The study was conducted in a tertiary hospital in southern
Thailand which is the referral center for diabetes care. Sample size
was calculated for two independent samples, intervention group and
control group. The primary outcomes of interest were fasting and
postprandial blood glucose, and hemoglobin A1c. They were each
measured on a continuous scale. Sample size per group was 2c/delta2
+1, where delta was the standardized effect size12
. Delta was the
value of mean differences of the experimental group and control
group divided by the common standard deviation. A two-sided test of
0.05 significant levels was employed. Power for the study was set at
80%. From a pilot study, delta was 0.7. Calculated sample size per
group was 85. Then, the total sample size in this study was 170.
Inclusion criteria for recruitment of participants were: 1) pregnant
Thai women diagnosed with GDM A1 with 24–30 weeks gestational
age, 2) having fasting blood glucose lower than 105 mg/dl, 3) having
postprandial blood glucose lower than 120 mg/dl, 4) not receiving
insulin therapy for glycemic control, and 5) having no serious
complications such as gestational hypertension, preeclampsia, preterm labor, or other serious health problems