The maternal brain undergoes a major or minor volume resizing of its gray matter, primarily on the temporal-parietal area and in the division of the two cerebral hemispheres, during the weeks before delivery and up to two years after delivery. This process doesn’t mean the loss of functions or brain capacity; on the contrary, it's a process of 'neuronal selection and potentiating of connections, 'which means the brain is reorganizing and strengthening specific neural pathways, leading to cognitive and behavioral modifications that will appear and disappear simultaneously according to the stage of gestation. The brain’s structure changes as estradiol release peaks, promoting emotional lability, irritability, sensitivity to intense emotions, and the nesting phenomenon. Pregnant women recognize their baby as a more vulnerable organism, which can increase feelings of worry, anxiety, and frequent fears.

In the early weeks of pregnancy, motor and sensory functions remain stable. However, over time, symptoms like nausea, frequent urination, constipation, sleep disturbances (which can impact cognitive functions and perception), and changes in eating patterns may arise. These symptoms increase the risk of anxiety, depression, poor coping strategies, and feelings of limited social support, which may also be linked to stress hormone release, affecting attention and memory. Additionally, the physical changes of pregnancy can impact self-esteem and self-concept, leading to feelings of unfamiliarity with oneself and doubts about personal worth and others' affection.

During the second and third trimesters of pregnancy, the limbic system, which is responsible for processing emotions and memory; the orbitofrontal cortex, which is involved in decision-making and emotional responses; and parts of the prefrontal cortex, which is responsible for complex cognitive behavior, play a crucial role in the pregnant woman’s overall functioning. Neural circuits in these areas process and store sensory information more effectively, enhancing learning, responsiveness to environmental stimuli, and coping strategies for discomfort. Emotional experiences related to pregnancy boost associative attention. As birth approaches, functions like selective attention, short-term memory, proprioception, planning, and information processing improve due to increased activity in the precuneus and cingulate gyrus.

Lastly, in postpartum (or fourth trimester), there’s an increase in locus of control, divided attention, directed attention, and planning. However, emotional changes, adjustment disorders, socialization difficulties, and heightened perfectionism may arise and be a risk factor for developing “baby blues” or postpartum depression due to increased frontal lobe activity as the brain strives for cognitive, emotional, and social balance. Despite these challenges, it's important to remember that pregnancy and postpartum do not solely lead to adverse emotional outcomes; they also foster adaptive emotions such as joy, pride, hope, excitement, empathy, and attachment, which are crucial for a positive postpartum experience.

The surrogate’s brain has a crucial role in the integrality of the fetus's development. Some studies indicate maternal stress due to hormonal peaks and excessive release of serotonin, noradrenaline, and dopamine affects the limbic system and hypothalami-pituitary-adrenal axis function. This results in risks of complications like Intrauterine Growth Restriction (IUGR), Small for Gestational Age (SGA), and Low Birth Weight (LBW)). They are risk factors for neurocognitive development in infants and may also indicate potential future deficits in attention, executive functions, and processing speed during childhood.