Certain
clinical
and
demographic
factors
were
associated
with
higher
rates
of
obstetric
anal
sphincter
injury
(OASI)
among
first-time
mothers
during
vaginal
birth,
a
large
cohort
study
found.

In
a
study
of
more
than
half
a
million
previously
nulliparous
women
giving
birth
in
California,
OASI
occurred
in
4.4%
with
operative
delivery
being
the
strongest
risk
factor,
reported
Christina
Chambers,
PhD,
of
the
University
of
California
San
Diego,
and
colleagues.

OASI
occurred
in
20%
of
forceps-assisted
deliveries
(adjusted
relative
risk
[aRR]
4.38,
95%
CI
4.11-4.68)
and
12.3%
of
vacuum-assisted
deliveries
(aRR
2.95,
95%
CI
2.86-3.04),
compared
to
just
3.5%
of
nonoperative
vaginal
deliveries,
they
wrote
in


JAMA
Network
Open.

Demographics
also
affected
the
OASI
risk
estimates.
Compared
to
non-Hispanic
white
women,
those
of
Asian
ancestry
showed
nearly
doubled
risk
(aRR
1.92,
95%
CI
1.86-1.99)
while
Black
and
Hispanic
women
both
had
lower
risk
of
OASI.

Also,
women
with
maternal
diabetes,
preeclampsia,
and
delivery
of
a
large-for-gestational-age
infant
were
at
heightened
risk,
while
those
with
obesity
prior
to
pregnancy
had
lower
risk.

Co-author
Lindsey
Burnett,
PhD,
MD,
also
of
the
University
of
California
San
Diego,
told

MedPage
Today
that,
as
a
urogynecologist,
she
sees
a
lot
of
women
with
OASI
and
its
sequelae.

“The
number
one
question
that
I
get
from
patients
is,
‘Why
did
no
one
tell
me
this
could
happen
to
me,
and
what
was
my
risk
of
getting
it?'”
Burnett
said.

Approximately
216,000
U.S.
women
experience
OASI
annually.
Severe
perineal
injuries
like
OASI
often
result
in
long-term
pelvic
floor
disorders
—
such
as
pelvic
organ
prolapse,
stress
urinary
incontinence,
and
overactive
bladder
—
and
about
three
in
10
women
report
impaired
quality
of
life
from
anal
incontinence
afterwards,
the
paper
noted.
Cesarean
delivery
on
maternal
request
is
the
only
known
intervention
that
completely
eliminates
OASI
risk.

“The
inspiration
for
this
research
approach
was
to
think
about
what
we
can
do
to
better
guess
who
would
benefit
from
preventive
intervention,
and
to
personalize
the
discussions
about
the
risks
of
having
these
types
of
tears
that
put
people
at
risk
of
having
really
severe
pelvic
floor
disorders
later,”
Burnett
explained.

“When
we’re
trying
to
design
better
ways
to
engage
patients
in
personalized
care,
we
really
need
to
be
tailoring
counseling
towards
their
specific
risk
rather
than
overall
risk,”
she
continued.

It
was
already
known
that
operative
delivery
was
a
risk
factor
for
OASI,
which
makes
sense
considering
forceps
and
vacuums
can
“come
into
the
sphincter
complex
and
really
compromise
the
ability
for
it
to
function
later,”
Burnett
said.

To
better
describe
the
risk
factors
associated
with
OASI,
the
research
team
conducted
a
population-based
analysis.
They
looked
at
all
nulliparous
women
with
singleton,
full-term
pregnancies
(37
to
44
weeks’
gestation)
who
delivered
live-born
infants
in
California
between
2016
and
2021,
linking
birth
certificates
to
hospital
discharge
records.

From
the
birth
certificate
data,
authors
collected
maternal
information,
including
age
at
delivery,
self-reported
race
and
ethnicity,
education,
expected
payer
for
delivery,
and
type
of
birth
attendant,
as
well
as
neonatal
factors
including
gestational
age
at
delivery
and
birth
weight.
Maternal
diabetes
and
hypertensive
disorders
were
determined
from
birth
certificates
and
maternal
discharge
records.

A
total
of
577,510
nulliparous
women
met
the
eligibility
criteria,
of
whom
85%
were
age
18-34.
In
this
cohort,
42%
of
patients
were
Hispanic,
30%
non-Hispanic
white,
18%
Asian,
and
4%
were
Black,
with
the
rest
classified
as
“other”
or
unknown.

OASI
was
identified
via
ICD-10
codes
for
third-
and
fourth-degree
perineal
lacerations.
The
reference
group
were
those
with
no
or
first-degree
lacerations,
who
were
compared
against
those
with
second-degree
lacerations
and
those
with
OASI.

“This
large
population-based
cohort
study
confirmed
established
risk
factors
for
OASI
and
identified
several
nonmodifiable
risk
factors,”
the
investigators
wrote.

Chambers
and
colleagues
noted
some
limitations,
including
the
retrospective
study
design,
the
probable
underreporting
of
OASI
in
administrative
data,
and
potential
confounding
by
indication
for
birth
attendant
type.
The
available
data
also
lacked
information
on
episiotomy
use,
fetal
head
position,
second-stage
labor
duration,
clinician
experience,
or
perineal
protective
maneuvers
that
could
influence
OASI
risk.

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