Pemphigoid gestationis: the itchy blistering rash of pregnancy

The British Association of Dermatologists (BAD) describes pemphigoid gestationis as a rare skin blistering disorder associated with pregnancy, usually appearing in the second and third trimesters with an itchy rash that develops into blisters. It was previously known as herpes gestationis, but the name was changed because it has nothing to do with the herpes virus and, unlike herpes, does not spread. DermNet describes it as a rare, pregnancy-associated autoimmune blistering skin condition, with onset typically between 13 and 40 weeks or in the immediate postpartum period.

It is an autoimmune disease: the BAD says the mother's immune system reacts against her own skin, causing it to split and form blisters. Current understanding is that small parts of placental tissue enter the mother's bloodstream and activate antibodies that attack the skin, and DermNet says the placenta, not the skin, appears to trigger the response. The BAD says female hormones, particularly oestrogen, are thought to aggravate it. It does not run in families, but there is a link with other autoimmune conditions such as thyroid disease and pernicious anaemia.

Itching is common, and the BAD says the rash often starts around the belly button. It begins with raised, red, hive-like patches (urticarial plaques) on the trunk, back, buttocks and limbs. Within 1 to 2 weeks, large tense blisters can form on the red plaques, and they may also appear on the palms and soles. The face, scalp and mucous membranes are usually not involved. The blisters contain clear fluid, occasionally blood-stained, and usually heal without scarring. DermNet gives the timing of blisters as 2 to 4 weeks, and says some people have no blisters but plaques of inflamed skin.

Other pregnancy rashes can look similar before blisters appear. The BAD has a separate leaflet on polymorphic eruption of pregnancy, and DermNet lists polymorphic eruption of pregnancy, pustular psoriasis of pregnancy and bullous pemphigoid among differential diagnoses.

The BAD says the appearance and behaviour of the rash are usually typical and easily diagnosed by a dermatologist, but before blisters appear it can resemble other skin diseases. A skin biopsy and a blood test for antibodies may be done to confirm it. DermNet says direct immunofluorescence on the biopsy shows linear C3 staining along the junction between the layers of skin in all cases, and blood tests can distinguish it from other autoimmune blistering disorders.

The BAD says it cannot be cured but can be controlled; the aims are relieving itch, preventing blisters and treating any secondary infection. Options it lists include steroid creams, dressings for weepy or raw areas, emollients, oral antihistamines suitable for pregnancy, and steroid tablets for blisters and itching, which may need to be increased at the end of pregnancy to prevent flare after delivery. For severe, persistent disease after delivery, immunosuppressant treatment or concentrated antibodies (IVIG) may be considered by the medical team. DermNet similarly describes topical steroids for mild disease and systemic corticosteroids for more extensive disease, using the lowest effective dose.

The BAD notes that oral steroids carry a risk of raised blood sugar and blood pressure, so blood pressure, urine tests and ultrasound scans are important, and that anyone on prolonged steroid treatment should not stop suddenly but follow their doctor's advice. These are specialist decisions: never start, stop or change a medicine without advice from your dermatologist or obstetric team. It is safe to breastfeed while taking steroid tablets, the BAD says, as only small amounts pass into breast milk.

The BAD adds a fire-safety note: emollients can catch fire when in contact with dressings, clothing, bedding or hair, so avoid smoking and naked flames near them and wash clothing and bed linen regularly.

The BAD says the baby is at increased risk of premature delivery and may be relatively small, so the pregnancy should be closely monitored by the obstetrician and midwives. DermNet says the risk correlates with the severity of the condition. In 5 to 10% of cases (the BAD figure; DermNet says about 10%) the baby develops a blistering rash after delivery from transfer of the mother's antibodies; it can last up to 6 weeks according to the BAD and usually improves with creams and emollients, though DermNet gives a clearance time of 3 to 4 months.

A caesarean is not routinely necessary for this condition unless there are other reasons, the BAD says, and blistering of the vulva and vagina occurs in 20% of affected women. Different sources give slightly different timings for the baby's rash; ask your paediatric team what to expect.

The BAD says symptoms usually resolve days or weeks after birth, but in some women the disease stays active for months and needs continued treatment. Restarting periods, oestrogen-containing oral contraceptives and further pregnancies can all trigger flare-ups. It may recur in later pregnancies, and DermNet notes onset may be earlier in subsequent pregnancies. The BAD points to the support group PEM Friends, and says some treatments in its leaflet may not be available on the NHS. Specialist dermatology and obstetric pathways differ between UK nations, so ask your team how your care will be shared.