You’d be forgiven for thinking that it meant, “Women with hearing loss [are] more likely to have preterm or low birth weight babies [than those without hearing loss.]”
But what’s the actual story?
The American Journal of Preventive Medicine recently published the findings of a study entitled “Birth Outcomes Among US Women with Hearing Loss.” The study compared the ‘birth outcomes’ of babies born to normal hearing mothers with those of babies born to mothers with hearing loss, and claimed that babies born to women with hearing loss were significantly more likely to be premature and have low birth weight, than babies born to hearing mothers.
On seeing this headline, I thought, “What? Hearing loss causes premature birth? How can that be?” It seemed to defy logic and so I delved a little deeper, reading not just the media summaries but the actual scientific study itself.
The aims of the research seemed admirable enough:
“The purpose of this study is to estimate the national occurrence of deliveries in women with hearing loss and to compare their birth outcomes to women without hearing loss.”
Lead investigator Monika Mitra, PhD, of the Lurie Institute for Disability Policy, Brandeis University, in Waltham, MA was quoted as saying:
“There have not yet been any population-based studies about pregnancy experiences and outcomes among women with hearing loss, although a recent study of deaf women’s experiences with prenatal care found they were less satisfied with their care and were more likely to have fewer prenatal visits than hearing women. We therefore set out to investigate birth outcomes among women with hearing loss,”
This all sounds like a positive motive so perhaps it was just ‘sloppy journalism’ that led to the headline.
I delved deeper…
The researchers examined the figures of the Nationwide Inpatient Sample of the Healthcare Cost and Utilization Project (HCUP) 2008–2011 to compare birth outcomes in women with and without hearing loss, including ‘preterm birth’ and ‘low birth weight’. Approximately 10,500 of the 18 million or so deliveries were by ‘women with hearing loss’. (We’ll come onto how they ascertained the women had hearing loss shortly so, please bear with me.) The researchers said that there was a statistically significant difference in the rate of babies born preterm and/or with a low birth weight, such that it was statistically more likely in those who reported they had hearing loss.
However, as my statistics professor at university used to say, “Correlation does not suggest causality,” and there was nothing in the finding that suggested ‘having hearing loss per se was linked to premature birth or underweight babies.
“Women with hearing loss are more likely to be publicly insured and can qualify for both Medicare and Social Security Disability Insurance on the basis of their hearing disability, especially if their disability prevents successful employment. Medicare and Medicaid were the most common payers for delivery hospitalizations among women with hearing loss, but private insurance was most common among women without hearing loss. Nearly one in seven women with hearing loss had their births paid for by Medicare, which was significantly higher than Medicare coverage for women without hearing loss (13.3% versus 0.6%). Women with hearing loss were almost two times more likely to have one or more coexisting health issues and were also more likely to be admitted to urban teaching hospitals.”
So, perhaps the ‘coexisting health problems’, poverty, type of medical care and/or type of hospital they were admitted to were as much to contribute to the birth outcomes of babies born to mothers with hearing loss?
And, bearing in mind this research relied on combing through statistics gathered between 2008 and 2011, how did the researchers determine whether or not the mothers had hearing loss? And did they look at the type and severity of the hearing loss?
In terms of the severity of hearing loss, I could find no reference to that in the study: for the ‘classification of hearing loss’, the study used this:
Classification of Hearing Loss
Conductive hearing lossa
Sensorineural hearing lossb
Mixed conductive and sensorineural hearing loss
Deaf nonspeaking, not elsewhere classifiable
Other specified forms of hearing loss
Unspecified hearing loss
aExcludes: mixed conductive and sensorineural hearing loss (389.20–389.22).
bExcludes: abnormal auditory perception (388.40–388.44).
The discursive part of the paper says:
“The estimates are conservatively biased because some women with HL [hearing loss] were probably not assigned the ICD-9 code for their HL. Therefore, the weighted estimate of 10,462 deliveries for the 2008–2011 period occurring to women with HL should not be interpreted as an incidence statistic. Yet, the smaller-than-anticipated number may be reflective of not-well-understood providers’ coding behaviors. For example, healthcare providers may only be prompted to add ICD-9 HL codes when the HL resulted in significant communication barriers during the hospital visit. Undercoding and underdiagnosis of HL is a common issue across different types of healthcare visits.”
So, there were an undisclosed number of mothers who had hearing loss who had babies that were not preterm or underweight, but they could not be identified in the sampling used because of a weakness in the way the original data was collected?
The study went on to say, “Patients may be reluctant to disclose their hearing loss owing to fear of discrimination, perceptions of disability, and vanity.”
I would hazard a guess that they were possibly also too busy giving birth to bother mentioning their hearing loss! How many of us just ‘get on with things’ on a day-to-basis without bothering to mention our hearing loss to strangers, even if they are healthcare providers?
The study acknowledges further ‘limitations’ including the lack of data on marital status, a weakness in how ‘household income’ was estimated, and the exclusion of birth outcomes of home-births during this period. Despite this, the lead investigator is quoted as saying:
“Given the earlier studies on patient–provider communication, potential biological factors, interpersonal violence, and health knowledge and health literacy among people with hearing loss, and the general dissatisfaction of people with hearing loss with their healthcare, these factors could potentially explain the poor birth outcomes found in this study.”
Whilst I accept the claim the researchers’ assertions that ‘healthcare providers rarely receive training on how to communicate effectively and care for individuals with hearing loss, resulting in poor communication,’ I fail to see how that would account for a statistical significance in preterm births or underweight babies.
What do you think?