The women had not had diabetes or other chronic illnesses before becoming pregnant. The authors also found that when two servings per week of potatoes were dropped in favor of other vegetables, legumes, or whole grain foods, women had a nine to 12 percent lower risk of developing diabetes during pregnancy. However, until the current study, the effect of potatoes, a common, high-glycemic food, on the development of gestational diabetes was unknown. Previous studies have found that a diet with a higher glycemic index is related to higher plasma glucose and HbA1c concentrations during pregnancy14 15 and could increase the risk of GDM.16 The association between consumption of potatoes, a commonly consumed food with a high glycemic index, and GDM risk, remains unknown. Results During the 10 years of follow-up, we documented 854 incident pregnancies affected by GDM among 21 693 eligible singleton pregnancies from 15 632 women (6061 women with more than one pregnancy). They estimated reductions in gestational diabetes risk by substituting the following foods for two servings of potatoes per week: 
 
 9 percent for other vegetables 
 
 10 percent for legumes 
 
 12 percent for whole grain foods 
 
 The authors cautioned, however, that because their study was not designed to prove cause and effect, their results do not prove conclusively that potato consumption directly leads to gestational diabetes. Table 2 Relative risks (95% confidence intervals) for gestational diabetes mellitus according to total potato consumption before pregnancy View this table: Fig 1 Risk of gestational diabetes mellitus (GDM) associated with substitution of all vegetables (not including potatoes), legumes, or whole grain foods for potatoes at same serving amount (two servings/week). Discussion In this large prospective cohort study, we found that higher pre-pregnancy consumption of potatoes was significantly associated with a greater risk of gestational diabetes mellitus (GDM), even after adjustment for other major risk factors for GDM such as age, family history of diabetes, physical activity, overall diet quality, and BMI. The researchers propose that substituting potatoes with other vegetables, legumes or whole grains may help lower gestational diabetes risk. "However, as the researchers acknowledge, these results need to be investigated in a controlled trial setting before we can know more. "We found that a diet with a higher level of potato consumption before pregnancy was related to a greater risk of developing diabetes during pregnancy," said study author Dr. Cuilin Zhang, senior investigator in the Epidemiology Branch of the Division of Intramural Population Health Research at NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development.
– If your short-term plan involves getting pregnant, your immediate plan should potentially be to lay off the potatoes. So suggests a National Institutes of Health study published Tuesday in the BMJ that found women who eat more potatoes before becoming pregnant may be more likely to develop gestational diabetes as compared to their spud-light counterparts. That finding stems from an analysis of 15,632 women who participated in the Nurses' Health Study II over a 10-year period beginning in 1991. A press release explains the women had not previously had gestational diabetes, and at four-year intervals answered questions related to their diet in the year prior. Under the potato category, they were asked to rate their consumption of baked, boiled, or mashed potatoes, fries, or potato chips on a scale of "never" to "six or more times a day." The researchers begin their study by noting just how prevalent potato consumption is, with 35% of American women ages 19-50 eating potatoes daily, and the vegetable accounting for 8% of their caloric intake. Study author Dr. Cuilin Zhang recommends to CBS News that women cap it at one potato portion per week and consider a swap. The researchers estimate that trading two servings of potatoes weekly for a substitute vegetable, legumes, or whole-grain food would reduce the risk of gestational diabetes—which CBS reports affects as many as 8% of pregnancies—by 9% to 12%. As for why women should care, Zhang tells the BBC that women with gestational diabetes can develop pre-eclampsia and hypertension, which "can adversely affect the fetus" and put the mother at higher risk of developing Type 2 diabetes. The team notes, however, that the study shows correlation, not causation, and says more research is needed. (One country has told its women not to get pregnant right now.)