My 12 day old baby seems quite constipated and only pooing once a day for the past three days and it has been coming out green and yellow. Baby has just done a poo after hard pushing and it come out dark green followed by a bit of yellow? Baby seems sleepier than normal today however did have a bad night as I think baby has reflux?
That looks very solid for new born poo (colour wouldn't worry me too much but consistency would as they should only have had milk going in). Apart from sleepy, how do they seem in themselves? I wouldn't risk leaving a 12 day old baby with any concern, however small. A doctor will never mind reviewing a tiny baby to put your mind at rest.
Just looked at that link posted above and it would seem formula fed babies can have more solid poo, so if that consistency is similar to what baby has passed previously then I wouldn't worry about that (disclaimer I have only had breast fed babies and the nappy contents I have seen of formula fed babies has been loose so I was unaware it could be more solid, so please seek medical advice if you are at all concerned as baby is so little).