) .
There are 11 main geographical areas (regions) in Oman, figure 3 (Provincial map of the Sultanate of Oman). Muscat region is the capital city and around 50% of the population lives there. Al Batinah region contains the largest amount of provenance and was split to Al Batinah North and South. The study showed that majority of referred cases (42.9%) were from Muscat and Al Batinah, Costal, regions (37.15% cases), which is expected due to the higher density of population in these areas.
The most common anomalies seen in this study were those of the nervous system (29.2%), followed by cardiothoracic system. Similar findings were identified in unpublished data from maternal child health unit at ministry of health. Neural tube defects were the most common types of anomalies seen in Nervous system. The dominance and high frequency of neural tube defects in this study was also reported in previous studies in same geographical areas as in Oman Saudi Arabia (7, 23, 29), UAE (40-43), Iran (26, 44, 45), Pakistan (28, 46, 47) and India (17, 35, 48-50). Besides, this finding was similar to studies reported by Sawardekar Kiran in 2005, a decade review of major congenital anomalies in Nizwa, Interior provenance, in Oman (51). On the other hand, some countries have reported a decrease in reported incidence of neural tube defects, due to the active intervention in promoting and implement preventative measures, like folic acid fortification in food and supplementation in preconception period (52).
Various randomized trials with other observational studies have illustrated that maternal intake of folic acid with or without multivitamin supplements in preconception period and in early pregnancy could reduce the occurrence and recurrence of neural tube defects (53). In our setting, we need to emphasize more in implementing preventative measures, like food fortification, pre-pregnancy supplementation with effective preconception counselling to emphasize the importance of folic acid and multivitamins intake before planning for pregnancy.
Many increasing evidences showing the link between preconception maternal environmental exposures like tobacco smoke, outdoor air pollution, water with disinfection byproducts, outdoor air pollution and pesticides and elevated risk of congenital anomalies (52, 54). In addition, modified maternal lifestyle habits can predispose to the development of congenital anomalies (55). In the present study, 32% of mothers described to have coexisting maternal factors, the most common one was diabetes in pregnancy (8.8%). This modifiable risk can be significantly reduced by effective preconception counselling and aiming for a controlled glycemic index before conception.
Congenital anomalies are one of the leading causes of perinatal morbidities and mortalities (52). The perinatal mortality rate in our study was 32.6% among fetus with major congenital anomalies. This was almost similar to the unpublished data at MOH (almost 30 %) and 34.9% reported in Saudi Arabia (7, 23, 29). It is important to have further future studies, assessing factors which can affect outcome and survival in neonates born with major birth defects.