Interpretation
Advanced maternal age resulted as an independent RF for caesarean
section in Robson groups 1, 2A, 3, and 4A. We have recently
shown11 that maternal age ≥40 years represents a RF on
CS rate strongest than parity.
The presence of diabetes significantly increased the risk of CS delivery
in groups 1 and 5 but its effect was not significant in the other
groups. Our data are in contrast with the results of Zeki et
al14 that showed that diabetes increases the CS rate
in all groups except Group 1. These differences may be due to the
different CS rate in the study populations (i.e. lower in our study).
Despite the uncertainty of these evidences, diabetes has to be taken
into consideration when comparing CS rates, since it is likely to play a
role regardless of the Robson group.
Hypertensive disease was identified as a RF in groups 2A (OR 1.32) and 5
(OR 3.49), probably because the decision to perform a CS in labour is
taken earlier if a nulliparous undergoes induction of labour for
hypertension or she has a previous uterine scar. Also, hypertension
represented the strongest RF for CS in group 10 (OR 3.7) probably
because in this group the disease is more severe thus to anticipate the
time of delivery is a common prudential clinical behaviour. In
multiparous without a uterine scar, hypertension did not reach
statistical significance. The association between severity of
hypertension and CS has been previously shown6.
However, in our study, similarly to what Gerli et
al.15 showed in Robson’s classes 1 and 3, hypertension
represents a RF for caesarean section in nulliparous but not in
multiparous. Obesity increased the CS rates in nulliparous women at term
(i.e. groups 1 and 2A) but not in multiparous at term (i.e. groups 3 and
4A). Also, in this case our results are similar to those of Gerli et
al.15 in a population similar to ours. However,
unexpectedly, in our population, obesity decreased the risk of CS in
group 5 women attempting TOLAC. It is well known that increasing BMI has
an inverse association with the likelihood of achieving vaginal
birth16. A possible explanation could be that, given
that caesarean sections in labour and in obese women, involves greater
difficulties and complications, the decision is postponed, in an attempt
to avoid surgery, with a consequent greater probability of obtaining a
vaginal birth16; alternatively, it could be that only
obese women who are more likely to be successful in vaginal delivery are
admitted to TOL. Nulliparous women at term (group 1 and 2A) and
multiparous women in spontaneous labour (group 3) with macrosomic
fetuses were more likely to have a CS. Of note, macrosomia was one of
the two RFs that more than doubled the risk of CS in group 3. The
association between macrosomia and CS is well-known9and a recent trial10 proved that, when macrosomia is
suspected, labour induction at an earlier gestational age increases the
likelihood of vaginal delivery.
Obstetrics analgesia and ethnicity behaved as risk or protective factors
depending on the Robson group. According to our data, obstetric
analgesia increased the risk of CS in nulliparous women in spontaneous
labour, while decreased the risk when labour was induced. In addition,
it decreased the risk of CS in groups 5 and 10. A recent
meta-analysis13 concluded that epidural analgesia has
no impact on the risk of caesarean section. As a matter of fact, in our
analysis we included every type of pharmacological pain control (i.e.
intravenous drugs, epidural analgesia), so that it is difficult to make
any comparison. Probably, more studies are necessary to define the role
of obstetric analgesia as a risk or protective factor for CS rates in
the different Robson groups.
Being immigrant, in our study, was a protective factor in groups 1 and
10 and a RF in group 4A. A metanalysis by Merry et
al.17 that evaluated CS rates between immigrants and
non-immigrants women revealed higher CS rate for Sub-Saharan African,
Somali and South Asian women; higher emergency rates for North
African/West Asian and Latin American women; and lower rates for Eastern
European and Vietnamese women. However, they did not evaluated
differences between Robson groups. A study by Minsart et
al12 demonstrated an increased risk in group 1, 2, 3
and 4 for mothers from Sub-Saharan Africa compared with Belgian natives,
while a reduced risk for East European women in group 1. A recent study
by Linard et al18 demonstrated a higher CS rate for
Sub-Saharan African women in group 5 with only one previous uterine
scar, compared to French women. Anyway, it is not possible to compare
these studies because the ethnic groups taken into consideration are
different and data are heterogeneous.
The statistically significant reduction of CS rate in Robson groups 2A,
5, and 10 reflects the efforts made by our institution to avoid
unnecessary CS. It is likely that the weekly audit system adopted in our
institution, together with the use of standardized and updated protocols
and the publication of annual reports, has played, and can continue to
play, a decisive role in reducing CS rates. The implementation of the
“trial of labour after caesarean section” helped to reduce the number
of CS in Robson group 5, while the reduction in group 2A it is probably
due to the fact that our labour induction protocol allows wait a longer
period of time to declare the procedure failed19. On
the other hand, we think that our CS rate in multiparous women (Robson
groups 3 and 4A) and in nulliparous women in spontaneous labour was
already adequate, according to international
standards2, so that a further reduction could be
harmful.