Results and Clinical implications
We present the obstetrical outcomes of vaginal delivery after Cesarean
delivery in women with and without large estimated fetal weight. Only
70.5% of women in the study group compared to 80.5% of controls
experienced successful vaginal delivery (p = 0.03). This finding is in
agreement with other series that examined the TOLAC’s success rate,
which showed that vaginal delivery can be achieved in 60-80% of women
(8, 9). However, unlike our study, those studies did not separate eLGA
and non eLGA fetuses and therefore the rate of successful TOLAC in cases
of eLGA fetuses cannot be elaborated.
There are several possible explanations to the difference in success
rate between the two groups. One can reasonably assume, that the larger
the fetus the lower the chances for successful TOLAC and the current
cutoff of 4000g does not suffice. Peaceman et al. (11) reviewed the
pregnancy outcomes of women whose first CD was performed because of
dystocia, and found that for each 100 gram increase in birthweight
relative to the first pregnancy there was 3.8% decrease in the odds of
successful TOLAC. Yet, while macrosomia is considered a relative
contra-indication for TOLAC, eLGA alone is not.
Women in the study group were significantly older (35 vs. 33 years;
p=0.004) and, as expected, with higher gravidity (4 vs. 3; p=0.001).
Nevertheless, higher gravidity is also associated with higher
birthweight (12), and hence, lower rates of TOLAC. As we excluded all
women who underwent more than one CD, women in the study group had more
previous vaginal deliveries which should have increased their chances
for a successful TOLAC (7). However, as mentioned before, we found a
lower rate of successful VBAC amongst women in the study group. One
reasonable explanation is that eLGA may have a greater effect on the
likelihood of a successful TOLAC.
Women in the study group had higher BMI compared to the controls (30.9
vs.27.5 kg/m²; p=0.001). This finding is in accordance with the findings
of Shin et al. (13) who reported that high BMI is an independent risk
factor for LGA infants (13). For women attempting TOLAC, both LGA
fetuses and high BMI lower the chances of TOLAC success (11, 14). It
should be noted that there was no significant difference in GCT nor in
gestational diabetes (GDM) between the study group and controls (p=0.97
and p=0.68 respectively). Therefore, we deduced that GCT and GDM can be
ruled out as confounders to our primary outcome.
The rate of PPH was significantly increased in the study group compared
to controls (7.7 vs.1.7%; p=0.001). A possible explanation for the
increased rate of PPH among women in the study group could be attributed
to the effect of the LGA fetus on the uterus which may cause atony. This
explanation correlates with a previous study where pregnancies with LGA
infants were found at higher risk for PPH (15).