Long-term association of pregnancy and maternal brain structure: the Rotterdam Study

Investigating the influence of oral contraceptive pill use on multiple sclerosis risk using UK Biobank data

OBJECTIVE

To investigate the association between oral contraceptive (OC) pill use and the risk of developing multiple sclerosis (MS), attempting to address the limitations present in previous studies that produced conflicting results.

DESIGN

A population-based cohort study using data from the UK Biobank.

PATIENTS

The study included 181,058 women of white ethnicity born in England between 1937 and 1970, among which 1,131 had an MS diagnosis.

INTERVENTION

Oral contraceptive use, considering the self-reported age of initiation and discontinuation. The exposures of interest include the following: ever-use, current use, duration of current use in years, and age and year at initiation.

MAIN OUTCOME MEASURES

Multiple sclerosis diagnosis (International Classification of Disease, 10th revision: G35) was used as an outcome of interest, and the associations with the exposures of interest were investigated using marginal structural models with a time-to-event approach. To adjust for confounding, we included in the models several variables, including MS polygenic risk score, education level, parity, smoking, fertility problems, obesity, and mononucleosis. We further aimed to evaluate the influence of parity using a mediation analysis.

RESULTS

The association of both ever and current OC use did not result in a statistically significant MS hazard increase (ever vs. never-users, hazard ratio [HR] = 1.30 [95% confidence interval {CI}: 0.93,1.82]; current vs. never-users, HR = 1.35 [95% CI: 0.81, 2.25]). However, we highlighted parity as an effect modifier for this association. In nulliparous women, ever and current use resulted in a significant twofold and threefold MS hazard increase (HR = 2.08 [95% CI: 1.04, 4.17] and HR = 3.15 [95% CI: 1.43, 6.9]). These associations were supported by significant MS hazard increases for a higher duration of current use and for an earlier age at initiation. We further highlighted genetic MS susceptibility as another effect modifier, as a stronger OC-MS hazard association was found in women with a low MS polygenic risk score.

CONCLUSION

Our findings highlighted how the association between OC use and MS varies on the basis of individual characteristics such as parity and genetic MS susceptibility. Importantly, current use in nulliparous women was found to be associated with a threefold increase in MS hazard. We acknowledge the need for cautious causal interpretation and further research to validate these findings across diverse populations and OC types.

Parenthood status and plasma oxytocin levels predict specific emotion perception abilities

Superior recognition of positive emotional facial expressions compared to negative expressions is well established. However, it is unclear whether this superiority effect differs between non-parents and parents, for whom emotion perception (EP) is an indispensable skill. Although EP has been shown to be modulated by the neuropeptide oxytocin, a central factor in the development of parental care, very little research has addressed the relationship between EP skills, the transition to parenthood, and plasma oxytocin levels. In the present study, we assessed EP abilities with a test battery and measured plasma oxytocin in 77 non-parent and 79 parent couples and applied structural equation modelling to the data. The results showed increased happiness perception abilities in both parents and individuals with elevated oxytocin levels. Furthermore, non-parents showed superior abilities to recognise anger expressions. No significant associations were found regarding the perception of other basic emotion categories or with a general EP factor. The findings are consistent with previous research indicating that elevated oxytocin levels are associated with enhanced EP abilities. They also extend the existing literature by demonstrating that mothers and fathers, regardless of their oxytocin levels, exhibit increased EP superiority.

Enduring maternal brain changes and their role in mediating motherhood's impact on well-being

Parenthood, particularly motherhood, is known to impact the structure and function of the brain in the short term, but the long-term effects of parenthood and their impacts on well-being are still poorly understood. This study explores the potential longer-term associations between parenthood and the brain, parenthood and well-being, and the potential role of brain modifications in influencing mothers' well-being. Using data from the UK Biobank, which includes brain imaging information from individuals aged 45-82 at the MRI scanning, we discovered differences in brain structure between mothers and non-mothers, with mothers exhibiting widely distributed higher gray matter density, particularly strong in frontal and occipital regions. No brain changes were observed in fathers. Parents reported a higher sense of life's meaning compared to their childless counterparts. Gray matter changes did not mediate the relationship between motherhood and well-being. This suggests that the alterations in gray matter associated with motherhood do not play a deterministic role in shaping long-term changes in well-being.

Protective role of parenthood on age-related brain function in mid- to late-life

The experience of parenthood can profoundly alter one's body, mind, and environment, yet we know little about the long-term associations between parenthood and brain function and aging in adulthood. Here, we investigate the link between number of children parented (parity) and age on brain function in 19,964 females and 17,607 males from the UK Biobank. In both females and males, increased parity was positively associated with functional connectivity, particularly within the somato/motor network. Critically, the spatial topography of parity-linked effects was inversely correlated with the impact of age on functional connectivity across the brain for both females and males, suggesting that a higher number of children is associated with patterns of brain function in the opposite direction to age-related alterations. These results indicate that the changes accompanying parenthood may confer benefits to brain health across the lifespan, highlighting the importance of future work to understand the associated mechanisms.

Association of Cumulative Lifetime Exposure to Female Hormones With Cerebral Small Vessel Disease in Postmenopausal Women in the UK Biobank

BACKGROUND AND OBJECTIVES

Rates of cerebrovascular disease increase after menopause, which is often attributed to the absence of hormones. It remains unknown whether the cumulative exposure to hormones across a female person's premenopausal life extends the window of cerebrovascular protection to the postmenopausal period. To investigate this, we examined the relationship between lifetime hormone exposure (LHE) and cerebral small vessel disease in more than 9,000 postmenopausal women in the UK-Biobank.

METHODS

The cohort consisted of women (aged 40-69 years) who attended one of 22 research centers across the United Kingdom between 2006 and 2010. Women were excluded if they were premenopausal when scanned, had missing reproductive history data, self-reported neurologic disorders, brain cancer, cerebral vascular incidents, head or neurologic injury, and nervous system infection. Endogenous LHE (LHEEndo) was estimated by summing the number of years pregnant (LHEParity) with the duration of the reproductive period (LHECycle = age menopause - age menarche). Exogenous LHE (LHEExo) was estimated by summing the number of years on oral contraceptives and hormone replacement therapy. Cerebral small vessel disease was determined by estimating white matter hyperintensity volume (WMHV) from T2-fluid-attenuated inversion recovery brain MRI (acquired between 2014 and 2021), normalized to intracranial volume and log-transformed. Multiple linear regressions were used to assess the relationship between LHEEndo on WMHV adjusted for age, cardiovascular risk factors, sociodemographics, and LHEExo.

RESULTS

A total of 9,163 postmenopausal women (age 64.21 ± 6.81 years) were retained for analysis. Average LHEEndo was 39.77 ± 3.59 years. Women with higher LHEEndo showed smaller WMHV (adj-R 2 = 0.307, LHEEndo β = -0.007 [-0.012 to -0.002], p < 0.01). LHEParity and LHECycle were independent contributors to WMHV (adj-R 2 = 0.308, p << 0.001; LHEParity β = -0.022 [-0.042 to -0.002], p < 0.05; LHECycle β = -0.006 [-0.011 to -0.001], p < 0.05). LHEExo was not significantly related to WMHV (LHEExo β = 0.001 [-0.001 to 0.002], p > 0.05).

DISCUSSION

Women with more prolonged exposure to endogenous hormones show relatively smaller burden of cerebral small vessel disease independent of the history of oral contraceptive use or hormone replacement therapy. Our results highlight the critical role endogenous hormones play in female brain health and provide real-world evidence of the protective effects premenopausal endogenous hormone exposure plays on postmenopausal cerebrovascular health.

Conceiving complexity: Biological mechanisms underpinning the lasting effect of pregnancy on multiple sclerosis outcomes

Multiple sclerosis (MS) is an autoimmune, demyelinating disease with the highest incidence in women of childbearing age. The effect of pregnancy on disease activity and progression is a primary concern for women with MS and their clinical teams. It is well established that inflammatory disease activity is naturally suppressed during pregnancy, followed by an increase postpartum. However, the long-term effect of pregnancy on disease progression is less understood. Having had a pregnancy before MS onset has been associated with an older age at first demyelinating event, an average delay of 3.4 years. After MS onset, there is conflicting evidence about the impact of pregnancy on long-term outcomes. The study with the longest follow-up to date showed that pregnancy was associated with a 0.36-point lower disability score after 10-years of disease in 1830 women. Understanding the biological mechanism by which pregnancy induces long-term beneficial effects on MS outcomes could provide mechanistic insights into the elusive determinants of secondary progression. Here, we review potential biological processes underlying this effect, including evidence that acute sex hormone exposure induces lasting changes to neurobiological and DNA methylation patterns, and how sustained methylation changes in immune cells can alter immune composition and function long-term.

The Neuroanatomy of Pregnancy and Postpartum

Pregnancy and giving birth are exceptional states in a woman's life for many reasons. While the effects of pregnancy and childbirth on the female body are obvious, less is known about their impact on the female brain, especially in humans. The scientific literature is still sparse but we have identified 12 longitudinal neuroimaging studies conducted in women whose brains were scanned before pregnancy, during pregnancy, and/or after giving birth. This review summarizes and discusses the reported neuroanatomical changes during pregnancy, postpartum, and beyond. Some studies suggest that pregnancy is mainly associated with tissue decreases, and a few studies suggest that this tissue loss is mostly permanent. In contrast, the majority of studies seems to indicate that the postpartum period is accompanied by substantial tissue increases throughout the entire brain. Future research is clearly warranted to replicate and extend the current findings, while addressing various limitations and shortcomings of existing studies.