Background

Spina bifida without anencephalus (hereafter referred to only as spina bifida) is a neural tube defect or brain disorder that results in an incomplete formation of the brain, spinal cord, or meninges (protective covering around the brain and spinal cord). The most serious type results in a sac of fluid protruding through an opening in the infant’s back. Spina bifida can cause minor or severe physical and mental disabilities depending on the size and location of the malformation. Complications of spina bifida can include learning disabilities, such as challenges with language and reading comprehension, and loss of muscle function and sensation. Physical disabilities can occur as well, such as deformed feet, uneven hips, and a curved spine. Although the symptoms and complications of spina bifida can be severe, it is important to note that most individuals with this condition have normal intelligence. In fact, the most common forms of this condition, called occulta, is also the mildest and rarely causes disability or symptoms.[1]

Although some risk factors have been identified, family history of neural tube defects, and maternal obesity, and girls are more likely to be affected than boys, the exact causes of spina bifida are unknown.[2] However, there is strong evidence that folic acid supplementation, through diet or taking vitamins, before and during early pregnancy can reduce the risk of having a baby with spina bifida.[3]

Epidemiology

Alaska Birth Defects Registry (ABDR) registers birth defects as reported from health care providers using International Classification of Disease (ICD) billing codes. The use of these ICD codes can lead to misclassification of diagnosed conditions. Prior to this report, all prevalence estimates were based on the number of unique children reported to ABDR with an ICD code representing a specified condition regardless of case confirmation status.

The estimates in this report were derived by conducting medical record review and case confirmation of a random sample of cases of the condition reported to ABDR. The confirmation probability from the sample was used to develop informed estimates of the actual diagnosed defect prevalence. See Defect prevalence calculation.

For explanations of table columns see Column descriptions.

Prevalence

Spina bifida occurs in 3.5 out of every 10,000 live births in the United States. This results in about 1,460 babies diagnosed with spina bifida each year.[4]

In Alaska, during 2007-2015, the prevalence of spina bifida was 3.1 per 10,000 live births.
Reports Defects Births Prevalence (95% CI)
Total 43 31.9 101978 3.1 (2.1, 4.3)
Notes: 95% CI = 95% Confidence Interval

Trend

Prevalence per 10,000 births of spina bifida during 2007-2015 by three-year moving averages, with 95% confidence interval band and Poisson estimated fitted line.
Reports Defects Births Prevalence (95% CI) Predicted Prevalence†
2007-2009 4.7 3.5 11261.7 3.1 (1.2, 8.1) 2.4
2008-2010 3.0 2.5 11404.0 2.2 (0.7, 6.7) 2.5
2009-2011 3.7 2.9 11404.7 2.5 (0.8, 7.2) 2.6
2010-2012 3.3 2.7 11354.0 2.4 (0.7, 6.8) 2.7
2011-2013 2.7 2.3 11349.0 2.0 (0.4, 5.9) 2.8
2012-2014 4.0 3.1 11334.7 2.7 (0.7, 6.8) 2.9
2013-2015 6.3 4.5 11377.0 4.0 (1.4, 8.5) 3.0
Notes: Each row is based on three-year moving averages; Prevalence reported per 10,000 live births; 95% CI=95% Confidence Interval

† Estimated rate based on Poisson model
The p-value test for trend detected no significant increase or decrease in the number of live births with spina bifida during 2007-2015. See p-value estimate
Estimate Std. Error t value Pr(>|t|)
0.04163 0.04495 0.92625 0.39682

Regional Distribution

Distribution of spina bifida in Alaska by Public Health Region of maternal residence at the time of birth. A description of regional breakdowns can be found here. Data suppressed for # of reports < 6.
Reports Defects Births Prevalence (95% CI)
Anchorage 11 9.1 41815 2.2 (1.1, 4.1)
Gulf Coast 7 4.6 6313 7.2 (2.6, 16.2)
Interior 10 7.1 18534 3.8 (1.9, 7.8)
Mat-Su - - 12081 -
Northern - - 7114 -
Southeast - - 6375 -
Southwest 7 4.8 9746 4.9 (1.7, 10.5)
Notes:Prevalence reported per 10,000 live births; Data suppressed for # of reports < 6; 95% CI = 95% Confidence Interval

Demographics

Some subgroups may be more at risk for having a baby with spina bifida. This section provides the descriptive epidemiology of specified maternal, birth, and child characteristics identified from the birth certificate.

Reports Defects Births Prevalence (95% CI)
Sex
  Female 22 16.1 49462 3.3 (2.0, 5.2)
  Male 21 15.7 52516 3.0 (1.7, 4.7)
Birth weight (grams)
  <2500 9 5.7 5925 9.7 (3.7, 19.7)
  2500+ 34 26.2 95890 2.7 (1.9, 4.0)
Maternal age
  12-19 - - 8043 -
  20-24 12 8.9 28015 3.2 (1.5, 5.6)
  25-29 11 8.4 30852 2.7 (1.3, 5.1)
  30-34 9 6.7 22480 3.0 (1.2, 5.8)
  35-39 7 4.8 10015 4.8 (1.6, 10.2)
  40+ - - 2543 -
Maternal race
  Alaska Native/American Indian 17 11.7 25801 4.5 (2.4, 7.6)
  Asian/Pacific Islander - - 9399 -
  Black - - 4134 -
  White 21 16.3 61287 2.7 (1.6, 4.2)
Maternal education (years)
  <12 6 4.2 9778 4.3 (1.7, 10.5)
  12 18 13.0 36724 3.5 (1.9, 5.7)
  12+ 18 13.9 52380 2.7 (1.5, 4.2)
Marital status
  Married 22 17.1 64510 2.6 (1.6, 4.2)
  Unmarried 21 14.8 37078 4.0 (2.3, 6.3)
Maternal smoking use
  Reported smoking 8 5.7 14467 3.9 (1.5, 8.1)
  Reported not smoking 34 25.5 85927 3.0 (2.0, 4.3)
Medicaid (mother or child)
  Medicaid 33 22.8 51554 4.4 (2.8, 6.5)
  non-Medicaid 9 8.5 50311 1.7 (0.8, 3.1)
Father on birth certificate
  None - - 5559 -
  Present - - 96419 3.2 (2.2, 4.4)
Notes: Prevalence reported per 10,000 live births; Data suppressed for # of reports < 6; 95% CI = 95% Confidence Interval

Technical notes

Column descriptions

# Reports: Unless otherwise noted, the number of unique reports of the defect received by ABDR during the specified birth year(s). Each report represents a unique child with the specified defect.

# Defects: The estimated true number of reports that are diagnosed defects based on medical record review and case confirmation.

# Births: The number of live births among Alaskan residents that occurred in Alaska during the specified birth year(s).

Prevalence (95% CI): The estimated diagnosed prevalence of the condition and corresponding 95% Confidence Interval. (For information on how the defect prevalence was estimated see below).

Defect prevalence calculation

The estimated defect prevalence was calculated using a Bayesian approach based on the reported prevalence, PPV and 1-NPV (see formula below).

Through medical records review and case confirmation of a random sample of reported cases, the defect prevalence is calculated as:

\[PPV (Positive Predictive Value) = p(defect|report)\] \[NPV (Negative Predictive Value) = p(\overline{defect}|\overline{report})\]

\[p(defect) \approx [p(report)\cdot PPV]+[p(\overline{report})\cdot (1-NPV)]\]

Defect prevalence estimates are a more accurate estimation of the actual diagnosed prevalance of birth defects compared to the reported prevalance estimates in Alaska. ABDR obtains reports from medical providers using International Classification of Disease (ICD) codes that are extracted from individual systems which when aggregated may not reflect true diagnostics. Caution should be used when interpreting and comparing the reported prevalence estimates with national estimates.

See Data analysis methods for more information.

P-value estimate

To evaluate the trend over time and account for under/over-dispersion we constructed a quasi-Poisson regression model. This model assumes the variance is a linear function of the mean and models the estimated number of annual defects by year with a natural log (ln) offset of the annual births. P-values < 0.05 are considered significant, which indicates that the predicted slope is significantly different from a slope of zero.

Data suppression

For region and demographic data tables, values are suppressed based on the number of reports received during the observation period. Counts less than 6 are suppressed (as indicated by ‘-’ in the table). For regions or demographics with only one cell count suppressed a second is suppressed to eliminate the ability to back-calculate the estimate.

References

[1] Centers for Disease Control and Prevention. Spina Bifida, https://www.cdc.gov/ncbddd/spinabifida/facts.html; 2016 [accessed 02.28.2017]

[2] Agopian A.J, Tinker SC et al. Proportion of neural tube defects attributable to known risk factors. Birth Defects Research Part A: Clinical and Molecular Teratology 2013; 97(1): 42-46

[3] Grosse SD, Berry RJ et al. Retrospective Assessment of Cost Savings From Prevention: Folic Acid Fortification and Spina Bifida in the U.S. Am J Prev Med 2016; 50 (4 Suppl 1): S74-80.

[4] Centers for Disease Control and Prevention, Birth Defects Data and Statistics, https://www.cdc.gov/ncbddd/birthdefects/data.html; 2016 [accessed 02.23.2017]

Suggested Citation

State of Alaska Department of Health and Social Services, Division of Public Health, Section of Women’s, Children’s, and Family Health. Alaska Birth Defects Registry Condition Report: Spina Bifida, Alaska, 2007-2015. Updated January 1, 2020. Available at: http://rpubs.com/AK_ABDR/SpinaBifida07_15.

Contact

Alaska Birth Defects Registry (ABDR)
3601 C Street, Suite 358
Anchorage, AK 99503
(907) 269-3400 phone
(907) 754-3529 fax

Updated: January 1, 2020
Code source: R:\ABDR\Analysis_New\ABDR_CASECONF\cond_reports\Published_reports\SpinaBifida07_15.Rmd