What Sustained Highs Mean for Your Baby
Reviewed by CDE Mehandi Sharma · Updated
This is the question behind most of the anxiety in GDM: what does a high reading do to my baby? The honest answer separates one reading from a pattern.
Glucose crosses the placenta. Insulin does not. So when your blood sugar runs high, your baby receives that extra glucose and responds by producing more of their own insulin to deal with it.
That extra insulin acts as a growth signal. Over weeks and months of sustained high readings, it drives extra growth — particularly around the abdomen and shoulders — which is what leads to a larger-than-expected baby.
The same mechanism explains something that surprises parents. A baby who has been making extra insulin for months keeps doing it briefly after birth, when the maternal glucose supply suddenly stops. That is why babies can have low blood sugar in their first hours and are checked for it.
The crucial word throughout is sustained. This is a process that works over weeks. One high reading after a wedding dinner does not do this, and treating every individual number as harm to your baby is both inaccurate and exhausting.
What matters is the trend across weeks — which is exactly what your readings and your growth scans are measuring, and why treatment gets adjusted rather than perfected.