mother is associated with an increased risk of shoulder
dystocia compared to the risk in a similar-weight fetus
of a nondiabetic mother, normalization of maternal
glucose is the most important means of prevention of
this problem. However, such efforts are not always successful, and large babies are sometimes born to mothers whose GDM is well controlled. Therefore periodic
ultrasound imaging of the fetus is used to estimate fetal
weight and growth trajectory. Caution should be exercised in interpreting ultrasound fetal weight estimations because the range of error is relatively wide. One
series of investigations has demonstrated the successful
use of ultrasound estimates of fetal growth trajectories
to determine which GDM mothers may or may not
benefit from insulin treatment with (57) or without
(58) increased fasting glucose concentrations.
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.