Methods
We conducted a retrospective cohort study at a single outpatient health
clinic between 2011 and 2018. The study group included healthy women at
24-28 weeks of gestation with one abnormally high value on their OGTT
and a low glucose finding for the 3-hour hypoglycemia analysis
(<60 mg/dl). The control group was comprised of women with
high or normal 180-minute glucose values with one abnormal value in the
OGTT. Excluded from the study were women with a multiple pregnancy,
pre-gestational diabetes, or incomplete medical or obstetrical records.
The Institutional Review Board approved the study and waived informed
consent.
GDM was diagnosed by a two-step approach consisting of a 1-hour 50 g GCT
at 24–28 weeks of pregnancy, followed by a 3-hour 100 g diagnostic OGTT
if the GCT plasma glucose result was ≥140 mg/dL. Women with risk factors
for developing GDM, such as a family history of diabetes in a
first-degree relative, previous GDM, or previous macrosomia, underwent
only diagnostic OGTT. GDM was diagnosed when at least one of the four
OGTT glucose values was abnormally high by the Carpenter and Cousten
criteria14.
Once diagnosed, all women were instructed to self-measure capillary
glucose at least four times daily (fasting and one or two hours
postprandial). The initial clinic visit included counseling by a nurse
expert in diabetes, dietary consultation by a certified dietician, and
consultation with a maternal-fetal medicine specialist. The biweekly
visits were scheduled up to 36 weeks of gestation and weekly from that
stage to delivery. Each visit included dietary consultation, blood
pressure monitoring, urine dipstick test, review of daily glucose
profiles, and decision-making regarding the need for adjusting therapy.
Ultrasound scans for biophysical profiles and estimation of fetal growth
were performed biweekly from 26 weeks of gestation, and non-stress
testing was added at 34 weeks of gestation.
The desired level of glycemic control was defined as mean fasting blood
glucose <90 mg/dl and mean one or two hours postprandial
<140 mg/dL or <120 mg/dl, respectively. Women with
fewer than 50 glucose measurements over the two weeks were not included
in the final analysis. Women who had more than30% abnormally high
values during a 2-week period of glucose monitoring were considered as
having suboptimal glucose control.15 The detection of
suboptimal glucose control led to an intervention aimed at modifying the
diet and encouraging physical activity. Insulin treatment was initiated
when fasting glucose levels were consistently >100 mg after
two weeks of observing a strict diet or when suboptimal glucose control,
as defined above, persisted after 2 weeks of dietary modifications and
physical activity.
The need for induction of labor was determined by the level of glycemic
control and estimated fetal weight. Induction of labor was offered at
38–39 weeks of gestation if the estimated fetal weight (EFW) was
3600-4000 gr or poor glycemic control was documented [defined as?].
Cesarean section was advised when the EFW was >4000 gr or
for obstetrical indications. If the abovementioned criteria were not
fulfilled induction of labor was advocated at 41 weeks of gestation.
Women with one abnormally high OGTT value were divided into two groups.
Women in the study group had a low 180-minute value defined as a plasma
glucose level of ≤60 mg/dl, and those in the control group had a
180-minute glucose value of >60 mg/dl. The following data
were extracted from women’s computerized files and compared between the
two groups: maternal demographics and clinical characteristics, periods
of suboptimal glucose control, the need for insulin to achieve desired
levels of glycemic control, glycemic profile, and obstetrical and
neonatal outcome measures. The primary outcome was the rate of women
with suboptimal maternal glycemic control. The secondary outcomes were
the need for insulin treatment to achieve desired levels of glycemic
control and the presence of obstetrical and neonatal complications,
including mean birthweights, incidence of macrosomia (birthweight more
than the 90th percentile or >4000 gr),
and polyhydramnios (amniotic fluid index >25 cm or a
maximal vertical pocket >8 cm).
Statistical analysis
Between-group comparisons of the study participants’ characteristics
were performed by a 2-tailed Student’s t test for continuous variables,
a Pearson χ2 test for categorical variables, and the Kruskal–Wallis
test for continuous non-normal variables. A P value of less than
or equal to .05 was considered significant. Multivariate logistic
regression assessed the association between the various selected
variables and suboptimal maternal glycemic control. Maternal age,
parity, EFW, and delivery week were taken as continuous variables and
the remaining variables were taken as categorical. All statistical
analyses were performed with R version 3.5.2. (http://www.r-project.org)