Does Gestational Diabetes Cause Holoprosencephaly?

If you had gestational diabetes during your pregnancy and your child was diagnosed with holoprosencephaly (HPE), the most important thing for you to know is that your gestational diabetes did not cause your baby’s condition. Maternal guilt is a heavy and common burden for parents of children with HPE. However, a metabolic condition that develops later in pregnancy cannot alter brain structures that formed during the earliest weeks.

The Timing of Brain Development vs. Gestational Diabetes

To understand why gestational diabetes does not cause HPE, it is helpful to look at the timeline of fetal development.

Holoprosencephaly occurs when the embryonic forebrain (the prosencephalon) fails to completely divide into right and left hemispheres ^[1][2]. This critical step of brain development is known as cleavage—imagine a single, round structure that needs to split down the middle to form two separate halves. This process happens extremely early in pregnancy, primarily between the 4th and 6th weeks of gestation ^[1][3].

Gestational diabetes, on the other hand, typically develops later in pregnancy and is usually diagnosed during standard screening between 24 and 28 weeks ^[4][5]. By the time gestational diabetes alters blood sugar levels in the mother’s body, the window for the baby’s forebrain to divide has already closed months prior. Because of this timeline, gestational diabetes is biologically incapable of causing HPE.

Pre-Existing Maternal Diabetes as a Risk Factor

You may have read online or in medical records that “maternal diabetes” is a risk factor for holoprosencephaly. This frequently causes confusion and self-blame among parents. When medical literature refers to this risk, it is specifically talking about pre-gestational diabetes—meaning Type 1 or Type 2 diabetes that existed before the pregnancy began ^[6][7].

When a mother has pre-existing, suboptimally controlled diabetes during the very first weeks of pregnancy, elevated blood sugar is present exactly when the fetal brain is beginning to form. Studies show that pre-gestational diabetes is a non-genetic risk factor that can increase the chance of HPE ^[8].

If you had pre-existing diabetes, it is crucial to know that the absolute risk of your baby developing HPE remains extremely low. The vast majority of mothers with diabetes have babies without HPE. Furthermore, even in cases of pre-existing diabetes, it is rarely the sole cause. HPE is a complex condition, usually resulting from a combination of genetic factors and specific, rare environmental factors ^[9][10]. (In this context, “environmental factors” refers to complex interactions like genetic mutations combined with rare high-risk medications or severe infections—not normal daily activities, standard diets, or household cleaning products.)

Letting Go of the Guilt

Gestational diabetes has a distinctly different risk profile than pre-existing diabetes, and it is associated with far fewer types of congenital anomalies ^[8]. If your diabetes developed during pregnancy rather than existing beforehand, it was not present when the brain was undergoing cleavage.

There is nothing you could have done differently to change the way the embryonic brain divided during those first few weeks. As you navigate your child’s care, understanding this timeline can help you shift your focus from questioning the past to working with your care team to advocate for your child’s future.