Does gestational diabetes mellitus affect the hearing of the baby?

INTRODUCTION

Gestational diabetes mellitus (GDM) is defined as carbohydrate intolerance of variable severity with onset or first recognition during the present pregnancy.¹ Theoretically speaking, diabetes mellitus is a condition of insulin resistance with impairment of microcirculation with complications such as microangiopathy and neuropathy. Although such complications are more common in long standing cases of diabetes mellitus, ladies with pregestational poor glycaemic control may be diagnosed only during pregnancy and might be labelled as gestational diabetes mellitus. Since the inner ear is sensitive to ischemia, it is possible that diabetes mellitus in the mother can affect the hearing in the new-born.² Infants of diabetic mothers have been found to have higher malformation rates like caudal regression, situs inversus, duplex ureters, renal agenesis, cardiac anomalies, etc. ³Gestational diabetes mellitus is a known risk factor for complications like polyhydromnios, hypoglycemia in the baby, seizures, electrolyte imbalance, NICU admission.¹ Its role in affecting hearing in the baby is yet to be established. Otoacoustic emissions result from the energy generated in the cochlea that are propagated through the middle ear and into the ear canal where they can be measured using a sensitive microphone.⁴ Hence, it can be used as an effective screening tool to assess the effect of gestational diabetes mellitus on the hearing of the new-born.

Objectives

An objective of current investigation was to study the effect of gestational diabetes mellitus on the hearing of the new-born.

METHODS

The study was carried out between December 2018 and May 2020. It was a prospective institution-based study. All the babies born in the study period in the study institution Mcgann teaching district hospital, Shivamogga were screened for hearing loss. Out of these babies, only the babies born to mothers with gestational diabetes mellitus were taken as the sample size for this study. A total of 14226 babies were screened, of which 44 babies were born to mothers with gestational diabetes mellitus.

Inclusion criteria

All the babies born in the hospital during the study period were included in the study.

Exclusion criteria

Exclusion criteria for given study were; babies requiring urgent referral to higher centres, discharge against medical advice and death of baby before discharge from hospital.

Procedure

The babies left to be by the mother’s side and were screened in the postnatal ward and babies referred to neonatal intensive care unit (NICU) were screened in the NICU. A soft probe tip of size enough to achieve seal was inserted into the external auditory canal of the baby and DPOAE (distortion product otoacoustic emission) was recorded for both ears separately. No further testing was done for babies with a “pass” result. The babies who failed the first screening were recalled for repeat OAE after one month and if they failed the test again, they were asked to come again after a month. In case of a “refer” result on the third time, such babies were referred for BERA. The details of all the babies were entered in Microsoft excel software and follow ups were updated accordingly. Details of the babies born to mothers with gestational diabetes mellitus were later collected from the previously entered data. To test the effect of gestational diabetes mellitus on the hearing of the new born, test of significance- Chi-square test was applied after creating a 2x2 table.

RESULTS

A total of 44 babies born to mothers with gestational diabetes mellitus were screened within 24-48 hours of birth. 6 babies had a “refer” result and were requested to come for a second OAE testing.

In the second OAE, out of the 6 babies screened, only 1 baby failed the test and the rest 5 babies passed the test.

Even this baby passed the OAE testing when tested for the third time. There were no babies born to mothers with gestational diabetes mellitus who required BERA testing.

On applying the Chi-square test, the result is insignificant with p value 0.181.

Chi-square test was applied to the statistical data and there was no significant difference observed between the outcomes in both groups.

DISCUSSION

A total of 44 babies born to mothers with gestational diabetes mellitus were screened within 24-48 hours of birth. 6 babies had a “refer” result and were requested to come for a second OAE testing. In the second OAE, out of the 6 babies screened, only 1 baby failed the test and the rest 5 babies passed the test. Even this baby passed the OAE testing when tested for the third time. There were no babies born to mothers with gestational diabetes mellitus who required BERA testing. A prospective study was done by Kountakis et al to identify potential risk factors for neonatal hearing loss. They concluded maternal diabetes as one of the potential risk factors for hearing impairment in the baby.⁵ In a study by Jun-Hong Zhou et al, a significant difference was seen in the result of hearing screening between babies born to GDM and non GDM mothers. 69 GDM mothers were considered in the study and 597 non GDM mothers were considered. 7 babies of non GDM mothers and 3 babies of GDM mothers failed the screening. The chi square test showed a p value of <0.05. It was concluded that GDM increases the incidence of abnormal hearing in newborns.⁶ In a study by Angeli C. Carlos-Hiceta et al it was found that the odds of having a ‘refer’ result in the initial hearing screening test (transient evoked otoacoustic emissions) of a baby born to a diabetic mother is 2x higher when compared with the results of a baby born to a non-diabetic mother.⁷ But unlike our study, this study considered both gestational and pregestational diabetes mellitus. A retrospective study was conducted by Fatih Mehmet Hanege et al, comparing the otoacoustic emissions between infants born to healthy women and women with GDM. In the study, the study group consisted of 79 infants born to mothers with GDM and control group had 100 infants born to healthy mothers. There was no difference between the hearing screening results of the two groups.⁸ In our study, similar to the above study, no significant difference in the results of two groups were observed (Figure 1). Hence, gestational diabetes mellitus could not be mentioned as an independent risk factor for hearing loss in the baby.

Limitations

A limitation of the current study was that study required multiple visits to the hospital.

CONCLUSION

Although diabetic microangiopathy is a possible risk factor for cochlear ischemia in the foetus and subsequent hearing loss, in practice it is less common because diabetic microangiopathy is a late complication of diabetes mellitus and gestational diabetes has a comparatively shorter history. Gestational diabetes can also predispose the mother for development of pre-eclampsia, which is another risk factor for hearing impairment in the baby.¹This study aimed at assessing gestational diabetes as an independent risk factor for hearing loss in the baby and it was concluded that gestational diabetes does not affect the hearing in the baby. More studies need to be undertaken to authoritatively establish or dismiss the role of gestational diabetes in the hearing impairment of the new born.

ACKNOWLEDGEMENTS

The authors acknowledge the department of obstetrics and gynecology and department of paediatrics for allowing the screening to be conducted in their wards and NICU respectively.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee

REFERENCES

1. 1. Konar K. Medical and surgical illnesses complicating pregnancy. In: DC Dutta’s textbook of Obstetrics. 9^th ed. New Delhi: Jaypee Brothers Medical Publishers Ltd; 2018:262-6.
2. 2. Tabuchi K, Nishimura B, Tanaka S, Hayashi K, Hirose Y, Hara A. Ischemia-reperfusion injury of the cochlea: pharmacological strategies for cochlear protection and implications of glutamate and reactive oxygen species. Curr Neuropharmacol. 2018;8(2): 128-34.
3. 3. Mills JL. Malformations in infants of diabetic mothers. Birth Defects Res A Clin Mol Teratol. 2010; 88(10):769-78
4. 4. Prieve B, Fitzgerald T. Otoacoustic Emissions. In: Chasin M, English K, Hood LJ, Tillery KL, eds. Jack Katz-Handbook of clinical audiology. 7th ed. Philadelphia: Walters Kluwer; 2015:357-79.
5. 5. Kountakis SE, Skoulas I, Philips D, Chang CYJ. Risk factors for hearing loss in neonates: A prospective study. Am J Otolaryngol. 2002;23(3):133-7.
6. 6. Jun-Hong Zhou, Kang Yu, Hui Ding. A clinical study on gestational diabetes mellitus and the hearing of newborns. Diabetes, Metabolic syndrome and Obesity: Targets and Therapy. 2021;14:2879-82.
7. 7. Carlos-Hiceta AC, Rina MT. Maternal Diabetes: A Potential Risk Factor of Congenital Hearing Loss. Acta Medica Phillipina. 2021;55(1):75-9.
8. 8. Hanege F, Yilmaz HB, Celik S, Gocmen A, Kalcioglu M. Is gestational diabetes a risk factor for neonatal hearing loss?. Arch Clin Experiment Med. 2019:45: 29-32.