Study design and patient selection.
The protocol of this prospective case-control study was approved by the hospital ethics committee, and written informed consent was obtained from each participant before participation in the study. All phases of the study were conducted based on the universal ethical principles of the Declaration of Helsinki. The study was conducted between July and December 2019 at the Department of Perinatology, Zekai Tahir Burak Women’s Health and Research Hospital, Ankara, Turkey.
A total of 80 participants were recruited for the study, 40 of whom were diagnosed with GDM and 40 healthy pregnant women with the same gestational age served as the control group. With an effect size of d=0.5, a margin of error of 5%, and a power of 80% (n1:30, n2:30), at least 60 samples were deemed adequate by the power analysis performed with the G*Power 3.0.10 program. All participants were between 28 and 39 weeks of gestation. All demographic and clinical characteristics were obtained from medical records. Gestational age was confirmed using first trimester sonographic dating. GDM was diagnosed according to the criteria of the American College of Obstetricians and Gynecologists (ACOG) guidelines in a two-stage testing procedure at 24 to 28 weeks of gestation [1]. After a positive 50g-one-hour oral glucose challenge test (one-hour glucose level ≥ 140 mg/dl), the diagnosis was made if two or more glucose levels were above the normal range on the 100 g-three-hour oral glucose tolerance test (fasting glucose level: 95 mg/dl; one-hour glucose level: 180 mg/dl; two-hour glucose level: 155 mg/dl; three-hour glucose level: 140 mg/dl).
Exclusion criteria were abnormal prenatal screening results in the first and/or second trimester, multiple pregnancies, a history of coexisting chronic systemic disease, gestational diabetes and other abnormalities of glucose metabolism, pregnancy complications such as gestational hypertension, placental abruption, fetal growth restriction, premature rupture of membranes, and chorioamnionitis. Fetuses with congenital or chromosomal abnormalities were not included in the study. In addition, participants who had a single high glucose level on 100g OGTT were not included in the control group because some of them may have had insulin resistance or impaired glucose metabolism. A total of 20 individuals in both groups were excluded because of obstetric complications that developed during follow-up.
Ultrasound and Doppler Measurements All sonographic examinations were performed transabdominal using the Voluson 730 Expert sonography unit (GE Healthcare, Milwaukee, WI) with a 3.5-MHz convex transducer by a single investigator with 10 years of experience in obstetric sonography who was blinded to all clinical parameters. Sonographic assessment of fetal anatomy, maximal measurement of deepest vertical amniotic fluid (MVP) pocket, fetal biometry, estimated fetal weight (EFW), and umbilical artery Doppler measurements (umbilical artery RI, resistance index; PI, pulsatility index; S/D, systolic/diastolic ratio) were performed according to the guidelines of the International Society of Ultrasound in Obstetrics and Gynecology and the Institute of Ultrasound in Medicine.