TIMING OF DELIVERY
There is an increased risk of stillbirth in gestational
diabetic pregnancies, particularly when glucose concentrations
are not within target ranges and the fetus
is presumably hyperinsulinemic. A 2011 workshop
jointly sponsored by the Eunice Kennedy Shriver National
Institute of Child Health and Human Development
and the Society for Maternal-Fetal Medicine recommended
that gestational diabetic pregnancies in
which glucose concentrations are well controlled, with
or without medication, not be delivered electively before
39 weeks (59 ). When GDM is poorly controlled
the timing of delivery is individualized and is generally
between 34 and 39 weeks, depending upon the situation.
When all of almost 200 000 pregnancies complicated
by GDM in California over a 10-year period were
analyzed, the stillbirth rate plus infant mortality rate
associated with delivery at various gestational ages was
compared to determine the risk of early delivery vs
waiting 1 more week (60 ). Such risks were not different
between 36 and 38 weeks, but at 39 weeks and beyond
the relative risk of expectant management exceeded
that of delivery. The absolute differences were small but
significant, with the number needed to deliver at 39
weeks (vs 40 weeks) to prevent a single excess death
being 1518. Because there is increased perinatal morbidity
associated with early term delivery before 39
weeks (61 ), delivery between 39 and 40 weeks in cases
of gestational diabetic pregnancy appears to be a reasonable
course. At our institution we recommend induction
of labor for undelivered women with wellcontrolled
gestational diabetes at some time between
39 and 40 completed weeks of gestation, depending
upon the patient’s preference. Delivery is often performed
earlier in patients whose GDM is not well
controlled.
Gestational Diabetes
Clinical Chemistry 59:9 (2013) 1317MODE OF DELIVERY
Gestational diabetes is not an indication for cesarean
section. However, cesarean section is more common in
GDM than in nondiabetic pregnancies. The absolute
rates are dependent upon the criteria used for the diagnosis
of GDM and the prevailing cesarean section rates
in the particular location. In the randomized trials of
identification and treatment of mild gestational diabetes,
cesarean sections were performed in 32% of untreated
vs 31% of treated (27 ) and 34% of untreated vs
27% of treated GDM pregnancies (28 ), which in the
latter study was significantly higher. For example, preeclampsia
is more likely to occur in gestational diabetic
pregnancies than in nondiabetic pregnancies, and its
treatment may require early delivery when the cervix is
not favorable. Cesarean section may result. Macrosomia
is more commonly encountered, by mechanisms
outlined above, and failure to progress in labor because
of disproportion between fetus and pelvis may necessitate
cesarean section. Because the fetus of a diabetic
mother tends to have broader shoulders compared to
its head, shoulder dystocia is more likely at any given
birth weight (62 ). A decision analysis (63 ) led to the
conclusion that if a policy of elective cesarean section
were put in place when the estimated fetal weight is
4500 g, then 3695 cesarean sections would be needed to
prevent 1 case of permanent Erb palsy in nondiabetic
pregnancies, whereas 443 cesarean sections would be
needed for diabetic pregnancies. The ACOG suggests offering
cesarean section without labor when the estimated
fetal weight in a diabetic pregnancy is4500 g (29 ). Pregnant
patients with a history of infant shoulder dystocia in
an earlier delivery,whose estimatedfetalweightis equal to
or greater than that of the previous affected offspring, are
also typically offered cesareans. Another possible cause of
increased cesarean sections in gestational diabetic pregnancies
is the obstetrician’s concern about the possibility
of shoulder dystocia, even when the fetus is not large.
A Canadian study (64 ) found that when obstetricians
were blinded to the diagnosis of mild GDM and
patients were not treated, cesarean sections were
performed more often than in nondiabetic pregnancies
and were associated with macrosomic fetuses.
However, when caregivers knew the diagnosis of
more severe GDM and treated it accordingly, macrosomia
was reduced but cesarean sections were still
performed at a greater rate than in the nondiabetic
population; these cesarean sections were not confined
to the macrosomic fetuses. It could be concluded
that the obstetricians were more likely to
intervene because of their concerns regarding macrosomia
and shoulder dystocia, which were brought
about by the caregivers’ knowledge of the diagnosis
of GDM.