Current management of diabetic pregnancy

OBG Management. 2005 October;17(10):16-31

October 1, 2005|OBG Management

Unlike conventional therapy, intensive drug therapy plus self-monitoring diminishes adverse obstetric outcomes in all types of diabetes

Using these standards, 30% to 50% of women with gestational diabetes require pharmacologic therapy when diet alone fails to reduce glucose levels.

Determining insulin requirements

The insulin algorithm for women with gestational diabetes is based on prepregnancy BMI:

For women with a BMI of 25 and less, the insulin dose is 0.8 U/kg.
For women with a BMI of more than 25 (overweight and obese), it is 1.0 U/kg.

For example, a woman at 28 weeks’ gestation who currently weighs 85 kg and who is classified as overweight or obese on the basis of her prepregnancy BMI, would be given an insulin dose of 85 U (85 kg×1 U).

Once the total insulin dose is calculated, it is divided so that two thirds is administered in the morning and one third in the afternoon or evening. The morning dose is further divided in a ratio of 2 to 1 (intermediate and rapid-acting) and the evening dose into a ratio of 1-to-1 (rapid-acting and intermediate). The rapid-acting dose is administered with the evening meal, while the intermediate dose is given just before bedtime.

If the patient with gestational diabetes has not achieved the desired level of glycemic control after 3 to 7 days, increase the total dose by 10% to 20% and thereafter adjust it when needed.

Fine points of insulin therapy

The actual total insulin dose in women with gestational diabetes is 40% higher than the calculated dose¹⁶; this provides a margin of safety and avoids severe hypoglycemic episodes. As a rule of thumb, self-monitoring of blood glucose is necessary before every administration of insulin.

The failure to introduce insulin therapy in a timely fashion may lead to fetal hyperinsulinemia and associated complications. Conversely, premature initiation of insulin in women who could have achieved glycemic control with diet alone leads to unnecessary drug treatment.

When gestational diabetes is diagnosed after 30 to 33 weeks’ gestation and there is little time left to gain the desired level of control, pharmacologic intervention is recommended. There is greater flexibility when gestational diabetes is diagnosed early in the third trimester.

Which form of insulin is best?

Human insulin is recommended when insulin is prescribed during pregnancy, and the same type of insulin is used for pregestational and gestational diabetes. The main differences:

use of the insulin pump in type 1 diabetes and
the insulin dose, which is based on insulin requirements for each type of diabetes.

The most common form of insulin today is biosynthetic human insulin. Short- or rapid-acting insulin is administered before meals to reduce glucose elevations associated with eating. Longer-acting forms are used to contain hepatic glucose production between meals and during fasting.

Regular insulin and insulin lispro are the 2 most common rapid-acting forms of insulin in use.

Pros and cons of insulin lispro

Mounting evidence of the benefits of insulin lispro for type 1 and type 2 diabetes in nonpregnant individuals includes:

fewer episodes of severe hypoglycemia,
limited postprandial glucose excursions, and
a possible decrease in glycosylated hemoglobin when the drug is administered by continuous subcutaneous infusion.²³

Insulin lispro also offers greater convenience in the timing of administration: Analogs can be administered up to 15 minutes after the start of a meal, in contrast to soluble insulin, which must be taken 30 minutes before the meal.

Neither the American Diabetes Association²² nor the American College of Obstetricians and Gynecologists¹⁹ endorses the use of insulin analogs. The reason: these drugs have not been adequately tested in pregnancy, although insulin lispro is categorized as a class B drug.

Data on insulin lispro are limited and abstracted from studies with relatively small sample sizes (only 244 gravidas reported thus far in the literature). Most case reports describe improved glycemic control, increased patient satisfaction, and fewer hypoglycemic episodes, but lack sufficient data on maternal and neonatal outcomes. Even so, many obstetricians have administered the drug with no adverse outcome.

In my opinion, insulin lispro can and should be used in pregnancy because of its ability to produce more physiologic insulin patterns and because the data against it are anecdotal. In contrast, insulin aspart and glargine should be avoided in pregnancy because data on their effects are limited.^24-40

Individualizing the insulin regimen

A relatively high dose of insulin (about 50–90 U) is needed to achieve glycemic control in gestational diabetes. In contrast, in type 1 diabetes, a lower dose is necessary (50–60 U). Because of the different glycemic profile of women with type 1 diabetes, individualizing the insulin regimen is accepted practice.

References

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