Pemphigoid gestationis (PG) is a rare, itchy skin eruption that usually happens in the second or third trimester of pregnancy. It often begins with the appearance of very itchy red bumps or blisters on your abdomen and trunk, though it can show up on other parts of your body.

PG is caused by your immune system mistakenly attacking your own skin. It usually goes away on its own within days or weeks after delivery. In rare cases, it can last longer.

PG is estimated to occur in 1 of every 40,000 to 50,000 pregnancies.

Pemphigoid gestationis used to be known as herpes gestationis, but it’s now understood that it has no connection to the herpes virus. There are also other types of pemphigus or pemphigoid skin eruptions, not related to pregnancy.

Pemphigus refers to a blister or pustule, and gestationis means “of pregnancy” in Latin.

With PG, red bumps appear around the belly button and spread to other parts of the body within a few days or weeks. Your face, scalp, palms, and soles of the feet are usually not affected.

After two to four weeks, the bumps turn into large, red, fluid-filled blisters. These bumps can also be called bulla. They can be extremely uncomfortable.

Instead of blisters or bulla, some people develop raised red patches called plaques.

The PG blisters may shrink or go away on their own near the end of your pregnancy, but 75 to 80 percent of women with PG experience a flare-up around the time of delivery.

PG can recur during menstruation or in subsequent pregnancies. Use of oral contraceptives may also bring on another attack.

In rare cases — about 1 in every 100,000 births — PG can appear in newborns.

Pemphigoid gestationis is now understood to be an autoimmune disease. That means that your immune system begins to attack parts of your own body. In PG, the cells that come under attack are those of the placenta.

Placental tissue contains cells from both parents. The cells that have derived from the father may contain molecules that are recognized as foreign by the mother’s immune system. This causes the mother’s immune system to mobilize against them.

Paternal cells are present in every pregnancy, but autoimmune diseases like PG only occur in some cases. It’s not completely understood why the maternal immune system reacts in this way in some cases, and not in others.

But certain molecules known as MHC II that are normally not present in the placenta have been found in women with PG. When a pregnant women’s immune system recognizes these molecules, it launches an attack.

The MHC II-class molecules are responsible for the sticking together of your layers of skin. Once your immune system begins to attack them, it can result in the blisters and plaque that are a main symptom of PG.

One measure of this autoimmune reaction is the presence of a protein now known as Collagen XVII (formerly called BP180).

Another skin eruption known as PUPPP (pruritic urticarial papules and plaques of pregnancy) can resemble pemphigoid gestationis. As the name suggests, PUPPP is itchy (pruritic) and hive-like (urticarial).

PUPPP occurs most often in the third trimester, which is also a common time for PG to appear. And like PG, it most often appears first on the abdomen as itchy red bumps or plaques.

But PUPPP doesn’t usually progress to large, fluid-filled blisters like PG. And unlike PG, it often spreads to the legs and sometimes the underarms.

PUPPP is treated with anti-itch creams and ointments, and sometimes with antihistamine tablets. The rash usually disappears on its own within six weeks after delivery.

PUPPP occurs in about 1 in every 150 pregnancies, making it much more common than PG. PUPPP is also more common in first pregnancies, and in women carrying twins, triplets, or higher order multiples.

If your doctor suspects PG, they may refer you to a dermatologist for a skin biopsy. This involves applying a local anesthetic or freezing spray to a small area of skin and cutting away a tiny sample to be sent to the laboratory.

If the lab finds the signs of pemphigoid under the microscope, they’ll do a further test known as an immunofluorescence analysis that can confirm PG.

Your doctor will also take blood samples to determine the levels of the pemphigoid antigen Collagen XVII/BP180 in the blood. This may help them to assess the disease activity.

If your symptoms are mild, your doctor may prescribe anti-itch creams known as topical corticosteroids. These calm the skin by reducing the level of immune system activity at the site of the blisters.

Over-the-counter allergy drugs (antihistamines) can also be helpful. These include the non-drowsy products:

  • cetirizine (Zyrtec)
  • fexofenadine (Allegra)
  • loratadine (Claritin)

Diphenhydramine (Benadryl) induces drowsiness and is best taken at night. It then serves as a sleep aid in addition to its properties as an itch reliever.

All of these are available over the counter. Generic versions are equivalent in activity to the brand names, and often considerably less expensive.

Always speak to your doctor before taking any medications, even over-the-counter products, during pregnancy.

Home remedies

Your doctor may also suggest home remedies to fight the itch and discomfort of a mild case of PG. These can include:

  • keeping the skin cool with ice or cold compresses
  • staying in a cool or air-conditioned environment
  • bathing in Epsom salt or oatmeal preparations
  • wearing cool cotton clothing

More severe cases

When itching and irritation are more severe, your doctor will likely prescribe oral corticosteroids. As these drugs act by reducing the activity of the immune system, the minimal effective dose must always be used.

Your doctor will take into account the effects on both you and your baby, and keep the dosage and duration of treatment to a minimum.

Immunosuppressive drugs such as azathioprine or cyclosporine may also be used to help reduce the itch and discomfort. Careful monitoring for side effects is needed. This may include:

  • checking blood pressure once or twice a week for the first month of use
  • monitoring kidney function with blood and urine tests
  • monitoring liver function, uric acid, and fasting lipid levels

A 2009 study found that outbreaks of PG blisters in the first or second trimester may lead to adverse pregnancy outcomes.

The study examined the case records of 61 pregnant women with PG from the United Kingdom and Taiwan. The adverse outcomes found in women with early-onset (first or second trimester) PG included:

It’s more common for PG to appear later in the pregnancy. When it occurs in the first or second trimester, the study authors recommend treating it as a high-risk pregnancy with more careful monitoring and supervision.

On the positive side, the study also found that treatment with systemic (oral) corticosteroids doesn’t substantially affect pregnancy outcomes.

Pemphigoid gestationis is a rare skin outbreak usually occurring late in pregnancy. It’s itchy and uncomfortable, but not life-threatening for you or your baby.

When it occurs early in a pregnancy there’s a slight increase in chances for a preterm birth or low birthweight infant. Closer monitoring by your OB-GYN doctor and coordination of treatment with your dermatologist is recommended.

You may want to be in touch with the International Pemphigus and Pemphigoid Foundation, which has discussion groups and peer coaches for people with PG.