Twin pregnancies have been associated with adverse obstetric and neonatal outcomes. The incidence of respiratory distress syndrome in the newborns of multiple pregnancy patients is probably related to the higher incidence of preterm delivery. However, the complications of twin pregnancies are not limited to infants; miscarriages, preeclampsia, anemia, placenta previa, polyhydramnios, and premature rupture of membranes are more frequent than in singleton pregnancy. There have been a few reports that test the hypothesis that multiple gestation could also be a risk factor for gestational diabetes (16). These studies utilized various criteria for diagnosing gestational diabetes (World Health Organization [1], National Diabetes Data Group [24], and Carpenter and Coustan [7]) and did not report the percentage of the positive glucose challenge test for each group.

To determine the prevalence of gestational diabetes (using the Carpenter and Coustan criteria) in singleton and twin pregnancies in a cohort population of women who had had screening for gestational diabetes from January 1990 to January 2000, we started a retrospective study on 2,554 pregnant women screened for gestational diabetes in the Department of Obstetrics and Gynecology of our University Hospital. Of these, 70 were multiple pregnancies. A 50-g oral glucose challenge test was performed between 24 and 28 weeks’ gestation, and a 1-h value ≥135 mg/dl was considered positive and followed by a 100-g oral glucose tolerance test. The results were interpreted according to the Carpenter and Coustan threshold values (95, 180, 155, and 140 mg/dl) at fasting and after 1, 2, and 3 h, respectively. If two thresholds were met or exceeded, then the diagnosis of gestational diabetes was made. Age, familial or personal anamnestic factors, parity, and BMI at first visit, all considered risk factors for GDM, were recorded in our database. A positive glucose challenge test occurred in 520 of 2,554 pregnant women (20.3%). The test was positive in 22 of 70 (31.4%) multiple pregnancies and 498 of 2,484 (20.0%) singleton pregnancies (P = 0.029). The rates of GDM were 80 of 2,484 (3.6%) in singleton and 4 of 70 (5.7%) in twin pregnancies (P = 0.416). No statistically significant differences exist for the maternal risk factors for GDM between the two groups.

The decreased insulin sensitivity in pregnancy may be modified by several factors, such as diet, BMI, maternal age, and the placental mass, all of which may play a role affecting β-cell function and sensitivity to insulin. It has been suggested that in multiple pregnancies with two placentas or one that is larger, the incidence of gestational diabetes may be increased (3,4,6). Our data show that in our Sicilian population, twin pregnancy cannot be considered a proven risk factor for gestational diabetes. In fact, the differences (3.6 vs. 5.7%) are not statistically different. Our data showed that one-third of twin pregnancies (22 of 70, 31.4%) manifest a positive glucose challenge test, as compared with 20% of singleton pregnancies (498 of 2,484). It seems possible that with a larger sample size, the difference in incidence of gestational diabetes might have been statistically significant, although of questionable clinical significance. Another hypothesis could be that the greater relative elevation of anti-insulin placental hormone levels in a twin gestation may precipitate a mild degree of glucose intolerance in a woman who would have been normal with a singleton pregnancy. If this were the case, the impact of such a mild degree of glucose intolerance remains undetermined.

The authors thank Prof. D.R. Coustan (Brown University, Providence, RI) for critical reading of the manuscript.

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Address correspondence to F. Corrado, MD, Department of Obstetrics and Gynecology, Policlinico Universitario “G. Martino” 98100, Messina, Italy. E-mail: francesco.corrado@unime.it.