2 nature portfolio  |  reporting summary April 2023 
Data
Policy information about availability of data
All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: 
- Accession codes, unique identifiers, or web links for publicly available datasets 
- A description of any restrictions on data availability 
- For clinical datasets or third party data, please ensure that the statement adheres to our
 policy 
 
The dataset consists of 26 MRI scans (T1w, T2w, and diffusion scans) alongside state-dependent measures and serum assessments of ovarian sex hormones for each 
session. The data is publicly available on https://openneuro.org/datasets/ds005299.
Research involving human participants, their data, or biological material
Policy information about studies with human participants or human data. See also policy information about sex, gender (identity/presentation), 
and sexual orientation and race, ethnicity and racism.
Reporting on sex and gender Our study focused on a single female participant to explore how pregnancy shapes the human brain.
Reporting on race, ethnicity, or 
other socially relevant 
groupings
The subject was white.
Population characteristics This was a precision imaging study of one 38-year old primiparous woman. 
Recruitment Our participant (corresponding author E.R.C.) was a healthy primiparous woman who underwent in-vitro fertilization (IVF) to 
achieve pregnancy. The project was conceived by E.R.C. and she wished to use herself as the participant, as has been done in 
previous "dense-sampling" studies (cf. Poldrack et al., 2015; Pritschet et al., 2020).
Ethics oversight The participant gave written informed consent and the study was approved by the University of California, Irvine Human 
Subjects Committee.
Note that full information on the approval of the study protocol must also be provided in the manuscript.
Field-specific reporting
Please select the one below that is the best fit for your research. If you are not sure, read the appropriate sections before making your selection.
Life sciences Behavioural & social sciences  Ecological, evolutionary & environmental sciences
For a reference copy of the document with all sections, see nature.com/documents/nr-reporting-summary-flat.pdf
Life sciences study design
All studies must disclose on these points even when the disclosure is negative.
Sample size We used precision imaging to deeply-phenotype, densely-sample an individual over the gestational window. As this study was the first of it's 
kind, our sample size was an N=1 design. Although this limits the generalizability of our findings, this project serves as a proof-of-concept, 
showcasing the value and feasibility of studying a woman's brain during the transition to motherhood.
Data exclusions no history of neuropsychiatric diagnosis, endocrine disorders, prior head trauma or history of smoking
Replication This is the first study of it's kind; therefore, there are no study replications as of yet. However, to reproduce our results internally across 
software packages, we also ran the T1w data through the longitudinal FreeSurfer cortical thickness pipeline (Dale et al., 1999), which 
corroborated our finding that gray matter volume declines throughout gestation (e.g., successful internal replication). This pattern of results 
not only held across software packages, but also brain parcellations (e.g., Schaefer 400-cortical atlas and Desikan-Killiany cortical atlas).
Randomization This was an observational study design, and therefore not randomized. 
Blinding For medial temporal lobe segmentation, scans were randomized and segmentation was performed in a random order, blind to pregnancy 
stage. No other blinding was applicable, given the observational study of brain changes in response to advancing gestational week.
Reporting for specific materials, systems and methods