Interpretation
The rates of pre-labor and laboring cesarean in our data are very
similar to those in a 2016 hospital birth population in Sydney,
Australia6. However, comparable studies on the
contribution of primary cesarean without attempting vaginal birth to the
total cesarean birth rate in the US are limited and are based on births
that pre-date the 2014 ACOG guidance aimed at reducing cesarean
birth.2
Our observation thatprimary pre-labor cesareans in singleton term cephalic
pregnancies, constitute 6.6% of all cesareans births, is similar to the
7.9% rate reported by Zhang et al.9 using chart
abstracted data on births between 2002 and 2008 from the Consortium on
Safe Labor cohort. Joesch et al.10, using
administrative (procedural code) data, reported that between 1979 and
2004 the rate of primary pre-labor cesarean as a proportion ofall live births varied between 4.5% and 6.6% which is similar
to the 6.7% observed in our study.
Huesch et al.11, reported variation in pre-labor
cesarean rates among hospitals in their study and highlighted the
pre-labor cesarean rate as a potentially important metric. However, the
heavy reliance on administrative data for quality improvement in
maternity care in the US is a barrier to using pre-labor cesarean as a
metric. Pre-labor and laboring cesarean are not easily distinguishable
in administrative data and rely on the assumption that if there is an
ICD procedural code for cesarean in the absence of a code consistent
with labor, pre-labor cesarean was the mode of delivery. This involves
searching for multiple procedural codes and may be subject to
reliability issues.
National birth certificates provide another data source for evaluating
cesarean birth in the US. However, the finding by Hehir et
al3 that pre-labor cesareans in Robson groups 2b and
4b (singleton term cephalic pregnancies with no history of cesarean),
constitute 27% of all cesarean births when using US Birth Certificate
data compared to 6.6% in our data raises the possibility of
misclassification in the US national birth certificate data.
On examining indications for cesarean in Robson groups 2b and 4b in our
clinical dataset, the rate of pre-labor cesarean without a medical
indication in the nulliparous term cephalic singleton population was low
0.6%, suggesting that cesarean for maternal request is uncommon in
first time mothers. This is consistent with other
authors.12 The finding that suspected macrosomia was
the most common indication for primary cesarean without attempting
vaginal birth in singleton term cephalic pregnancies was unexpected and
may be an increasingly common indication.13 A study
from France reporting on potentially avoidable planned cesarean births
also reported suspected macrosomia to be one of the more common stated
indications.14 ACOG does not consider suspected
macrosomia to be an indication for cesarean birth unless the estimated
fetal weight is >4500g in a diabetic woman or
>5000g in a non-diabetic woman, when “prophylactic
cesarean delivery may be considered”.15 It is
therefore of concern that we found birth weight was <4500g in
more than 3/4 of cesareans performed without attempting vaginal birth
for suspected macrosomia in singleton term cephalic nulliparous
pregnancies. Our findings are consistent those of Boyle et
al.16 who reported 80.3% of primary cesareans
performed for fetal macrosomia were associated with an actual birth
weight of <4500g.
The basis for “suspected macrosomia” could not be determined from the
OB COAP database but it seems likely that ultrasound-derived estimated
fetal weights contributed in many cases. A “large for dates” diagnosis
based on ultrasound measurements has been associated with an increased
risk for both pre-labor and intrapartum cesarean independent of the
actual birth weight of the baby.17,18