4 to 6 month old baby fell asleep in car seat, should I move her to crib?

What the evidence says

Yes - once you're at your destination, gently move your sleeping baby to a crib, cradle or bassinet on her back. The Canadian Paediatric Society's Caring for Kids guidance says that if your baby falls asleep in a car seat or stroller, she should be moved to a proper sleep space when you arrive. This applies to naps and nighttime alike, not just long car rides.

The concern isn't the car seat itself while driving - it's essential and safe for travel. The issue is the semi-reclined, angled position, which can let a young baby's chin drop toward her chest and narrow her airway, particularly because babies younger than 4 months have less head and neck control and may not be able to reposition themselves out of a risky position. Studies measuring oxygen levels have found that some healthy full-term infants experience brief dips in oxygen saturation while positioned in car seats, and rare but real infant deaths have occurred when babies were left sleeping unattended in car seats, especially if the seat tips over.

This is why car seats, swings, strollers and similar 'sitting devices' are not recommended for routine sleep at home. The safest sleep setup for the first 6 months is a firm, flat crib, cradle or bassinet in your room, with baby on her back and nothing soft inside. If you're out and about and she's napping in the stroller or car seat, it's fine short-term, but try to transfer her to a flat surface as soon as it's practical and safe to do so.