Irregularly pigmented patches may appear on the face and neck, the “chloasma” of pregnancy. It is uncertain whether this occurs as a direct result of increased melanocyte stimulating hormone (MSH) during pregnancy or is due to the indirect stimulation of an increase in MSH by oestrogen and progesterone.
It usually subsides following delivery. Other pigmentary changes occur which are not restricted to the head and neck, but disappear after pregnancy. There may be some physiological enlargement of the thyroid gland with a corresponding increase in blood flow, but treatment is not required and complete resolution is usual.
Some pigmentation is normal and will resolve after the pregnancy. Patchy pigmentation can occur on the face, particularly if you have pale skin and are exposed to direct, hot sunlight. It is wise to enjoy good weather with the sue of shade in the hotter parts of the day so avoid this problem, which goes away after the baby is born.