Here is the design of a clinical trial:

Official Title: Randomised Controlled Trial of Gestational Treatment With Ursodeoxycholic Acid Compared to Metformin to Reduce Effects of Diabetes Mellitus

Included conditions:
- Gestational Diabetes

Study Armgroups:
- {'label': 'Metformin', 'type': 'ACTIVE_COMPARATOR', 'description': 'Oral 1000 mg BD', 'interventionNames': ['Drug: Metformin']}
- {'label': 'Ursodeoxycholic acid', 'type': 'EXPERIMENTAL', 'description': 'Oral 500 mg BD', 'interventionNames': ['Drug: Ursodeoxycholic Acid']}

Interventions:
- {'type': 'DRUG', 'name': 'Metformin', 'description': 'Patients will be randomized to each intervention using minimisation:\n\n* BMI category (Overweight/Obese),\n* Previous history of GDM,\n* Disease severity (baseline fasting glucose ≤6.2 or \\>6.2),\n* Recruitment centre', 'armGroupLabels': ['Metformin']}
- {'type': 'DRUG', 'name': 'Ursodeoxycholic Acid', 'description': 'Patients will be randomized to each intervention using minimisation:\n\n* BMI category (Overweight/Obese),\n* Previous history of GDM,\n* Disease severity (baseline fasting glucose ≤6.2 or \\>6.2),\n* Recruitment centre', 'armGroupLabels': ['Ursodeoxycholic acid']}

Primary Outcomes:
- {'measure': 'Glycaemic control', 'description': 'Maternal fasting glucose concentration in blood sample', 'timeFrame': 'Gestational week 36'}

Please estimate the sample size based on the assumption: 
Significance level not explicitly stated, 90% power, 18% withdrawal rate, SD 0.6 mmol/L, correlation between repeated measures 0.46
Sample size {14}
        A study size of 158 participants will provide sufficient statistical power to detect a 6% reduction of 0.304Â mmol/L in maternal fasting glucose at 36Â weeks, while allowing for a 18% withdrawal rate (complete data on 130 women).
        Based on data from the UPBEAT study [54], we anticipate a mean of 5.06Â mmol/L, reduced to 4.756 in the intervention group (6% reduction), SD 0.6Â mmol/L, correlation between repeated measures 0.46. Complete data on 130 subjects (65 per arm) will give approximately 90% power to detect a difference in maternal fasting glucose at 36Â weeks of 6% (from 5.06 to 4.75Â mmol/L).
        The 6% reduction is based on a previous study that reported differences with UDCA treatment for nonalcoholic fatty liver disease (NAFLD) in a population of similar body mass index and age to our study group [55]. This difference in glucose concentration is considered clinically relevant as it is equivalent to the difference in glucose categories between which differences in LGA, primary caesarean section, cord blood serum C-peptide levelâ>â90th centile, and clinical neonatal hypoglycemia were evident in the HAPO study [1].