Neural tube defects (NTDs) affect roughly 2 out of every 1,000 births worldwide, making them one of the most common types of serious birth defects. That translates to an estimated 214,000 to 322,000 affected pregnancies each year globally. In the United States, about 2,350 babies are born with some form of NTD annually, though rates have dropped significantly since the late 1990s thanks to folic acid fortification of grain products.
Types and Their Frequency
Not all neural tube defects occur at the same rate. Spina bifida, where the spinal column doesn’t fully close during early development, is the most common type, affecting about 1,300 babies per year in the U.S. Anencephaly, a fatal condition where major parts of the brain and skull don’t form, affects about 700 babies per year. Encephalocele, where brain tissue pushes through an opening in the skull, is the rarest of the three, affecting roughly 350 babies annually.
Rates in the United States by Ethnicity
NTD rates aren’t evenly distributed across populations. CDC data from 12 state-based birth defects tracking programs shows notable differences by ethnicity. Hispanic women have the highest rate of spina bifida at 3.80 per 10,000 live births. Non-Hispanic white women follow at 3.09 per 10,000, and non-Hispanic Black women have a rate of 2.73 per 10,000. The reasons for these disparities likely involve a combination of dietary patterns, genetic factors, and differences in access to prenatal vitamins and fortified foods.
How Rates Vary Around the World
Global variation in NTD rates is enormous. Some regions report fewer than 1 case per 10,000 births, while others see rates above 100 per 10,000. The Eastern Mediterranean region shows some of the widest ranges, from 2.1 to 124.1 per 10,000 births. The Western Pacific region has an even broader spread, from 0.3 to 199.4 per 10,000. Europe ranges from 1.3 to 35.9 per 10,000, and the Americas from 3.3 to 27.9 per 10,000.
Countries without mandatory folic acid fortification programs tend to have higher rates. Poverty, limited dietary diversity, and genetic predisposition in certain populations all contribute to these dramatic differences. Regions with both poor nutrition and no fortification policies consistently report the highest numbers.
How Folic Acid Fortification Changed the Numbers
The United States began requiring folic acid to be added to enriched grain products like bread, pasta, and cereal in 1998. The results were striking: NTD prevalence dropped by 19% to 32% overall, with the CDC reporting a 35% decline attributable to the fortification mandate. Canada saw similar reductions after implementing its own program. Mandatory folic acid fortification is now considered one of the most cost-effective public health interventions in existence.
Before fortification, NTD rates in the U.S. were considerably higher. The policy works because the neural tube forms very early in pregnancy, often before a woman knows she’s pregnant. Relying on individual supplement use alone misses many pregnancies, especially unplanned ones. Fortifying the food supply catches a much larger share of the population.
Who Is at Higher Risk
Several factors increase the chance of an NTD-affected pregnancy. The most well-established is insufficient folate intake before and during early pregnancy. Women who have already had one pregnancy affected by an NTD face a 2% to 3% recurrence risk in future pregnancies, which is roughly 10 times higher than the general population risk. Pre-existing diabetes, certain anti-seizure medications, and obesity have also been linked to elevated risk, though the exact degree varies.
The CDC recommends that all women who could become pregnant take 400 micrograms of folic acid daily. For women with a previous NTD-affected pregnancy, the recommendation jumps to 4,000 micrograms daily, starting at least one month before conception and continuing through the first three months of pregnancy. This higher dose has been shown to substantially reduce recurrence.
How NTDs Are Detected Before Birth
Most NTDs are now caught during routine prenatal care. A blood test measuring a protein called alpha-fetoprotein (MSAFP), typically done in the second trimester, detects about 95% of anencephaly cases and 65% to 80% of open spina bifida cases. However, this test has a false-negative rate of about 25% for open NTDs, meaning it misses roughly one in four.
Mid-trimester ultrasound performs better. Studies comparing the two methods found ultrasound detected 96% of NTDs, compared to 75% for the blood test alone. Two large clinical trials reported ultrasound sensitivity of 88% to 89% for NTDs. In practice, most providers use both screening methods together, which gives the best chance of early detection. Finding an NTD before birth allows families and medical teams to plan for specialized delivery and, in some cases of spina bifida, fetal surgery to repair the defect before birth.