INCREASED MATERNAL FASTING PROINSULIN AS A PREDICTOR OF INSULIN REQUIREMENT IN WOMEN WITH GESTATIONAL DIABETES

Circulating proinsulin was assessed during a 75g OGTT in 55 pregnant w omen who fulfilled WHO criteria for impaired glucose tolerance before the 32nd gestational week. Proinsulin was assayed retrospectively usin g a two-site immunoradiometric assay and immunoreactive insulin by rad ioimmunoassay. Of the 55 women, 19 required insulin treatment in addit ion to diet later in pregnancy. Fasting proinsulin concentrations were significantly higher in the 19 women who later required insulin treat ment compared with the 36 women treated with diet alone (3.4 +/- 0.7 v s 1.8 +/- 0.2 pmol l-1, p < 0.005). There was no difference between th e treatment groups of 60 and 120 min proinsulin values during the OGTT . Fasting plasma glucose and immunoreactive insulin were similar in th e insulin-treated and diet-treated women and remained similar during t he OGTT. No women within the insulin-treated group had a fasting plasm a proinsulin value < 1.1 pmol l-1 in contrast with 12 women in the die t-treated group (p = 0.01 23). Ten of the 19 insulin-treated women had a fasting plasma proinsulin > 2.5 pmol l-1 compared with 8 of the 36 diet-treated women (p = 0.0346). Fasting proinsulin values early in pr egnancy have prognostic implications in women with gestational diabete s.