Page 53 - JCTR-11-4

Journal of Clinical and
Translational Research Female are better in otoacoustic emissions tests

deliveries is higher in the twin group compared to the believed. Being a monozygotic twin is not the same as being
general population, and their discharge day is later (>72 h) dizygotic, as demonstrated by McFadden and Loehlin
34
compared to vaginal births (48 h). It has been demonstrated when evaluating the genetic influence on spontaneous
that the maximum intensity of OAEs is reached starting OAEs in identical and fraternal twins. They found greater
from days 3 to 4. 31,32 In addition, twins received a lower concordance in the auditory responses of monozygotic
proportion of breastfeeding, which is another positive twins compared to dizygotic twins, although sex differences
factor for OAEs. 29,33 remained significant in both types. They concluded that
This makes it particularly interesting to analyze pairs both genetics and the intrauterine environment influence
of different-sex twins with discordant OAE results since spontaneous OAEs, with sex differences suggesting
they are discharged on the same day. In this subgroup, the a complex interaction of factors. The similarity in
differences are significant, favoring females, although the spontaneous OAEs among monozygotic twins indicates a
groups are small. This confirms the superior response of strong genetic influence on auditory development. There
females under equal conditions. may be specific genes that affect auditory function and are
expressed differently depending on sex.
Several studies on twins also demonstrate a positive
effect of the female gender. Studies evaluating premature Another factor to consider could be nutritional
twins for auditory differences by sex found that females competition, as the availability of nutrients and hormones
had higher OAE amplitudes than males, even during may vary in twins, differentially affecting auditory
early developmental stages. These differences persisted development.
regardless of factors such as birth weight or gestational age. 4.4. Study limitations
Furthermore, Johansson et al. reported that, in both The EchoCheck screener does not output absolute TEOAE
7
samesex and differentsex twin pairs, TEOAE amplitudes amplitudes. The test without normal results merely
were appreciably greater in right ears and females than indicates whether the response corresponds to a hearing
in left ears and males - a pattern previously observed in loss greater than 30 dB hearing loss. Future work should
young adult twins and large cohorts of neonates. employ instruments that provide amplitude data so that the
However, the relationship in twin pregnancies may magnitude of any intergroup differences can be quantified.
be more complex due to the influence of the co-twin’s The present investigation used the nonlinear protocol
sex. Specifically, females with male twins may have less that dominates routine TEOAE recording. This
8,32
intense OAEs than females with female twins, likely due sequence delivers three clicks of identical polarity followed
to exposure to male hormones in utero. This was described by a single click of the opposite polarity at triple intensity,
by McFadden and Loehlin, who studied monozygotic enabling cochlear activity to be detected despite linear
34
(identical) and dizygotic (fraternal) twins to evaluate the artifacts. Nevertheless, because all linear components of
heritability of spontaneous OAEs. They found that females the waveform are subtracted, a portion of the genuine
had stronger emissions than males. In addition, female OAE signal is inevitably discarded, yielding a generally
twins showed greater similarity in OAEs than male or modest signaltonoise ratio. Including a linear recording
mixed-sex twins. They concluded that heritability plays condition alongside the nonlinear protocol may therefore
a significant role in OAEs, and sex differences suggest a be advisable in subsequent studies.
prenatal hormonal influence.
Finally, the EchoCheck device analyzes emissions only
Moreover, within the context of twin studies,
McFadden also investigated women who had a male within 0 – 4 kHz. Work employing equipment that extends
35
to higher frequencies is required to establish whether
twin and found that these women had less intense OAEs clinically relevant sex- or earrelated effects arise outside
than women with a female twin. It was suggested that this band.
prenatal exposure to testosterone from a male twin could
masculinize the female auditory system. The presence Given that healthy newborns were examined for
of a male twin may influence the auditory development this study, it remains unknown if gender increases the
of the female twin through shared hormonal exposure susceptibility to other neonatal hearing loss factors. In
in utero. This hormonal exposure may lead to partial addition, perhaps other unknown perinatal factors can
masculinization of the auditory system, resulting in lower vary the response in newborns. More studies in this area
amplitude OAEs in girls with male twins. are needed.
Moreover, the relationship between monozygotic and In this study, no distinction was made between
dizygotic twins may be more complex than is commonly monozygotic and dizygotic twins, which could also be of

Volume 11 Issue 4 (2025) 47 doi: 10.36922/jctr.8416