Most pushchairs are forward facing. Recently the opinion seems to be that rearward facing ones are better as they allow the child to see your face.
I am wondering if this is yet another childcare opinion that has taken hold (perhaps to be later reversed) or if it is an Evidence Based guideline? (And if so does the guidance change at different ages).
USA Stroller = UK Pushchair.
There are three main areas where research informs guidance and design decisions on this type of infant transport. To summarise, there is evidence to support the common practice of rear/inward facing for newborns and switching as they develop.
Newborn vision is limited to short distances in the order of 20-30cm.
Source: Visual Development (babycentre.co.uk, contains references)
They learn to recognise their parents quite early on and until they develop an awareness of object permanence anything they can't see is essentially gone, which we can assume to be fairly distressing. Object permanence was thought to take until age 2 to develop but more recent research suggests babies as young as 4 months understand it.
Young babies are less able to regulate their temperature and a rear facing seat makes it easier for a carer to assess their comfort level.
Historically (as much for engineering reasons as anything else) we had Prams and Pushchairs rather than the all-in-one systems we have today. Learned behaviour passed down through generations is equally likely to drive the common practices of today as any specific evidence or guideline.
Similar patterns and practices are observed in sling users, where newborns face inward and are turned to face outwards as they become more interested in the outside world.
Note: This answer does not apply to Child Car Seats, where evidence supports use of a rear facing seat for as long as possible to minimize injury in a collision.
I don't know of an existing guideline, but I'm familiar with the evidence: there is research showing that babies facing forward have a faster heartbeat, and are less likely to nap - both during walks.
How to interpret this is another question. One interpretation (that I've seen, but personally I don't buy it) is that facing forwards is just stressful - and stress is bad for you - while seeing the parent is calming.
Personally, I find the leap from increased heartbeat to stress to harm to be too much of a stretch. It could just be that facing forwards is more dynamic/stimulating/exciting - and more excitement is not necessarily a bad thing. It will vary per child of course, because some babies like stimulation while others shy away from it.
Depending on how old your child is, it may not be able to focus on your face.
A rearward facing stroller also allows the parent to see the child's face. This means you can spot distress in your child quicker than if you're waiting to hear angry noises from a forward facing stroller. If you're walking your child around outside, it's also much easier to assess whether they're comfortable or being dazzled by sunlight if they're facing backwards. Similar for rain, dust, wind.
Maybe a better reason is that a rear-facing stroller will give better support to your child's head when (as seems inevitable) you run the stroller into a curb - similar to the reasoning behind infant car seats facing backward rather than forward. Once your child is strong enough to hold his or her head up, I suppose that's of lesser importance.
I agree with Ana's answer; a child is likely to be more stimulated by its environment when it's facing the direction of travel. Depending on whether you want your child to be excited or napping may influence your decision. (Or depending on how exciting your face is.)
The research that I have read focused on the level of interaction that occurs when baby is facing the parent. More talking to baby, more interaction on all levels and that this kind of stimulation at the baby carriage age is beneficial as compared to the kind of stimulation facing front. Facing front is not a bad thing, but the thinking is that facing parent is better.
