Hi,
I just had my 36th week check up and I asked the nurse the exact same question. Apparently it is because they need a few pads to clear any amniotic fluid, blood, etc., from the area during labour and then again after the baby is born to clean the area of the lochia (afterbirth bleeding). They prefer to use the non-adhesive one as this does not stick to our skin when they wipe the area clean. Once the baby is born the nurses will check on you frequently and periodically before they send you to rest in the ward, so again they prefer for us to use the non-adhesive pads so it is easier for them to check on the discharge and change the pads. Once we are back in the wards they will check on us less frequently and then we can use the adhesive pads if we prefer. Hope this is helpful, otherwise I would as your nurse to explain it to you at your next visit.
Regards,
Sherinna