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.