In about 7% of pregnancies, the mother has high blood sugar that was not present before pregnancy. When this occurs it is called Gestational Diabetes (GD). This generally occurs after 24 weeks, and is treated by controlling carbohydrate intake, monitoring blood sugar levels and if necessary, insulin injections.
GD is detected through a glucose tolerance test. However, the results of the test are not reproducible 50-70% of the time which causes concern among some experts. Also, the small increase in perinatal mortality that is associated with an abnormal glucose tolerance test can be predicted equally well by the indications for the test (obesity, large fetus and other indicators).
Why is this a labor challenge?
Although the mother experiencing GD may have no symptoms, unless she is monitoring her blood sugar levels there will be concern the baby is getting high levels of blood glucose. Elevated blood glucose can cause the baby to develop macrosomia, a condition in which the baby's body is large with the weight particularly distributed through the trunk and shoulders. This large size can make it difficult for the baby to navigate through the pelvis and is associated with shoulder dystocia. At this time, there is not a conclusive way to determine the size of the baby before it is born, however it is believed that by following a carefully controlled diet and monitoring blood sugar levels the risks for macrosomia are significantly reduced.
Up to 30% of the mothers who have abnormal glucose tolerance tests will have a baby whose birth weight is above 4000 grams. The majority of macrosomia occurs among babies whose mothers had normal results on the glucose tolerance test. There is no evidence that treatment for women with an abnormal glucose tolerance test reduces problems related to high glucose levels. Insulin and diet changes only decrease the incidence of macrosomia, they do not affect the other outcomes such as cesarean surgery, shoulder dystocia or death.
Concerns about the validity of the glucose tolerance test and the lack of evidence of improved outcomes for mothers treated for Gestational Diabetes has lead to some very strong language used in the Guide to Effective Care in Pregnancy and Childbirth, "Until the risk of minor elevations of glucose during pregnancy have been established in appropriately conducted trials, therapy based on this diagnosis must be critically reviewed. The use of injectable therapy on the basis of the available date is highly contentious and in many other fields of medical practice, such aggressive therapy without proven benefit would be considered unethical."
If macrosomia is suspected or if non-stress tests indicate your baby is showing signs of not handling contractions well, your caregiver may recommend elective induction before your due date. Some caregivers feel that by causing the baby to be born 2 weeks early, the baby has a better chance of fitting through the pelvis. Induction may require some adjustments in your natural birth plans; however it may still be possible to give birth without using pain medications.
Maintain healthy blood sugar levels during pregnancy to prevent macrosomia.
Monitor blood sugar levels to ensure diet and exercise changes are effective.
Things to discuss with your caregiver:
The option of cesarean surgery increases the risks for the mother without any evidence of benefit for the baby. Be sure you know how your caregiver prefers to handle birth when gestational diabetes is suspected.
In some women, diet and exercise changes alone are not able to control blood sugar levels. If this happens to you, your caregiver may recommend insulin injections to maintain appropriate blood sugar levels. To ensure the safety of you and your baby, it may be necessary to monitor blood sugar levels during labor, however this monitoring does not need to interfere with your plans for a natural birth. Discuss the options that are available for this with your caregiver.
References:The Merk Manual 16th Edition. 1992. Robert Berkow, MD (ed.). Merk Research Laboratories.
Enkin, Keirse, Nilson, Crowther, Duley, Hodnett and Hofmeyr. A guide to effective care in pregnancy and childbirth Third Edition. 2000. Oxford: Oxford University Press.
Complete Book of Pregnancy and Baby's First Year. 1994. Robert V. Johnson, MD (ed.). William Morow and Company, Inc.
Irion O, Boulvain M. Induction of labour for suspected fetal macrosomia (Cochrane Review). In: The Cochrane Library, Issue 1, 2004. Chichester, UK: John Wiley & Sons, Ltd.
Special thanks to diabetes educator Hope Mikat for her assistance in describing the challenges that face a woman with gestational diabetes who wants to have a natural birth.