5








Glycaemic control and its measurement

 
     
 

KEY FINDINGS

  • Only 37% of women with diabetes had a measurement of glucose control recorded in the 6 months prior to pregnancy.
  • Women with type 2 diabetes and those from an ethnic minority were those most likely not to have had a documented glycaemic test by the end of the first trimester.
  • Only 38% of women with a HbA1c measured by 13 weeks of gestation had a value of less than 7%.
 
 
 

5.1

 

Introduction

It is accepted that good glycaemic control should be achieved prior to and during pregnancy, in order to reduce the risk of adverse outcomes. Elevated blood glucose levels in the periconception period are associated with higher rates of miscarriage and major congenital malformations.1–3 The purpose of this chapter is to provide a description of the tests used to measure glycaemic control, their use in the planning and management of glycaemic control in pregnancy and an overview of levels of glycaemic control achieved at the different stages of pregnancy. Measurements of HbA1c tests, or their equivalent, corresponding to the 6 months prior to pregnancy and to three points during the antenatal period (closest to 10 weeks, 20 weeks and 34 weeks of gestation), were requested as part of the data collection. For each measurement provided, the specified laboratory range for good control at the maternity unit was also requested.

 
 

5.2

 

Type of test used and recommended reference range

HbA1c should be used to monitor long-term glycaemic control, as it is the only measure for which good data are available on the risk of subsequent diabetic complications.4 The vast majority of measurements in England, Wales and Northern Ireland were based on the HbA1c test (Table 5.1). However, there were a few other types of test in use.

The data collection did not determine whether individual HbA1c values were Diabetes Control and Complications Trial (DCCT) aligned. However, the majority of units in England, Wales and Northern Ireland (741) reported using a DCCT-aligned assay in 2002.

The specified local laboratory reference ranges for good control were variable, with 14.8% of tests having a reference range of less than 6%, 62.8% between 6.0% and 6.9%, 19.8% between 7.0% and 7.9% and 2.5% having a reference range of 8% or more. This may reflect some laboratories quoting a non-diabetic reference range (typically around 4.5–6.0%) with others possibly quoting a target range for good control in diabetes (usually 6.5–7.5%).

 
 

5.3

 

Glycaemic control tests

Only 1414 (37.1%) of all the women had a measurement of glucose control documented in the 6 months prior to pregnancy (Table 5.1). This implies that a significant proportion of women are entering pregnancy with little or no preparation. The proportion of reported tests rose to 71.7% by the end of the first trimester. These figures are dependent upon information being documented in the medical records and may therefore be an underestimate.

The maternal characteristics associated with having had a glycaemic test prior to pregnancy and by 13 weeks of gestation are described in Table 5.2. Women with type 2 diabetes were less likely than women with type 1 diabetes to have had a documented prepregnancy test of glycaemic control (P < 0.001) (Table 5.2). They were also less likely to have had a test by 13 weeks in pregnancy (P < 0.001) (Table 5.2). This suggests that prepregnancy and early preparation for this group is less critically managed or these women are not accessing services.

Women from Black, Asian and Other ethnic minority groups were also significantly less likely to have had a documented prepregnancy test of glycaemic control (P < 0.001) (Table 5.2). This difference was also apparent in early pregnancy. This suggests social and cultural differences that need further evaluation.

Women aged 20–24 years at delivery were the least likely to have had a documented prepregnancy test of glycaemic control. However, women above 35 years of age were the least likely to have had a documented test of glycaemic control by 13 weeks. This aspect needs further investigation, as these women are more likely by age alone to be at risk of chromosomal abnormalities, which makes their apparent lack of prepregnancy preparation more surprising.

 
 

5.4

 

Glycaemic control values

During the preconception period and throughout pregnancy it is recommended that tests of long-term glycaemic control should be within the normal non-diabetic range; that is, HbA1c below 7%.5 The values reported in this section are based on the women who had HbA1c measurements recorded (see Table 5.1). If more than one value was provided within a given time period then the one which was taken at a gestation closest to the defined time period was included and the other values excluded. Values were also excluded if the timing of the test was outside the specified gestational range.

The median values of HbA1c recorded prepregnancy and at subsequent stages during the pregnancy, according to the type of diabetes, are described in Table 5.3. The proportion of women with values of HbA1c less than 7% at these different stages of pregnancy is also shown in Table 5.3.

The median value of HbA1c prepregnancy for women with diabetes was 7.9%. The greatest reduction in HbA1c values was seen by 20 weeks of gestation for women with either type 1 or type 2 diabetes.

Women with type 1 diabetes had higher values of HbA1c throughout the various stages than those with type 2. Only 65.7% of women with type 1 diabetes achieved HbA1c values below 7% by mid-pregnancy compared with 80.5% of women with type 2 diabetes (Table 5.3).

The median values of HbA1c, before pregnancy and at subsequent stages during the pregnancy, according to the outcome of the pregnancy, are described in Table 5.4. The proportion of women with values of HbA1c less than 7% at these different stages of pregnancy, according to the pregnancy outcome, is also shown in Table 5.4.

Higher prepregnancy HbA1c values were observed in women who had a baby with a major congenital malformation and in those women who had a normally formed stillbirth or neonatal death. Both these groups of women had poorer glycaemic control throughout the pregnancy compared with women who had a normal baby. The poorest control was seen in those women who had a normally formed stillbirth or neonatal death, with less than half of this group achieving HbA1c values of less than 7% at any stage in pregnancy. These observations support the aim of good glycaemic control periconceptionally and throughout pregnancy.

Good control as measured by HbA1c is not, in itself, predictive of a good outcome. One-quarter of the women who had a baby with a congenital malformation had an HbA1c value of less than 7% by 13 weeks of gestation. The value of HbA1c is acting as a surrogate marker for glycaemic control and may not reflect fluctuations of glucose levels. Further research in this area is warranted.

 
 

5.5

 

Discussion

 
 

5.5.1

 

Tests

Only 37% of women with diabetes had a measurement of glucose control recorded in the 6 months prior to pregnancy. Although this figure is likely to be an underestimate, as it was dependent upon the quality of medical records, such a low figure clearly needs further review.

Women with type 2 diabetes and those from a Black, Asian or Other ethnic minority were those most likely not to have had a glycaemic test before pregnancy and by the end of the first trimester and the reasons for this require exploration. These findings are of particular concern in light of the increasing prevalence of type 2 diabetes in the young adult population.6

 
 

5.5.2

 

Glycaemic control

All groups of women with diabetes, regardless of type or ethnic group, should be entering pregnancy with substantially better glycaemic control than observed in this study. Only 38% of women with an HbA1c value available by 13 weeks of gestation had a value of less than 7%. This does not compare well with other European countries, such as The Netherlands, where 75% of women with type 1 diabetes achieved HbA1c of 7% or less in the first trimester.7 This suggests that considerable improvements in periconceptional glycaemic control can be achieved in the UK population.

The reduction in glycaemic values observed by around 20 weeks of gestation is, in part, physiological, as there is a reduction in levels due to the increased haematopoiesis and the presence of new unglycated red cells in the circulation in pregnancy.8 Health professionals and women may frequently be unaware of this pattern and may attribute this physiological shift to an improvement in control.

The relationship between poor periconceptional glycaemic control and poor perinatal outcome observed is consistent with other studies. Poor control during pregnancy was particularly notable in the women with normally formed stillbirths or neonatal deaths. These observations continue to support the policy of aiming to maintain the HbA1c value at less than 7% before pregnancy and throughout pregnancy.

HbA1c is a measurement of ‘average’ control of glucose over a period of time and does not measure the extent and frequency of fluctuations from normal glycaemia. Further research is needed in this area, to identify other aspects of control that may give further insight into how to further reduce adverse perinatal outcomes.

 
 

5.6

 

Conclusion

Nearly 15 years on from the St Vincent Declaration in 1989, babies born to women with diabetes in England, Wales and Northern Ireland continue to have high perinatal mortality rates and congenital anomaly rates (see Chapter 7). The importance of periconceptional glycaemic control was known by the 1980s and has been reinforced by randomised control evidence in 1996.9 Despite this, only a minority of women in this study achieved good glycaemic control by the end of the first trimester.

More work is required to elucidate how women with diabetes can commence pregnancy with improved glycaemic control.

 
     

References

  1. Miller E, Hare JW, Cloherty JP, Dunn PJ, Gleason RE, Soeldner JS, et al. Elevated maternal haemoglobin A1c in early pregnancy and major congenital anomalies in infants of diabetic mothers. N Engl J Med 1981;304:1331–4.
  2. Karlsson K, Kjellmer I. The outcome of diabetic pregnancies in relation to the mother's blood sugar level. Am J Obstet Gynecol 1972;213–20.
  3. Kitzmiller J, Buchanan T, Kjos S, Combs C, Ratner R. Pre-conception care of diabetes, congenital malformations, and spontaneous abortions. Diabetes Care 1996;19:514–41.
  4. Marshall SM, Barth JH. Standardization of HbA1c measurements: a consensus statement. Diabetic Med 2000;17:5–6.
  5. Department of Health. National Service Framework for Diabetes (England) Standards. London: The Stationery Office; 2001 [www.dh.gov.uk/PublicationsAndStatistics/Publications/PublicationsPolicyAndGuidance/PublicationsPolicyAndGuidanceArticle/fs/en?CONTENT_ID=4002951&chk=09Kkz1].
  6. Hotu S, Carter B, Watson PD, Cutfield WS, Cundy T. Increasing prevalence of type 2 diabetes in adolescents. J Paediatr Child Health 2004;40:201–4.
  7. Evers IM, de Valk HW, Visser GHA. Risk of complications of pregnancy in women with type 1 diabetes: nationwide prospective study in the Netherlands. BMJ 2004;328:915–18.
  8. Worth R, Potter JM, Drury J, Fraser RB, Cullen DR. Glycosylated haemoglobin in normal pregnancy: a longitudinal study with two independent methods. Diabetologia 1885;28:76–9.
  9. The Diabetes Control and Complications Trial Research Group. Pregnancy outcomes in the Diabetes Complications Trial. Am J Obstet Gynecol 1996;174:1343–53.