This is from Kelly-Mom.com:
Is forceful let-down the problem?
Does your baby do any of these things?
Gag, choke, strangle, gulp, gasp, cough while nursing as though the milk is coming too fast
Pull off the breast often while nursing
Clamp down on the nipple at let-down to slow the flow of milk
Make a clicking sound when nursing
Spit up very often and/or tend to be very gassy
Periodically refuse to nurse
Dislike comfort nursing in general
If some of this sounds familiar to you, you probably have a forceful let-down. This is often associated with too much milk (oversupply). Some mothers notice that the problems with fast letdown or oversupply don't start until 3-6 weeks of age. Forceful let-down runs the gamut from a minor inconvenience to a major problem, depending upon how severe it is and how it affects the nursing relationship.
What can I do about it?
There are essentially two ways you can go about remedying a forceful let-down: (1) help baby deal with the fast flow and (2) take measures to adjust your milk supply down to baby's needs. Since forceful let-down is generally a byproduct of oversupply, most moms will be working on both of these things. It may take a couple of weeks to see results from interventions for oversupply, so try to be patient and keep working on it.
Help baby deal with the fast milk flow
Position baby so that she is nursing "uphill" in relation to mom's breast, where gravity is working against the flow of milk. The most effective positions are those where baby's head and throat are above the level of your nipple. Some nursing positions to try:
Cradle hold, but with mom leaning back (a recliner or lots of pillows helps)
Football hold, but with mom leaning back
Elevated football hold - like the football hold, but baby is sitting up and facing mom to nurse instead of lying down (good for nursing in public).
Side lying position - this allows baby to dribble the extra milk out of her mouth when it's coming too fast
Australian position (mom is "down under", aka posture feeding) - in this position, mom is lying on her back and baby is on top (facing down), tummy to tummy with mom. Avoid using this positioning frequently, as it may lead to plugged ducts.
Burp baby frequently if she is swallowing a lot of air.
Nurse more frequently. This will reduce the amount of milk that accumulates between feedings, so feedings are more manageable for baby.
Nurse when baby is sleepy and relaxed. Baby will suck more gently at this time, and the milk flow will be slower.
Wait until let-down occurs, then take baby off the breast while at the same time catching the milk in a towel or cloth diaper. Once the flow slows, you can put your baby back to the breast.
Pump or hand express until the flow of milk slows down, and then put baby to the breast. Use this only if nothing else is working, as it stimulates additional milk production. If you do this, try to express a little less milk each time until you are no longer expressing before nursing.
Adjust your supply to better match baby's needs
If baby is gaining weight well, then having baby nurse from only one breast per feeding can be helpful.
If baby finishes nursing on the first side and wants to continue nursing, just put baby back onto the first side.
If the second side becomes uncomfortable, express a little milk until you're more comfortable and then use cool compresses - aim for expressing less milk each time until you are comfortable without expressing milk.
Avoid extra breast stimulation, for example, unnecessary pumping, running the shower on your breasts for a long time or wearing breast shells.
Between feedings, try applying cool compresses to the breast (on for 30 minutes, off for at least an hour). This can discourage blood flow and milk production.
If nursing one side per feeding is not working after a week or so, try keeping baby to one side for a certain period of time before switching sides. This is called block nursing.
Start with 2-3 hours and increase in half-hour increments if needed.
Do not restrict nursing at all, but any time that baby needs to nurse simply keep putting baby back to the same side during that time period.
If the second side becomes uncomfortable, express a little milk until you're more comfortable and then use cool compresses - aim for expressing less milk each time until you are comfortable without expressing milk.
In more extreme cases, mom may need to experiment a bit with time periods over 4 hours to find the amount of time per breast that works best.
Additional measures that should only be used for extreme cases of oversupply include cabbage leaf compresses and herbs.
Even if these measures do not completely solve the problem, many moms find that their abundant supply and fast let-down will subside, at least to some extent, by about 12 weeks (give or take a bit). At this point, hormonal changes occur that make milk supply more stable and more in line with the amount of milk that baby needs.
Sometimes babies of moms with oversupply or fast let-down get very used to the fast flow and object when it normally slows somewhere between 3 weeks to 3 months
HTH!
