"The number of patients with psoriasis who improve in pregnancy is double the number of patients who worsen in pregnancy," Jenny E. Murase, MD, and colleagues write in the May issue of Archives of Dermatology.
The researchers say hormonal changes during pregnancy may play a role in improving psoriasis.
"It was previously suggested that progesterone was most likely responsible for this improvement," they write. "However, our findings indicate that increased estrogen levels, and especially increased levels of estrogen relative to progesterone, correlate with psoriatic improvement."
The researchers compared changes in psoriasis in a group of 47 pregnant women and 27 nonpregnant women of childbearing age. After receiving instructions, the women measured the area of their psoriasis, marked areas of psoriasis on a diagram, and rated the severity of their psoriasis five times over the course of a year.
Blood hormone levels for progesterone and estrogen were measured.
Pregnancy Improves Psoriasis
During pregnancy, 55% reported an improvement, 21% reported no change, and 23% reported a worsening in psoriasis.
The measured areas of psoriasis decreased during pregnancy, with a significant drop between the 10th and 20th weeks of pregnancy.
In the group of nonpregnant women, levels of psoriatic body surface area remained the same throughout the year.
Psoriasis Relief Fades Postpartum
Six weeks after giving birth, 65% of the patients reported a worsening of their psoriasis, while 26% reported no change and only 9% reported improvement.
On average, the area of psoriasis doubled between the 30th week of pregnancy and six weeks after delivery. But the researchers note that the patients' psoriasis did not become any worse during the postpartum period than it had been during the first trimester.
When the study group returned to prepregnancy hormone levels, there was no difference between the amounts of body area with psoriasis in the two groups.
"In other words," the researchers write, "the 'postpartum flare' previously described by patients anecdotally was really a return to the patients' baseline."
Strong Link to Hormone Levels
The researchers tracked hormone levels during and after pregnancy and found that fluctuations in psoriasis areas corresponded with changes in levels. There was no link between psoriasis and progesterone levels.
"We believe that further examination of how estrogen may improve psoriasis is warranted," the researchers write. "Whether estriol [an estrogen found during pregnancy] can improve psoriasis or can prevent worsening of psoriasis in menopause should be explored."
The study was funded in part by grants from the National Institutes of Health, the National Center for Research Resources, and the National Psoriasis Foundation.