Here is the design of a clinical trial:

Official Title: Before the Beginning: Preconception Lifestyle Interventions to Improve Future Metabolic Health

Included conditions:
- Gestational Diabetes

Study Armgroups:
- {'label': 'diet + training', 'type': 'EXPERIMENTAL', 'interventionNames': ['Behavioral: time-restricted eating', 'Behavioral: high intensity exercise', 'Other: Standard Care']}
- {'label': 'controls', 'type': 'ACTIVE_COMPARATOR', 'interventionNames': ['Other: Standard Care']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'time-restricted eating', 'description': 'Participants will be asked to limit the time-window for their daily energy intake to a maximum of 10 hours.', 'armGroupLabels': ['diet + training']}
- {'type': 'BEHAVIORAL', 'name': 'high intensity exercise', 'description': 'Participants will be encouraged to exercise with high intensity 2-3 times per week', 'armGroupLabels': ['diet + training']}
- {'type': 'OTHER', 'name': 'Standard Care', 'description': 'Standard clinical care', 'armGroupLabels': ['controls', 'diet + training']}

Primary Outcomes:
- {'measure': 'Plasma glucose concentration', 'description': 'Plasma glucose concentration after 2 h oral glucose tolerance testing (75 g glucose)', 'timeFrame': 'Gestational week 28'}

Please estimate the sample size based on the assumption: 
The sample size calculation is based on a two-sided t-test with a power of 0.90, a significance level of 0.05, and an expected dropout rate of 10-20%.
Sample size calculation
        The primary outcome of this study is glucose tolerance (after a 2-hour OGTT) in gestational week 28. The HAPO study results63 indicate strong, continuous associations of maternal glucose levels, even below the diagnostic level of GDM with adverse maternal and offspring outcomes. Based on the increasing risk of adverse maternal and offspring outcomes across 2-hour plasma glucose categories with a change of~1âmmol/L, we consider a difference of 1âmmol/L in 2-hour plasma glucose after OGTT between the intervention and control group as clinically relevant. We also used the observed standard deviation (1 SD = 1.3âmmol/L) in 2-hour plasma glucose after OGTT in the HAPO study for the sample size calculations. Calculation of the sample size for a two-sided t-test to detect a difference of 1âmmol/L between the groups, using an SD of 1.3âmmol/L, a power of 0.90 and a significance level of 0.05, yields 37 participants in each group in gestational week 28. To allow for an expected exclusion from the study due to not conceiving within the study period (~50%)64 yielding 74 per group, further drop-out during the study period (10â20%), yielding 93 per group, and to increase statistical power for secondary analyses, we initially wanted to include 260 participants in the trial.
        However, we terminated the inclusion of new participants at 167 participants since we had reached 47 participants in each group who were pregnant in gestational week 12. With this number of participants, we foresee that we will have at least 37 participants in each group in gestational week 28, allowing for up to 20% dropout during pregnancy. We expect more participants who are already included to become pregnant in the upcoming period, which will increase the number of pregnant participants.