Although I have left the discussion of pregestational diabetes until the end of our series on “Diabetes in Pregnancy,” that was not done with the intent of diminishing its significance with regard to maternal and fetal morbidity and mortality. Even though pregestational diabetes only comprises about 4-5% of the diabetes we manage during pregnancy, it probably contributes to more significant complications for mothers and babies and to the overall cost of medical care than all of the gestational diabetes detected early in the third trimester. We have often said that the best prenatal care begins prior to conception and almost nowhere is that more true than under circumstances in which a woman has pregestational type 1 (or type 2) diabetes.
I see several major goals of management of the pregestational diabetic: • Reduce the risk of early fetal wastage • Reduce the risk of fetal malformations • Reduce the risk of progression of maternal ‘end-organ’ disease (e.g., kidney, eye, and cardiovascular disease) • Reduce the risk of pregnancy complications such as preeclampsia, urinary tract infections, and premature labor and delivery • Reduce the risk of epigenetic ‘programming’ of the baby’s metabolic pathways • Reduce the risk of fetal damage and loss in later gestation • Reduce the risk of fetal macrosomia • Reduce the risk of traumatic delivery • Reduce the risk of neonatal complications such as hypoglycemia, hyperbilirubinemia, and pulmonary immaturity
To have the greatest impact on all of the above, preconceptional counseling and care, aggressive, ongoing maternal management, and fetal assessment and surveillance throughout the pregnancy are required. A pregestational diabetic should not wait until she has a confirmed pregnancy to see her doctor. Fetal wastage (miscarriages) and major fetal malformations are directly related to the degree of mother’s blood sugar control in early pregnancy. Poorly-controlled diabetics can have 3 to 10 times the fetal malformation rates of nondiabetic women and numerous studies have proven that diabetic women with normal blood sugars during the embryonic period have no higher rate of fetal abnormalities than nondiabetic women.
Major fetal abnormalities now account for 20-50% of the perinatal deaths accompanying pregnancies of pregestational diabetics. Although there is no specific ‘diabetic syndrome’, the most common congenital malformations include neural tube, heart, skeletal, and abdominal wall defects. An unusual condition called ‘caudal regression syndrome’, associated with poor development of the lower fetal spine and severe structural abnormalities below the waist, is rarely seen in babies of nondiabetic women (Kucera, et al., J Reprod Med 1971;7:73-82). The reason preconceptional care is so important is that these malformations can occur as the result of poor control of blood sugars within two weeks after the first missed menstrual period signaling pregnancy (for example, the neural tube should be completely closed by day 26 following conception).
Another reason preconceptional evaluation and care is important is that it provides the opportunity to identify and optimize therapy for other medical problems, related and unrelated to the diabetes, that may put both mother and baby at risk for complications during a pregnancy. For example, long-standing, poorly-controlled diabetes is often accompanied by kidney damage (diabetic nephropathy), eye damage (retinopathy), atherosclerotic disease, hypertension, as well as peripheral and autonomic neuropathies. When these conditions are present, pregnancy can increase progression of these ‘end-organ’ problems and the presence of these underlying defects themselves are red flags for risks associated with pregnancy complications such as preeclampsia, intrauterine growth restriction, preterm delivery, stillbirths, and infectious complications during pregnancy. Type 1 diabetics are also at increased risk for thyroid disease (also autoimmune in origin) at a rate about three times that of the general population.
With all that said and done, in addition to the routine pregnancy laboratory studies, and counseling regarding nutrition, exercise, self-monitoring and expected levels of blood sugar control we have discussed in earlier posts in this series, any woman with pregestational diabetes should have at least the following studies done, preconceptionally, or as early in pregnancy as possible, to establish a reference baseline for counseling and follow-up evaluation during the pregnancy:
• Complete physical examination • Ophthalmologic examination • 24 hour urine for protein and creatinine clearance • Hemoglobin A1c • Thyroid stimulating hormone • Fasting lipid profile • Electrocardiogram with any evidence of vascular disease by history or physical exam and in all with diabetes > 10 years duration
If one is fortunate enough to see the woman for preconceptional counseling, once the laboratory results are available, any new problems (e.g., thyroid disease, hypertension) should be addressed medically in preparation for pregnancy. In addition, I will usually recommend a prenatal vitamin, supplemental folic acid (2-4 mg per day) as a means, perhaps, of reducing certain congenital birth defects, as well as low-dose aspirin (81 mg per day), particularly for those with long-standing diabetes or evidence of vascular disease.