levels in blood samples without challenging the subject with glucose solutions. a blood glucose level is determined when fasting, two hours after a meal, or simply at any random time. in contrast, challenge tests involve drinking a glucose solution and measuring glucose concentration thereafter in the blood; in diabetes, they tend to remain high. the glucose solution has a very sweet taste which some women find unpleasant; sometimes, therefore, artificial flavours are added. some women may experience nausea during the test, and more so with higher glucose levels. there is currently not enough research to show which way is best at diagnosing gestational diabetes. routine screening of women with a glucose challenge test may find more women with gestational diabetes than only screening women with risk factors. hemoglobin a1c (hba1c) is not recommended for diagnosing gestational diabetes, as it's a less reliable marker of glycemia during pregnancy than oral glucose tolerance testing (ogtt). pathways opinions differ about optimal screening and diagnostic measures, in part due to differences in population risks, cost-effectiveness considerations, and lack of an evidence base to support large national screening programs. the most elaborate regimen entails a random blood glucose test during a booking visit, a screening glucose challenge test around 24–28 weeks' gestation, followed by an ogtt if the tests are outside normal limits. if there is a high suspicion, a woman may be tested earlier. in the united states, most obstetricians prefer universal screening with a screening glucose challenge test. in the united kingdom, obstetric units often rely on risk factors and a random blood glucose test. the american diabetes association and the society of obstetricians and gynaecologists of canada recommend routine screening unless the woman is low risk (this means the woman must be younger than 25 years and have a body mass index less than 27, with no personal, ethnic or family risk factors) the canadian diabetes association and the american college of obstetricians and gynecologists recommend universal screening. the u.s. preventive services task force found there is insufficient evidence to recommend for or against routine screening, and a 2017 a cochrane review found that there is not evidence to determine which screening method is best for women and their babies. some pregnant women and careproviders choose to forgo routine screening due to the absence of risk factors, however this is not advised due to the large proportion of women who develop gestational diabetes despite having no risk factors present and the dangers to the mother and baby if gestational diabetes remains untreated. non-challenge blood glucose tests when a plasma glucose level is found to be higher than 126 mg/dl (7.0 mmol/l) after fasting, or over 200 mg/dl (11.1 mmol/l) on any occasion, and if this is confirmed on a subsequent day, the diagnosis of gdm is made, and no further testing is required. these tests are typically performed at the first antenatal visit. they are simple to administer and inexpensive, but have a lower test performance compared to the other tests, with moderate sensitivity, low specificity and high false positive rates. screening glucose challenge test the screening glucose challenge test (sometimes called the o'sullivan test) is performed between 24 and 28 weeks, and can be seen as a simplified version of the oral glucose tolerance test (ogtt). no previous fasting is required for this screening test, in contrast to the ogtt. the o'sullivan test involves drinking a solution containing 50 grams of glucose, and measuring blood levels one hour later. if the cut-off point is set at 140 mg/dl (7.8 mmol/l), 80% of women with gdm will be detected. if this threshold for further testing is lowered to 130 mg/dl, 90% of gdm cases will be detected, but there will also be more women who will be subjected to a consequent ogtt unnecessarily. oral glucose tolerance test a standardized oral glucose tolerance test (ogtt) should be done in the morning after an overnight fast of between 8 and 14 hours. during the three previous days the subject must have an unrestricted diet (containing at least 150 g carbohydrate per day) and unlimited physical activity. the subject should remain seated during the test and should not smoke throughout the test. iadpsg (international association of diabetes and pregnancy study groups) has developed diagnostic criteria for gdm, based on the results of adverse pregnancy outcomes in the hyperglycemia and adverse pregnancy outcomes (hapo) study. these were recommended by who 2013. according to these gestational diabetes mellitus should be diagnosed at any time in pregnancy if one of the following criteria are met, using a 75 g glucose ogtt: fasting blood glucose level ≥92 mg/dl (5.1 mmol/l) 1 hour blood glucose level ≥180 mg/dl (10 mmol/l) 2 hour blood glucose level ≥153 mg/dl (8.5 mmol/l) urinary glucose testing women with gdm may have high glucose levels in their urine (glucosuria). although dipstick testing is widely practiced, it performs poorly, and discontinuing routine dipstick testing has not been shown to cause underdiagnosis where universal screening is performed. increased glomerular filtration rates during pregnancy contribute to some 50% of women having glucose in their urine on dipstick tests at some point during their pregnancy. the sensitivity of glucosuria for gdm in the first two trimesters is only around 10% and the positive predictive value is around 20%. prevention vitamin d supplementation during pregnancy may help to prevent gestational diabetes. a 2015 review found that when done during pregnancy moderate physical exercise is effective for the prevention of gestational diabetes. a 2014 review however did not find a significant effect. it is uncertain if additional dietary advice interventions help to reduce the risk of gestational diabetes. however, data from the nurses' health study shows that adherence to a healthy plant-based diet is associated with lower risk for gdm. diet and physical activity interventions designed to prevent excessive gestational weight gain reduce the rates of gestational diabetes. however, the impact of these interventions varies with the body-mass index of the person as well as with the region in which the studies were performed. moderate-quality evidence suggest that there is a reduced risk of gestational diabetes mellitus and caesarean section with combined diet and exercise interventions during pregnancy as well as reductions in gestational weight gain, compared with standard care. a 2023 review found that a plant-based diet (including fruits, vegetables, whole grains, nuts and seeds, and tea) rich in phytochemicals lowers the risk of gdm. it has been suggested that for women who have had gestational diabetes, diet, exercise, education, and lifestyle changes between pregnancies may lower their chances of having gestational diabetes again in future pregnancies. however, there is no research to show whether interventions between pregnancies lower the number of women who develop gestational diabetes again. management main article: diabetes management a kit with a glucose meter and diary used by a woman with gestational diabetes treatment of gdm with diet and insulin reduces health problems mother and child. treatment of gdm is also accompanied by more inductions of labour. a repeat ogtt should be carried out 6 weeks after delivery, to confirm the diabetes has disappeared. afterwards, regular screening for type 2 diabetes is advised. lifestyle interventions include exercise, diet advice, behavioural interventions, relaxation, self-monitoring glucose, and combined interventions. women with gestational diabetes who receive lifestyle interventions seem to have less postpartum depression, and were more likely to reach their weight loss targets after giving birth, than women who had no intervention. their babies are also less likely to be large for their gestational age, and have less percentage of fat when they are born. more research is needed to find out which lifestyle interventions are best. some women with gdm use probiotics but it is very uncertain if there are any benefits in terms of blood glucose levels, high blood pressure disorders or induction of labour. if a diabetic diet or g.i. diet, exercise, and oral medication are inadequate to control glucose levels, insulin therapy may become necessary. the development of macrosomia can be evaluated during pregnancy by using sonography. women who use insulin, with a history of stillbirth, or with hypertension are managed like women with overt diabetes. lifestyle counselling before pregnancy (for example, about preventive folic acid supplements) and multidisciplinary management are important for good pregnancy outcomes. most women can manage their gdm with dietary changes and exercise. self monitoring of blood glucose levels can guide therapy. some women will need antidiabetic drugs, most commonly insulin therapy. any diet needs to provide sufficient calories for pregnancy, typically 2,000–2,500 kcal with the exclusion of simple carbohydrates. the main goal of dietary modifications is to avoid peaks in blood sugar levels. this can be done by spreading carbohydrate intake over meals and snacks throughout the day, and using slow-release carbohydrate sources—known as the g.i. diet. since insulin resistance is highest in mornings, breakfast carbohydrates need to be restricted more. the mediterranean diet may be associated with reduced incidence of gestational diabetes. however, there is not enough evidence to indicate if one type of dietary advice is better than another. regular moderately intense physical exercise is advised, although there is no consensus on the specific structure of exercise programs for gdm. pregnant women who exercise have lower blood sugar levels when fasting and after meals compared to those who do not exercise. it is not clear which form of exercise is best when pregnant. self monitoring can be accomplished using a handheld capillary glucose dosage system. compliance with these glucometer systems can be low. there is not a lot of research into what target blood sugar levels should be for women with gestational diabetes and targets recommended to women vary around the world. target ranges advised by the australasian diabetes in pregnancy society are as follows: fasting capillary blood glucose levels <5.5 mmol/l 1 hour postprandial capillary blood glucose levels <8.0 mmol/l 2 hour postprandial blood glucose levels <6.7 mmol/l regular blood samples can be used to determine hba1c levels, which give an idea of glucose control over a longer time period. research suggests a possible benefit of breastfeeding to reduce the risk of diabetes and related risks for both mother and child. medication if monitoring reveals failing control of glucose levels with these measures, or if there is evidence of complications like excessive fetal growth, treatment with insulin might be necessary. this is most commonly fast-acting insulin given just before eating to blunt glucose rises after meals. care needs to be taken to avoid low blood sugar levels due to excessive insulin. insulin therapy can be normal or very tight; more injections can result in better control but requires more effort, and there is no consensus that it has large benefits. a 2016 cochrane review concluded that quality evidence is not yet available to determine the best blood sugar range for improving health for pregnant women with gdm and their babies. there is some evidence that certain medications by mouth might be safe in pregnancy, or at least, are less dangerous to the developing fetus than poorly controlled diabetes. when comparing which diabetes tablets (medication by mouth) work best and are safest, there is not enough quality research to support one medication over another. the medication metformin is better than glyburide. if blood glucose cannot be adequately controlled with a single agent, the combination of metformin and insulin may be better than insulin alone. another review found good short term safety for both the mother and baby with metformin but unclear long term safety. people may prefer metformin by mouth to insulin injections. treatment of polycystic ovarian syndrome with metformin during pregnancy has been noted to decrease gdm levels. almost half of the women did not reach sufficient control with metformin alone and needed supplemental therapy with insulin; compared to those treated with insulin alone, they required less insulin, and they gained less weight. with no long-term studies into children of women treated with the drug, there remains a possibility of long-term complications from metformin therapy. babies born to women treated with metformin have been found to develop less visceral fat, making them less prone to insulin resistance in later life. prognosis gestational diabetes generally resolves once the baby is born. based on different studies, the chances of developing gdm in a second pregnancy, if a woman had gdm in her first pregnancy, are