A great question. I was told last year by a colleague that there was evidence that they should still be pumping a little, but not as much as baby that is not latching. That makes sense to me because they are going to breast, getting some milk and the breast is getting some stimulation - but probably not as much as without the shield. What was suggested was to have the mother's pump 4 to 6 times per day instead of 8 or more. I would disagree with the advice not to have them pump at all. I have encountered a few things in the past from CBC that I have disagreed with, but generally a good organization. I took their Childbirth Educator course. I have a friend that took their breastfeeding class. I would ask this person for the research to back up what she is saying. I think I heard that this may have been a recommendation from the manufacturer of the shields? But not sure.
A recent review on nipple shields was published in Frontiers in Public Health. It was a very nice review and recommend reading it. The Use of Nipple Shields: A Review. Front Public Health. 2015; 3: 236. 
They reviewed 14 articles: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4607874/
They did not make a specific recommendation on pumping, but did say that anyone using one needs more follow up. Also reviewed this study where they found no differences in hormone levels, but did find reduced milk transfer.
Amatayakul et al. (10) randomly assigned 50 Northern Thai women to one of three groups: group 1 (16/50) breastfed without a thin latex nipple shield, group 2 (16/50) breastfed with a thin latex nipple shield, and group 3 (18/50) wore a thin latex nipple shield but did not breastfeed. At 1 week postpartum, prolactin and cortisol levels, infant suckling time, and milk transfer were measured with and without a nipple shield. Based on blood samples collected before, during, and after the feeding, no significant differences in either hormone levels were found between groups 1 and 2 (prolactin – p = 0.83; cortisol – p > 0.1). Use of the nipple shields when breastfeeding had significantly reduced milk transfer, from a median of 47 g in group 1 to a median of 27 g in group 2, which was likely due to the inhibition of oxytocin release in group 2 mothers (10) (Table ​(Table11).

Anyway, the basic plan I've been sending mother's home with when baby is latching to breast consistently with the NS is to breastfeed on demand. And because most babies have better feedings at night, I encourage them to just breastfeed at night with the NS, and pump at least x 4 during the day when babies are typically sleepier anyway. I tell them it's like an insurance policy. I want them to do this for at least the first 2 to 3 weeks and then come back for pre and post feed weights. That will determine if she can begin to slowly step down on the pumping. If baby is not latching well with NS, then needs to pump at least x 8 per 24 hours. I'm finding more success with this plan long-term because they are less exhausted. We have them track milk production with a log. We evaluate them individually as to whether or not they need to provide the expressed milk they pump, or store it.
We give this to them as a written plan, otherwise they go home, their milk comes in, they think baby is gulping down milk well and they stop pumping because they are busy taking care of a newborn and are tired. Really the baby is doing more swallowing than suckling because she has a high hormone level and probably an oversupply. Then by week 2 their milk supply starts dropping and I get the teary phone call. I think there are some babies who probably do great right away with the NS and mom has an abundant supply and they probably would be fine with no pumping, but I tell my patients that I can't know which babies will do that right away, so think of it like an insurance policy to protect your supply. There's growing evidence that the first few weeks is the time where the body is programming the milk supply for the entire milk yield through the growth and differentiation of prolactin receptors in the breast. It's a critical time for production. At about 2 to 3 weeks also is usually when we begin having them try to take the shield off after about 5 or 10 minutes and try to latch without it. I hope this helps. Would love to hear what other people do too.
Sincerely,
Tricia Shamblin, RN, IBCLC

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