How Low Can a Pregnant Woman Go?

I am 28 years old and I’ve had juvenile diabetes for 21 years. I want to try for a family. I’m concerned about my frequent dropping out with low blood sugars at any given time, for a hundred different reasons (hormone levels is one). My big question is, how low can your blood sugars go before it starts to harm a fetus? Or, is it a matter of how long you have a low blood sugar?

Thank you for your time.

Kimberly Ashworth


Maternal hypoglycemia does not harm the fetus as much as maternal hyperglycemia, which leads to congenital malformation and/or stillbirth.

Hypoglycemia, especially at night, is a common concern during early pregnancy. This reaction is caused by metabolic changes secondary to a loss of glucose and gluconeogenic substrates (by-products of protein digestion) to the fetus, which cause maternal lows.

Low reactions may result from the tight control needed to sustain near-normal glucose values. The issue that arises is maternal unawareness of the symptoms, due to lowered thresholds. Since the average glucose levels are lower than usual, the symptoms of weakness, palpitations, tremors, etc., may not appear at 50 to 60 mg/dl, but rather at lower values, like 30 to 40 mg/dl. Levels this low lead to a severe hypoglycemic response, leaving the pregnant woman to experience confusion, seizure or even coma. If severe hypoglycemia is left untreated and the safety of the mother is jeopardized, the fetus may be in danger.

Pregnant women with type 1 diabetes should frequently check their glucose levels in order to avoid asymptomatic hypoglycemia. An ideal testing frequency is eight times per day. These would consist of:

  • once before each meal, for the assessment of asymptomatic hypoglycemia
  • one hour after each meal, for the evaluation of the effect of a particular meal and insulin doses
  • bedtime, to determine reactions and their appropriate treatment
  • during the middle of the night, to detect hypoglycemia.=

Target ranges for each test are patterned after maternal plasma glucose levels in a normal pregnancy:

  • fasting glucose: 60-90 mg/dl
  • premeal glucose: 60-105 mg/dl
  • 2 to 6 a.m.: 60-120 mg/dl

The prevention of asymptomatic hypoglycemia depends on maintaining blood glucose values in the near-normal ranges through frequent self-monitoring and insulin adjustment. Appropriate dietary management is also vital to provide adequate nutrition for both mother and fetus. This plan will help promote a healthy and successful outcome for the pregnancy.

Loretta Hothersall, MSN, RNS, CS, RNPC
Maine Center for Endocrinology and Diabetes
Scarborough, Maine

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