At 27 weeks of pregnancy, would a slightly elevated amniotic fluid index (27) likely to be more from pre-existing, type 1 diabetes (concurrent A1c of 6.5) or from other causes?. At 23 weeks, the AFI was 22 so it developed within the past month. To date, there haven’t been any abnormalities on the ultrasound and the baby is normal weight.

Amniotic fluid volume is balanced between how much the baby is making from urination versus how quickly it is removed either by swallowing or absorption across the amniotic membranes. Swallowing accounts for most of the removal. Thus, any changes in those two variables will result in either an increase or decrease in the fluid volume. The amniotic fluid normally varies over the course of the pregnancy. The range for a normal amniotic fluid index is roughly 8 to 18 cm.

Increased amniotic fluid is commonly associated with all types of diabetes (type 1, type 2 and gestational). The cause is excess urine production due to increased fetal serum glucose. Even with good glucose control, the amniotic fluid can increase. Other causes are factors that would affect the passage of swallowed fluid into the fetal gastrointestinal system such as a tracheo-esophageal fistula or duodenal atresia. However, there is usually increased fluid early on in the pregnancy. Another infrequent cause would be if the baby just does not swallow well. This can be associated with neurologic problems or chromosomal abnormalities. Frequently, the cause of excess amniotic fluid cannot be determined.

In your case the excess fluid is most likely associated with diabetes, particularly if no structural abnormalities are noted on ultrasound.

OWJ