The relationship between falling insulin requirements and serial ultrasound measurements in women with preexisting diabetes: a prospective cohort study.

Introduction: A large fall in insulin requirements (FIR) in women with diabetes is associated with adverse clinical outcomes but previous studies have not examined its relation with serial ultrasound parameters.

Objective: To determine whether FIR is associated with alteration in umbilical artery Doppler parameters and fetal growth restriction (FGR) in women with preexisting diabetes.

Methods: Serial obstetric Doppler ultrasounds were conducted 2 weekly from 28 weeks gestation in women with Type 1 and Type 2 diabetes who were being treated with insulin. Estimated fetal weight (EFW), head circumference:abdominal circumference (HC:AC) ratio and umbilical artery doppler parameters ( ratio) and pulsatility index (PI) were measured. Information on insulin dose was collected prospectively throughout pregnancy and women with FIR ≥ 15% were considered cases. Linear mixed effect models were used to assess the association between FIR and ultrasound parameters.

Results: One hundred and forty two women were included in the study (type 1 diabetes  = 41, type 2 diabetes  = 101). Thirty women demonstrated FIR ≥ 15%. There was no significant difference in the change of S/D ratio or PI over the third trimester in cases with FIR ≥ 15%, compared to the rest of the cohort, before or after adjusting for type of diabetes. Likewise there was no difference in EFW and HC:AC ratio with advancing gestation before or after adjusting for variables known to influence fetal growth. FGR rates (3.3 vs 8%  = 0.298) and high S/D ratio > 95% (13.3 vs 8%,  = 0.296) were similar between the two groups.

Conclusions: FIR ≥ 15% was not associated with changes in placental flow or FGR however larger studies are needed to evaluate this further.