Gestational Diabetes

Gestational diabetes is defined as carbohydrate intolerance of varying severity with onset or first recognition during pregnancy.^CEMACH Gestational diabetes mellitus (GDM) affects about 5% of all pregnancies and results in an increased incidence of Caesarean sections, perinatal traumas and neonatal complications.⁰⁵⁰² Controversy has surrounded its diagnosis, significance and treatment.

There is an increased risk of fetal macrosomia, early delivery and admission to the special care baby unit.⁰¹⁰¹

The World Health Organization has defined gestational diabetes mellitus and impaired glucose tolerance two hours after a 75 g oral glucose load as more than 11 mmol/l and 8-11 mmol/l respectively. However, these criteria were based on a nonpregnant population and because of the slowed response to a glucose load in pregnancy, particularly in the third trimester, this may lead to over diagnosis. Following an abnormal glucose tolerance test, many advocate dietary advice and further blood glucose monitoring before considering insulin treatment. The American Diabetes Association and the American College of Obstetricians and Gynecologists have endorsed the use of a 50 g oral glucose load at 24-28 weeks of gestation.

The significant threshold values for the 75-g oral glucose tolerance test (oGTT) during pregnancy have yet to be conclusively determined. Women undergoing a 75-g oGTT during the third trimester of pregnancy were classified into three groups: mild gestational impaired glucose tolerance (GIGT; 2-h postload glucose, 8.0-8.5 mmol/l; n=75), moderate-severe GIGT (8.6-10.9 mmol/l; n=167), and GDM (>/=11.0 mmol/l; n=76). Outcome indicators of these three groups of women were compared to the parameters of the women with a presumed normal carbohydrate metabolism (n=12,185). The results show that with increasing oGTT thresholds, there was an increasing risk of maternal morbidity in the form of hypertensive disorders complicating pregnancy, as well as obstetric intervention such as induction of labor, caesarean delivery, and preterm delivery. The infant was also at increasing risk with increasing oGTT thresholds from respiratory distress, macrosomia, and associated shoulder dystocia. It would appear, therefore, that abnormal glucose tolerance in pregnancy, even as defined by the World Health Organization criteria, has proportionate risks to both mother and child.⁰⁸⁰²

A glucose level of 7.8 mmol/l or more warrants a full diagnostic oral glucose tolerance test. Despite having the greatest sensitivity (79%) and specificity (87%) of the screening tests available, it is probably best reserved for high risk rather than general populations.

Screening using glycosylated haemoglobin or fructosamine have proved too insensitive for use in pregnancy. A national survey revealed widespread variation in the choice of screening methods in UK obstetric units.⁹⁹⁰¹ Figure 1 is a screening protocol for gestational diabetes.

(After Black RS and Gillmer MDG - TOG (2003) 5:143-148)

Women at risk of gestational diabetes include:

family history of Type 2 diabetes

previous gestational diabetes

previous unexplained stillbirth

glycosuria

polyhydramnios

large for dates baby

previous large for dates baby

obesity⁰⁵⁰²

age >34 years

some ethnic minorities⁹²⁰¹

 

The relative risk for gestational diabetes compared to White women, age < 25 years, BMI < 27, and parity < 3 was Black 3.1, South East Asian 7.6 , Indian 11.3.

Control of blood sugar is with reduced calorie diet and insulin if this proves inadequate. There has been some recent interest in the use of oral medication for gestational diabetes.⁰⁷⁰¹

Fat reduces insulin sensitivity, making avoidance of obesity in those with gestational diabetes especially important. GDM has a relationship with a history of PCOS, therefore in women with a history of PCOS, the risk of GDM should be considered.⁰⁸⁰¹

In those with gestational diabetes, following delivery, the sliding scale can be discontinued once the woman has started eating.

All those who have developed gestational diabetes requiring insulin should have a glucose tolerance test performed between six weeks and three months postpartum. It may be that an abnormal test in pregnancy has uncovered previously undiagnosed type 2 diabetes rather than just ‘gestational diabetes’. Even those with normal results at this time should be made aware of their lifetime risk of developing type 2 diabetes and advised to avoid excess weight gain and to take regular exercise.

Until recently, there was little supporting evidence that diagnosis and treatment of gestational diabetes produced any benefit. The study of Crowther et al⁰⁵⁰¹demonstrated that the rate of serious perinatal complications was significantly lower among the infants of the 490 women in the intervention group than among the infants of the 510 women in the routine-care group (1 percent vs. 4 percent; relative risk adjusted for maternal age, race or ethnic group, and parity, 0.33; P=0.01). However, more infants of women in the intervention group were admitted to the neonatal nursery (71 percent vs. 61 percent; adjusted relative risk, 1.13; P=0.01). Women in the intervention group had a higher rate of induction of labour than the women in the routine-care group (39 percent vs. 29 percent; adjusted relative risk, 1.36; P<0.001), although the rates of caesarean delivery were similar (31 percent and 32 percent, respectively; P=0.73). At three months post partum, data on the women's mood and quality of life, available for 573 women, revealed lower rates of depression and higher scores, consistent with improved health status, in the intervention group.

Sources: Black RS and Gillmer MDG - TOG (2003) 5:143-148

DISCLAIMER

The aim of this web site is to provide a general guide and it is not intended as a substitute for a consultation with an appropriate specialist in respect of individual care and treatment.