There are risks to crib sleeping just as there are risks to bed sharing! And P.S. - Cosleeping does NOT necessarily mean bed sharing. What any parent hopefully tries to do is make the safest sleep environment possible, whether that's in a crib or in a family bed. And even parents who thought they were being safe have unfortunately had to suffer the loss of a child. Some of those deaths were probably preventable, while some babies would have died of unknown causes whether in a family bed or in a crib down the hall in a separate room.
Do babies die in cribs? You bet they do. That's why it was called "crib death" for so long before it was given the less negative-sounding name "SIDS." Even parents who have tried to be safe have had babies die in cribs by the baby:
- becoming entrapped between the crib slats
- suffocating when cribs collapse inward
- choking on some toy or crib bumper or object left in crib
- stopping breathing and being too far away from the parents (and that "trusty baby monitor") for the parents to notice & do anything about it
- being seriously sick but the parents not being able to tell how feverish or ill the baby is because that baby was down the hall in another room
- dying of unknown causes
So all of these parents with babies who only ever sleep in cribs, you may think you're being safe but it's always important to double and triple check the safety of the crib and bedding because babies still die in cribs (is your crib recalled? assembled correctly? free of excess bedding, chokable objects, strangulation hazards? firm matress? no gaps between mattress & crib sides?).
Do babies die while bedsharing? Yes here, too. Even parents who have tried to be safe have had babies die while sleeping in the same bed with the baby:
- becoming entrapped between the wall and the bed (never cosleep on a couch, waterbed, recliner, etc.)
- suffocating due to excessive blankets, pillows, etc.
- being rolled onto by a severely overtired parent, a parent who sleeps too heavily in general, or a parent who is on medication that makes them drowsy, etc.
- dying of unknown causes
So all parents with babies in the same bed with you, you may think you're being safe but it's always important to double and triple check the safety of the family bed (bed low to the ground to prevent falling out of bed? no gaps between wall and bed? firm mattress surface? minimal bedding?) AND your own levels of awareness while sleeping + your tiredness levels (too tired? drowsy from cold meds? don't cosleep that night! not very aware of your baby in bed in general? don't cosleep then!) because babies still die in bedsharing arrangements.
Historically, yes, mothers and babies are hardwired to share sleep. Biologically, it is very advantageous for parents to share sleep with their babies (promotes safer, lighter sleep which reduces SIDS rates, promotes breastfeeding to ensure good food supply and smaller, more frequent feeding which is healthier in the long run than larger gaps between big meals).
Not every family should cosleep. Not every family should have their baby alone in another part of the house in a crib. And sadly, regardless of whatever your choice, some families will suffer the terrible loss of a child either in a crib or in a family bed. The REAL issue here is that we create the safest sleep environment for our own family based on our unique physiology (for example, I can't sleep well with my baby in a different room, so I get much more restful sleep when cosleeping - my husband feels the same way - but in general we are very aware of where our baby is at all times. On nights where either of us is just exhausted, too tired to be aware, our little guy sleeps in his crib at the foot of our bed!).
N., it's wonderful that you are able to recognizing what sleeping arrangement is most optimal for your baby and your family! Cosleeping safely is a very valid, time-tested choice, and this is well supported by research (http://www.nd.edu/~jmckenn1/lab/intro.html), though the crib manufacturers would never tell you that! ;) Consider, too, that your MIL may have very different sleep than you (and babies with very different temperaments than yours) such that cosleeping was not optimal for her/her children.
Congratulations on becoming a mother and the birth of your son earlier this year!