What is Herpes gestationis or pemphigoid gestationis (PG)

Herpes gestationis or pemphigoid gestationis (PG) is a bullous (characterized by blistering, such as a second-degree burn) disease developing in association with pregnancy. It is believed to be an autoimmune disorder. It occurs during pregnancy, typically in the second or third trimester, and/or immediately following pregnancy. It was originally called herpes gestationis because of the blistering appearance, although it is not associated with the herpes virus. Diagnosis of PG becomes clear when skin lesions progress to tense blisters during the second or third trimester. PG typically starts as a blistering rash in the navel area and then spreads over the entire body. It is sometimes accompanied by raised, hot, painful welts called plaques. After one to two weeks, large, tense blisters typically develop on the red plaques, containing clear or blood-stained fluid. PG creates a histamine (compound involved in local immune responses) response that causes extreme relentless itching (pruritus). PG is characterized by flaring and remission during the gestational and sometimes post partum period. Usually after delivery, lesions will heal within months, but may reoccur during menstruation.

Pemphigoid gestationis (PG) is a pregnancy-associated, autoimmune skin disorder. It usually begins abruptly during the 2nd or 3rd trimester of pregnancy, but it can begin at any time during pregnancy. Signs and symptoms often include the sudden formation of very itchy, red bumps and/or blisters on the abdomen and trunk, which may then spread to other parts of the body. Unrelenting itchiness (pruritus) often interferes with daily activities.[1] Symptoms may improve at the end of pregnancy, but flares may occur during, or right after, delivery. While PG usually goes away on its own within weeks to months after delivery, it has been reported to persist for years in some cases.[1] PG is caused by a woman’s immune system producing autoantibodies and mistakenly attacking her own skin, but the trigger for autoantibody production is poorly understood.[1] Treatment aims to relieve itching and prevent blister formation, and may involve the use of topical corticosteroids, oral corticosteroids, and/or oral antihistamines.[2] The lowest effective dose of medication should be used in order to minimize the risk to the mother and fetus.[3] The disorder may recur at a later time such as when menstruation resumes; with use of oral contraceptives; and/or during subsequent pregnancies.[1][2]

In most women with pemphigoid gestationis (PG), the condition begins abruptly as an extremely itchy, hive-like rash during mid to late pregnancy (during the 2nd or 3rd trimester). It often begins with red bumps around the abdomen and trunk, and then spreads to other parts of the body within days to weeks. Large, fluid-filled blisters may form on the affected areas of skin. Some people with PG do not develop blisters, but instead have large, raised patches (plaques).[1][2]

Symptoms may improve or go away on their own towards the end of the pregnancy. However, most women experience a “flare” around the time of delivery. In most cases, symptoms go away again days after giving birth, but in some women the condition persists for weeks, months, or even years. The condition may occur again when menstruation resumes, with the use of oral contraceptives, or during future pregnancies.[1][2]

Some babies of women with PG grow less than expected during pregnancy (small for gestational age) and/or are born before their due date (prematurely).[1][3] While not common, some babies of women with PG are born with a rash similar to that seen in women with PG, but it typically goes away without treatment within a few weeks.[3]

This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
https://rarediseases.info.nih.gov/diseases/6497/pemphigoid-gestationis