Introduction

Gestational diabetes is a condition characterized by high blood glucose levels that is first recognized during pregnancy. The condition occurs in approximately 4% of all pregnancies. Pregnancy is a state of insulin resistance, relative glucose intolerance, and maternal hyperinsulinemia. The insulin resistance likely results from placental production of anti-insulin hormones such as human chorionic somatotropin (hCS) (also known as human placental lactogen), cortisol, and glucagon. Fasting glucose levels are reduced in pregnancy while postprandial glucose levels are elevated in comparison with the nonpregnant state. Insulin production is increased twofold in normal pregnant women. In diabetic women insulin requirement also rise. High risk women should be screened for gestational diabetes as early as possible during their pregnancies. All women should be screened between the 24th and 28th week of pregnancy. When maternal diabetes precedes the pregnancy it is associated with an increased risk of miscarriage, congenital abnormalities, accelerated fetal growth, late stillbirth, birth trauma, neonatal hypoglycaemia and long-term health problems for the child. Gestational diabetes is associated with those complications attributable to maternal hyperglycaemia arising in the later half of pregnancy.

There is still controversy concerning optimal strategy for detection and diagnosis of gestational diabetes mellitus. For screening and diagnosis of diabetes in selective population the American Diabetes Association (ADA) recommends two step procedure. It has been found that universal screening for GDM detects more cases as compared with selective screening, so will improve maternal and fetal prognosis. Compared to Caucasian women, Indian women have eleven fold increased risk of developing glucose intolerance during pregnancy. For this we need a universal screening procedure which is economical as well as feasible. Thus we conducted a study to find out one step procedure which could serve both diagnostic and screening tool and which is economical, feasible and acceptable.

METHOD

This study was carried out in the Dept of Obstetrics and Gynecology at Teerthankar Mahaveer Medical College and Research Centre, Moradabad, U.P. from Feb 2010 to Dec 2011. In this study 800 pregnant women in 2^nd or 3^rd trimester attending antenatal clinic were selected for oral glucose challenge test .Each one of them were given 50 g oral glucose load for glucose challenge test (GCT) and the venous blood samples were collected after 1 hour . They were all advised to come after 72 hours on an empty stomach for the 75 g oral glucose tolerance test (OGTT) recommended by WHO .

Blood pressure measurement and the body mass index were recorded. Family history of diabetes, history of previous pregnancies, and the socio-economic status also noted .Out of 800 pregnant women only 540 were reported for 75 g oral glucose tolerance test (OGTT).  A fasting venous blood sample was collected and they were given 75 g oral glucose and again after 2 hours the venous blood was again collected. The plasma glucose was estimated by glucose oxidation and per-oxidation (GOD-POD) method by using Erba kit.

The comparative analysis of the results was done taking into consideration the screening procedure recommended by American Diabetes Association (ADA) (Table 1) and WHO (Table 2)

Table 1: Diagnosis of GDM.

For a positive diagnosis of GDM two or more than two values of the venous concentrations must exceed the above values.

According to WHO criteria for diagnosis of GDM after 2 hour 75 gm OGTT the threshold plasma glucose concentration must be more than 140 mg/dl in comparison to that of impaired glucose tolerance (IGT) in non-pregnant women.

Table 2: WHO criteria.

A pregnant woman is classified as a case of GDM if she fulfills the WHO criteria for impaired glucose tolerance (IGT) or is diabetic with 75 gm glucose challenge. A case is diagnosed as a case of IGT if she presents with a fasting plasma glucose value of <126 mg/dl and 2 hour post plasma glucose is >140 mg/dl and <200 mg/dl. Two hour post plasma glucose values are more important in making diagnosis of IGT as compared to fasting plasma glucose value.

Discussion

Increased blood sugar levels in pregnancy increases morbidity in mothers. It also increases the chances of subsequent diabetes. Increased hyperglycemia in mother also has a direct impact on fetal pancreas which makes infant susceptible for diabetes in future and this effect is independent of genetic factors. Different surveys suggested that prevalence of IGT is more in the reproductive age group women in their fourth decade as compared to prevalence in their third decade. Also there is continuous increasing trend of gestational diabetes in Indian women and these women are more responsible for maternal and fetal morbidity. So it has become important to screen these women and to decrease the incidence of maternal and fetal morbidity. In India universal screening is recommended over selective screening as recommended by American Diabetic Association (ADA).

Fasting Plasma Glucose (FPG) as a screening procedure

Sacks et al and Daniele et al proposed a cut off value of 95 mg/dl for screening of GDM and they observed that easier screening procedure for GDM is measurement of FBG. But later on it was observed that measurement of FBG is not a sufficient marker for screening of GDM because in most of the cases the FBG values are below the threshold values and very few cases were diagnosed as a case of GDM by the sole estimation of FBG. In cases where FBG is increased but the values for 2 hour plasma glucose is within normal limits then there is suspicion about fasting state of the subject. We would have diagnosed a higher number of pregnant women with GDM if FPG alone is used as a screening method. In our study we observed that 31% of pregnant women had FPG ≥ 95 mg%. For this reason the diagnosis of GDM by fasting plasma glucose is not recommended by WHO.

50 gm GCT

In this study we screened 800 pregnant women by glucose challenge test with 50 gm of glucose . Out of 800 pregnant women 260 did not turn up for 75 gm OGTT. It was reported by Magee et al that 91 out of 457 positive screen individual failed to undergo diagnostic test in their follow up. Similar observations were also noticed by de Aguiar et al. In their study they observed that 23% of their screen positive women did not turn up for OGTT. This non compliance occurred in our country because it is difficult to make women come for blood test repeatedly and also the requirement of number of blood samples is not feasible and conclusive. The most important observation in this study was identification of 21 (22.83%) potential GDM women who were negative as per GCT criteria. Usually OGTT is performed only for GCT positive but in our study we performed both tests in same women.

GCT with 50 gm glucose of FBG estimation needs confirmation by OGTT and thus can`t be used as one step procedure for screening as well as diagnosis of GDM which we are looking for.

Presently the ADA criteria are not used commonly because these criteria were originally validated against the risks associated with maternal diabetes and not based on the chances of development of adverse perinatal outcome. Pettitt favored WHO criteria. In day to day practice 2 hour glucose level is preferred for diagnosis of GDM.

Table 3: Glucose challenge test (GCT) and oral glucose tolerance test (OGTT).

As shown in Table 3 according to WHO criteria 92 women (17.03%) were diagnosed as a case of GDM. Out of these 92 GDM women 71 (77.17%) women were GCT positive and 21 (22.83 %) were GCT negative. In our study we analyzed the values taking into consideration the ADA and WHO criteria for diagnosis of GDM. Among 540 pregnant women  167 (30.92%) had FPG ≥ 95 mg/dl, 42 (7.27%) had 2 hr PPG ≥ 155 mg/dl and 92 (17.03%) had 2 hr PPG ≥ 140 mg/dl. Twenty two (4.07%) of them had both FPG    ≥ 95 mg/dl, and 2 hr PPG ≥ 155 mg/dl as per ADA diagnostic criteria of GDM whereas by WHO criteria of 2 hr PPG ≥ 140 mg/dl 92 (17.03%) were identified as GDM.

In present study by ADA criteria of FBG ≥ 95 mg and 2 hour post prandial glucose ≥ 155 mg the prevalence of GDM was 22(4.07%) whereas the prevalence was 92 (17.03%) by WHO criteria. In Schmidt et al study the prevalence was 2.4% by ADA and 7.2% by WHO criteria. In Schmidt et al study the diagnostic pick up rate was three times more with WHO criteria as compared with ADA criteria. In our study diagnostic pick up rate was four times more with WHO criteria than with ADA criteria. This can be explained as Indian women are more prone to develop GDM. With WHO testing criteria for GDM more women were detected with adverse outcome than the ADA test.GDM detected by any of the screening test predicts adverse pregnancy outcome , so it is further important to detect GDM as early as possible to start treatment and improve pregnancy outcome. It has been found that WHO criteria of 2 hr PPG ≥ 140 mg/dl can detect large no of cases and has a great potential in it`s prevention as confirmed by Meltzer et al. The main drawback with ADA criteria is that it permits both 100 gm and 75 gm OGTT with same cut off value even though the load is different. The 3 hr value for 75 gm OGTT is not given (Table I).

All the factors, discussions and published evidences clearly establishes WHO criteria over ADA criteria as one step screening method.

The relative risk of developing GDM in Indian women is much more in comparison with white women. Also Indian women have high prevalence of diabetes. The high prevalence risk necessitates universal screening for glucose intolerance during pregnancy. GDM diagnosis is overlooked in about 1/3^rd of women where selective rather than universal screening is performed thus missing a vast majority of women likely to have glucose intolerance.

For universal screening we suggest a single GCT with a 75 gm of oral glucose load and diagnosing women with 2 hr PPG ≥ 140 mg/dl as GDM. This method suggested by WHO serves both as one step screening  and diagnostic procedure and is easy to perform as well as economical with better patient compliance as number of visits and number of needle pricks are very much less.

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