Nature Neuroscience
Resource https://doi.org/10.1038/s41593-024-01741-0
Methods
Participant
Our participant (E.R.C.) was a healthy 38-year-old primiparous woman 
who underwent in-vitro fertilization (IVF) to achieve pregnancy. Pre-
vious studies reported no observable differences in neural changes 
from prepregnancy to postpregnancy between women who conceived 
naturally versus women who conceived via IVF13, and doing so provides 
a controlled way of monitoring pregnancy status. The participant 
experienced no pregnancy complications (for example, gestational 
diabetes and hypertension), delivered at full term via vaginal birth, 
nursed through 16 months postpartum, and had no history of neu -
ropsychiatric diagnosis, endocrine disorders, prior head trauma or 
history of smoking. The participant gave written informed consent and 
the study was approved by the University of California, Irvine Human 
Subjects Committee.
Study design
The participant underwent 26 MRI scanning sessions from 3 weeks 
before conception through 2 years postpartum (162 weeks), during 
which high-resolution anatomical and diffusion spectrum imaging 
scans of the brain were acquired. Scans were distributed throughout 
this period, including prepregnancy (four scans), first trimester (four 
scans), second trimester (six scans), third trimester (five scans) and 
postpartum (seven scans; Fig. 1c ). The first 6 sessions took place at 
the UCSB Brain Imaging Center (BIC), the final 20 sessions took place 
at the UCI Facility for Imaging and Brain Research (FIBRE). The major-
ity of scans took place between 9 AM and 2 PM, limiting significant 
AM–PM fluctuations49. The MRI protocol, scanner (Siemens 3T Prisma) 
and software (version MR E11) were identical across sites. Each scan -
ner was checked weekly for the duration of the study and passed all 
QC reports indicating no significant alterations in the geometry. T o 
ensure the robustness of the findings, after the final study session, the 
participant completed back-to-back validation scans at UCI and UCSB 
within a 12-h window to assess reliability between scanners. Intraclass 
correlation coefficients (two-way, random effects, absolute agreement, 
single rater) reveal ‘excellent’ test–retest reliability between scanners, 
including ROI-level GMV (ICC = 0.97, 95% CI: 0.80–0.99), ROI-level 
CT (ICC = 0.96, 95% CI: 0.90–0.98), MTL subfield volume (ICC = 0.99, 
95% CI: 0.97–0.99) and ROI-level QA (ICC = 0.94, 95% CI: 0.91–0.97). 
Furthermore, when examining the relationship between gestation 
week and GMV among UCI-only gestational sessions, findings were 
consistent (Supplementary Fig. 12), indicating that site differences 
are highly unlikely to have contributed meaningfully to the observed 
effects. Although not applicable here, we note that having a control 
participant scanned over a similar duration within the same scanner is 
critical for estimating how much variation in the brain can be attributed 
to within-scanner variability.
T o monitor state-dependent mood and lifestyle measures, the 
following scales were administered on each experiment day: Perceived 
Stress Scale50, Pittsburgh Sleep Quality Index 51, State-Trait Anxiety 
Inventory for Adults52 and Profile of Mood States53. Correlation analy-
ses between state-dependent measures, summary brain metrics and 
gestation week revealed little to no relationships. The only exception 
to this was a moderate negative association between global QA and 
state anxiety (Spearman’s correlation (ρ) = −0.65, q = 0.04; baseline—36 
weeks, n = 16). By making this data openly accessible, we encourage a 
more nuanced approach toward exploring mood and lifestyle measures 
in relation to brain changes over pregnancy.
Endocrine procedures
The participant underwent a blood draw (n  = 19; Fig. 1c ) before 
MRI scanning. Sex steroid concentrations were determined via 
ultra-sensitive liquid chromatography–mass spectrometry at the