The yellowing of older leaves is pretty common on most houseplants as they occasionally shed the old while growing new foliage. So if the leaves that are turning yellow are the oldest ones, near the bottom of the stems not the ends, it might just be this natural process. If the yellowing leaves are more numerous and are happening over the entire plant the first thing to consider is the watering. Plants will shed more of the older growth if they are drying up in between soakings. When water isn’t abundant the plant sheds some of the leaves in order to preserve the new growth.
Leaves that go yellow are also a sign of over-watering or poor drainage, however. Pothos do best when allowed to go slightly dry (but not wilting) between waterings. If your soil has been kept constantly wet that causes root rot which leads to yellowing leaves.
The other thing that can affect indoor plants at this time of year is cold drafts from being too close to a cold window, and hot drafts from a heating unit too near the plant.
To figure things out the first thing to do is to tip the plant out of the pot. If the plant has white roots that means it probably isn’t root rot in that rotting roots are tan and brown. If the plant is very root bound, with congested roots that circle around and around in the pot, it’s time to put the plant in a new pot with new soil. (Note: don’t put any rocks or shards at the bottom of the pot – it’s the holes in a pot that are for drainage and other debris is bad for plants!)
If the roots are healthy and not too crowded, decide if you’ve been watering well enough – soak the entire root ball well every time you water but don’t let the plant sit in a saucer of water after it has gotten well hydrated. Don’t bother “misting” the plant – that does little to raise humidity and causes leaf-spot fungi.
Pick off the worst of your yellow leaves so you can monitor if the problem is continuing. You can fertilize the plant sometime in March when the days are getting longer – use fertilizer according to directions.