What Causes Aplasia Cutis Congenita During Pregnancy?

If your baby was recently diagnosed with aplasia cutis congenita (ACC), it is completely normal to ask yourself, “Did I do something to cause this?” The short and most important answer is no. ACC—a rare condition where a baby is born missing a small patch of skin, most commonly on the scalp ^[1]—is almost always a chance occurrence ^[2]. It is not caused by what you ate, how much you exercised, a stressful event at work, or typical pregnancy activities.

To help ease your mind, it helps to understand the actual biological mechanisms that doctors believe cause this condition. ACC happens when the skin either fails to form completely or is disrupted while the baby is developing in the womb ^[2]. Here is what the medical research tells us about why this happens.

Interruptions in Blood Flow (Vascular Disruption)

One of the most widely accepted theories for why ACC occurs is a sudden, temporary drop in blood flow to a specific area of the baby’s developing skin ^[3][4]. If a tiny patch of tissue does not receive a steady supply of oxygen and nutrients for a brief moment, it can stop growing ^[5]. This is considered a random developmental glitch, much like a hiccup during the complex process of forming a baby.

Vanishing Twin Syndrome

Sometimes, a pregnancy begins with twins, but one twin stops developing very early on and is absorbed into the womb. This is known as “vanishing twin syndrome” or fetus papyraceus ^[6]. Often, a mother never even knows she was originally carrying twins. The loss of this twin can cause rapid blood pressure changes or vascular disruptions in the surviving baby, which is strongly linked to a specific pattern of ACC known as Type V ^[3][4]. Unlike the more common scalp ACC, this type usually presents on the baby’s trunk or limbs ^[6]. It is important to know that aside from the skin patch, the surviving baby is typically perfectly healthy.

Exposure to Specific Medications

The vast majority of standard medications, including prenatal vitamins and over-the-counter pain relievers, do not cause ACC. However, there is a known link between ACC and methimazole, a prescription drug used to treat an overactive thyroid (hyperthyroidism) ^[7][8]. If a mother takes methimazole during the first trimester, it can sometimes interfere with the baby’s skin development. Because of this, doctors often switch pregnant patients to alternative thyroid medications, like propylthiouracil, early in pregnancy to reduce this risk ^[9].

Viral Infections During Pregnancy

In very rare circumstances, contracting specific viral infections while pregnant can affect the baby’s skin. The most notable example is varicella (the virus that causes chickenpox and shingles). A varicella infection during pregnancy can leave scars or defects on the baby’s skin that present as ACC when they are born ^[10]. Other viruses, such as Hepatitis B, have also been associated with the condition in isolated cases ^[11].

Genetics and Underlying Syndromes

While the vast majority of ACC cases are isolated events meaning the baby is otherwise completely healthy, some instances are tied to a baby’s unique genetic code ^[12]. Certain genetic variations or syndromes, such as Adams-Oliver syndrome or Trisomy 13, include ACC as one of their symptoms ^[13][14].

Please do not panic if you see these syndromes mentioned online. Syndromic ACC almost always presents alongside other major, obvious medical issues (such as heart, limb, or neurological differences) that your pediatrician would likely identify immediately ^[15]. If your baby only has a missing patch of skin, it is highly likely to be an isolated, chance occurrence.

Looking Forward: What Does This Mean for My Baby?

Knowing why this happened does not answer your most pressing question: what happens next? The good news is that many smaller ACC lesions, especially those limited just to the skin, heal wonderfully on their own with conservative, gentle wound care ^[1][16]. For larger patches or those that involve deeper tissues, your care team may discuss surgical options to help close the area safely ^[17]. You will likely work with a multidisciplinary team—which may include a pediatrician, a pediatric dermatologist, or a plastic surgeon—to create a daily care plan that keeps your baby comfortable, prevents infection, and supports healing ^[18].