Su Yang ,

You can check the following MRI datasets, which I reckon (may) have fetal brain datasets as well:

- https://openfmri.org/dataset/

- http://mridata.org/list

- https://www.oasis-brains.org/#data

- https://fastmri.med.nyu.edu/

- https://www.med.unc.edu/psych/research/niral/download/download-data/

- https://neurodata.io/mri/

- https://openneuro.org/

- https://www.neuroconnlab.org/data/

- https://brain-development.org/

Hope that helps.

http://fetalmri.org/index.html?B30