Journal Club: Systematic review on pregnancy and inner ear disorders

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Today's journal article

Timms S, Stapleton E. Effects of pregnancy and pregnancy-related conditions on the inner ear: a systematic review. 

Why I picked this article

Pregnancy changes nearly every system in the body. During pregnancy, women go through persistently high circulating levels of oestrogen and progesterone hormones, affecting various aspects of the body. 

Patients often report blocked-ear sensations, tinnitus, dizziness, or sound sensitivity, and clinicians wonder what is truly pregnancy-related versus coincidental. Hormonal changes and increased blood volume could, in theory, impact our inner ear function. 

This systematic review pulls together the literature on pregnancy and inner ear diseases such as hearing loss and vertigo. Researchers then looked into about what we actually know about hearing and balance during pregnancy and in pregnancy-related conditions such as pre-eclampsia and gestational diabetes.

Some of the research findings

Systematic review method: 
  • Pre-registered systematic review (PROSPERO CRD42023446898), PRISMA 2020 compliant. 
  • Two authors independently searched databases: PubMed, Embase, CINAHL and the Cochrane Library.
  • Search terms:  (pregnan* OR gestational diabetes OR pre-eclampsia OR preeclampsia) AND (auditory OR hearing OR vestibular OR tinnitus OR misophonia OR phonophobia OR hyperacusis OR decreased sound tolerance)
  • Databases search conducted: Aug 2, 2023, to Jan 23, 2025. 
  • Sixty-nine studies met the inclusion criteria for qualitative synthesis. Those included: 
    • 29 prospective observational research studies
    • 8 retrospective review studies
    • No interventional randomised controlled trials. 
    • 9 case series
    • 14 individual case studies
    • 7 reviews
Normal pregnancy
  • Hearing: 
    • Subclinical, reversible low-frequency hearing threshold shifts (~3–5 dB on average) were observed during pregnancy and improved after childbirth. 
    • Distortion-product otoacoustic emissions were absent more often in pregnant vs non-pregnant adults (26% vs 4%) despite normal pure-tone thresholds. Tinnitus and aural fullness were reported more frequently in pregnancy.
    • Sudden sensorineural hearing loss does not appear more frequent in pregnancy; literature focuses on safe management when it occurs.
  • Vestibular symptoms and hyperemesis
    • Evidence suggests vestibular function can shift during pregnancy.
Pregnancy-related conditions
  • Pre-eclampsia: 
    • Multiple studies showed worse hearing thresholds at several frequencies vs healthy pregnant controls. 
    • One study found changes persisted post-partum, consistent with microangiopathy/endothelial dysfunction affecting the inner ear.
  • Gestational diabetes: 
    • Higher-frequency (8–14 kHz) thresholds were worse and did not recover at 4 weeks post-partum
    • ABR peaks I–V had prolonged latencies and reduced wave V amplitude, indicating slowed neural conduction/central involvement.
Limitations identified in the study are that the evidence base is largely observational (no randomised trials); heterogeneity and publication bias are likely. 

(Image from Pixabay.com, TerriC)

Haruna's takeaway

The main takeaway personally was that, like in many cases for humans, we don't seem to know much about how the inner ear is affected in humans by various factors; in this case, the pregnancy. This is due to the lack of diagnostic tools that enable us to assess the state of the inner ear in humans. Given that the hormones affect fluid balance, and the inner ear is a super delicate, fluid-filled labyrinth, it would be surprising if the inner ear is not affected by an increased risk of hearing loss or vestibular dysfunction. I also wonder what the long-term impact of pregnancy is. The pregnancy and hormonal changes affect bone metabolism, and our inner ear and middle ear are very much dependent on healthy bony structures. 

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This is Haruna's 81/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.