TORONTO — Women who diet to lose weight before getting pregnant could be at increased risk of giving birth prematurely, according to Jim Johnstone of the department of physiology at the University of Toronto.
The findings, which he presented at the annual meeting of the Society for Gynecologic Investigation, come from a subset of the Southampton Women's Survey, in which 12,500 women aged 24–34 years were interviewed before they became pregnant, and then 3,000 were followed through their subsequent pregnancies.
In Mr. Johnstone's sample of 605 of these pregnant women, 23.3% had indicated before conception that they were dieting to lose weight. However, the time interval between the survey interview and their subsequent pregnancy was not recorded.
The analysis revealed that women who became pregnant after a weight-loss diet were significantly more likely to give birth prematurely, compared with women who did not diet (11% vs. 5%). This finding was independent of maternal body mass index, smoking status, exercise, socioeconomic status, ethnicity, and infant gender.
In addition, a total of 50 placental samples selected randomly from the group at term showed that—compared with nondieters—dieters had decreased levels of the enzyme 11β hydroxysteroid dehydrogenase type 2 (11β HSD2), indicating increased fetal exposure to cortisol, as well as increased levels of cyclooxygenase-2 (COX-2), indicating an increased placental capacity to produce prostaglandins.