Does pregnancy trigger melasma?

A treatment agreement for dark patches may name pregnancy as a cause, a timing issue or a reason to wait. Check each of those words against the sources before you rely on them.
Is pregnancy really tied to melasma?
my.clevelandclinic.org says: "Melasma is sometimes called the “mask of pregnancy” because it frequently affects pregnant women." The nickname alone points to the connection. For the mechanism, www.aad.org lists pregnancy and says: "An increase in the hormones estrogen and progesterone, which occurs during pregnancy, is thought to trigger melasma." The www.aad.org page on melasma causes carries that sentence in full.
The wording to double-check in a pitch
"Frequently affects" and "is thought to trigger" are measured phrases. A pitch that says pregnancy causes melasma, or that melasma always follows it, has dropped the hedge the sources kept.
DermNet's topic page on melasma is a general reference on the condition to read beside the two sentences above. For any other claim in a pitch, ask which source it comes from.
For a wider view of skin concerns, see Harvard Health's skin care guide for aging skin, which addresses age spots, wrinkles and undereye bags. www.aad.org also publishes advice on making melasma less noticeable.
What to ask for in writing
Ask for the treatment plan to state how pregnancy affects it, and to name the source the provider relies on for that position. A reader in Ann Arbor, Michigan who gets that answer in writing can compare it against the two sentences above.