In five Arab countries, mothers who were infected with COVID-19 before or during pregnancy had more than two-fold higher odds of having a child with more severe CL/P. Fear of COVID-19 and other maternal stressors during the pandemic were not significantly associated with the severity of CL/P. To our knowledge, this is the first study to assess the impact of COVID-19 on the severity of CL/P controlling for the effects of other known risk factors associated with CL/P. Our study provides evidence suggesting that the effect of COVID-19 may occur at a much earlier stage of human development by impacting the normal growth and development of infants independently from known cleft determinants. The findings shed light on an effect of COVID-19 that has not been explored till now, thus filling a knowledge gap. The high odds and relatively narrow confidence interval suggest a strong association between COVID-19 infection and CL/P severity that is precisely estimated. The observed association seems to indicate a pathophysiological pathway rather than a psychosomatic route since the association with fear of COVID-19 infection was not significant. The study findings and the questions they raise call for future studies conducted in other countries where contextual factors may modify the observed association and for investigation of the pathways through which the observed effect occurs.
Only fewer studies assessed the determinants of CL/P severity. Two studies found a positive association between the severity of CL/P presentation and older parental age [25] as well as family history of NSOFC [26]. The etiology of NSOFC could be genetic, environmental, or as a result of genetic-environmental interactions [27]. Most previous studies focused on the occurrence of NSOFCs [28], with a case-control study reporting no association between maternal COVID-19 infection and CL/P occurrence in infants [29]. The field of epigenetics shows how the environment affect the way genes work with evidence showing effects on tooth development [30], oral cancer, craniofacial syndromes as well as caries and periodontal disease [31]. Infections may switch on and off specific genes responsible for different processes [31] thereby modify their action. For example, infection with Mycobacterium tuberculosis affects the IL-12B gene which weakens the immunity [32] and may favor the occurrence or progress of different diseases. Epigenetic modulation may be one mechanism through which COVID-19 infection before or in early pregnancy moderates the action of genes responsible for NSOFCs, increasing cleft severity. CL/P development has been previously associated with other infections during early pregnancy such as influenza [33], HIV and human papillomavirus infection yet results remain inconclusive [33, 34]. Infections that cross the placental barrier can lead to subsequent fetal infections [35]. COVID-19 infected placentas showed common features like maternal and fetal vascular malperfusion and cellular inflammation [36] which may restrict fetal growth, delay development, and possibly lead to stillbirth [37]. Further studies are needed to elucidate the mechanism by which COVID-19 increases the severity of NSOFCs.
In addition, we found higher odds of greater CL/P severity with exposure to life stressful events and fear of COVID-19 although the associations showed weaker effect sizes and were not significant. Previous studies showed that maternal exposure to stress during early pregnancy was associated with CL/P in infants [15] and before pregnancy stress exposure was associated with two-fold higher risk of NSOFC development [38]. Only one of these studies, however, considered the impact of COVID-19 which might have overshadowed the impact of these factors in the present study. Stress may increase the risk of NSOFC through activating the sympathetic nervous system to increase blood profusion leading to placental hypoperfusion which negatively impacts fetal development [39] and through higher level of cortisol, a primary stress hormone, which has a teratogenic effect on the developing fetus, resulting in craniofacial abnormalities [40].
Furthermore, although not significant, we found that the use of supplements before and in early pregnancy was associated with lower odds of more severe CL/P. This follow previous studies showing that an association between NSOFC and maternal nutritional deficiencies during early pregnancy [41] Vitamin B and folic acid supplementation were previously reported to be associated with lower risk of NSOFC in infants [42]. Also, an animal study on mice with CP mutation (Tgf-B3-/-) found that folic acid supplementation significantly minimized CP severity by improving palatal shelf adhesion and disposition of collagen IV, cytokeratin-17, laminin, and fibronectin [43].
Finally, we found higher odds of CL/P severity with maternal nicotine use. However, this association was not statistically significant due to the small number of mothers reporting smoking. This could have resulted from the social stigma against women using nicotine [44]. Furthermore, the lifestyle behavior changes during COVID-19 lockdown might have affected smoking prevalence and in some way affected the previously known association between smoking and CL/P [45].
There are a few limitations in this study. First, the history of COVID-19 infection might have been prone to some recall bias although this would be minimal considering the emphasis on COVID-19 infection status during the pandemic and that data collection occurred in the same week of delivery. Second, misclassification bias may be another limitation in the study since not all infected cases were tested, with chances for over or under estimation of the observed relation. Third, the generalizability scope of the findings is limited to the 5 countries included in the study and extrapolation to other countries needs to be carefully considered in view of the variation in the distribution of the exposures and determinants by country. Furthermore, the sample size, although exceeding the suggested sample size calculation, is recommended to be enlarged. However, in this study, the availability of cases was limited because it was conducted on a congenital anomaly; which is a rare condition (with 1.17/1000 prevalence) and was limited to the COVID-19 period [46]. Nevertheless, the study has several important findings.