Abstract
<jats:p>Pregnancy and the postpartum period, though often joyful, result for around 1 in 5 women in serious mental health challenges. Importantly, these challenges could ripple beyond the mother and affect her child. This thesis found that whether and how maternal stress reaches the child may depend on context, caregiving, and biology. American pregnant women worried more about the period after birth than Dutch women, reflecting the importance of cultural context. After birth, acute maternal stress did not trigger stress in the infant, but lower-quality caregiving went hand in hand with more infant crying and physiological stress. Surprisingly, stress hormones in breast milk were linked to longer infant sleep after feeding, offering reassurance that some fluctuations in milk stress do not negatively affect infant behavior. Together, these findings show that perinatal stress affects infants in ways that are rarely straightforward, urging a more nuanced understanding of how maternal wellbeing reaches children.</jats:p>