Congenital Malformations Registry - Summary Report

Section VI
Current Topics

NTD Surveillance and Trends

In 1992, the United States Public Health Service first recommended that all women capable of becoming pregnant take folic acid to prevent neural tube defects (NTD).1 This recommendation was based on study results including clinical trials showing that folic acid supplementation taken before becoming pregnant and through the first trimester of pregnancy reduced the risk of having an infant affected with an NTD by 50% for both first pregnancies and those following NTD-affected pregnancies 2,3 Recognizing its importance, the fortification of folic acid to grain products as a public health intervention was mandated by the United States Food and Drug Administration in 1998. Studies that involved at least twenty-three population based surveillance systems across the United States, including New York State, looked at rates of NTD-affected pregnancies before and after the mandated fortification and concluded that there was a decline in NTD-affected pregnancies, especially those diagnosed with spina bifida.4

New York State has mounted a multi-faceted approach to this public health problem. A major campaign to get information to physicians and the public was initiated in 1996. Knowledge about and use of folic acid is tracked with the PRAMS (Pregnancy Risk Assessment Monitoring System) and the BRFSS (Behavioral Risk Factor Surveillance System), and New York's NTD surveillance system allows us to monitor changes in NTD occurrence.

Since 1996, the Congenital Malformations Registry (CMR) has had an intensive surveillance system for NTDs in seven counties of the Lower Hudson Valley (HSA 6) where about 30,000 births occur yearly. A major problem with accurately describing the prevalence of NTD-affected pregnancies is that many surveillance systems only ascertain live born infants. This presents a problem since many NTD-affected pregnancies are diagnosed prenatally; therefore, pregnancies resulting in fetal death or elective termination are not counted. Widespread use of prenatal ultrasound and blood tests has led to increased detection and termination of NTD-affected pregnancies.6 The CMR NTD surveillance actively ascertains cases, using hospitals, health care providers and termination facilities. The surveillance goes back retrospectively to 1990, and since 1996 ascertainment has been prospective. For 1990 to 2001, a total of 231 cases of NTD-affected pregnancies have been identified. For the same time period, only 114 cases were reported to the CMR, which includes only live born cases. The percent of NTD-affected pregnancies that have been terminated in HSA 6 is shown in Figure 1. Termination of NTD-affected pregnancies continued to increase from 23% in 1990 to over 50% in 2003 in that region of the state. As terminations increase, ascertainment by passive surveillance systems like the CMR will greatly underestimate the occurrence of neural tube defects.

The rates per 1,000 births of anencephaly, spina bifida, and total NTD found by the active surveillance in HSA Region 6 and based on CMR reports are displayed in Figures 2, 3 and 4. The difference in ascertainment of these defects by the two surveillance systems is quite evident. Also presented are three-year moving average trend lines. These indicate that the rates of NTD-affected pregnancies have decreased by 22% over time. Since New York's campaign to educate the medical community and women of childbearing age of the benefits of folic acid consumption coincided with mandated fortification of grain products, it is difficult to attribute the decrease seen in NTD-affected pregnancies to one prevention measure. However, since NTDs are potentially preventable and NTD-affected pregnancies are still occurring, continued education and surveillance will only benefit the public.

The figures are all available in the complete Congenital Malformations 1998-2001 Annual Report which is available as an Adobe Portable Document Format (PDF, 903KB, 81pg).

  1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Anencephaly (NTD surveillance) 57.14 57.14 20.00 60.00 50.00 100.0 50.00 55.56 100.0 83.33 66.67 83.33 60.00 25.00
Spina Bifida (NTD surveillance) 8.33 7.69 8.33 33.33 0.00 20.00 54.55 42.86 16.67 50.00 62.50 22.22 66.67 83.33
Total NTD (NTD surveillance) 23.08 23.08 15.00 45.00 26.32 47.06 48.00 50.00 50.00 58.82 60.00 50.00 54.55 54.55
Anencephaly (NTD surveillance) 0.22 0.22 0.16 0.33 0.27 0.13 0.34 0.31 0.17 0.21 0.20 0.20 0.17 0.14
CMR Anencephaly 0.06 0.06 0.03 0.07 0.07 0.00 0.07 0.00 0.00 0.03 0.00 0.03 * *
Spina Bifida (NTD surveillance) 0.38 0.41 0.39 0.30 0.30 0.34 0.38 0.24 0.21 0.35 0.27 0.31 0.31 0.21
CMR Spina Bifida 0.25 0.41 0.23 0.10 0.40 0.24 0.21 0.14 0.14 0.21 0.07 0.31 * *
Total NTD (NTD surveillance) 0.82 0.83 0.65 0.66 0.63 0.57 0.85 0.62 0.41 0.59 0.50 0.54 0.75 0.38
CMR Total NTD 0.44 0.64 0.26 0.20 0.53 0.24 0.38 0.17 0.14 0.28 0.17 0.34 * *

* CMR data only available through 2001


  1. Center for Disease Control. Recommendations for the use of folic acid to reduce the number of cases of spina bifida and other neural tube defects. MMWR 1992;41:1-7.
  2. MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council vitamin study. Lancet 1991;338(8760):131-37.
  3. Czeizel AE, Dudas I. Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. NEJM 1992;327(26):1832-35.
  4. Williams LJ, Mai CT, Edmonds LD, Shaw GM, Kirby RS, Hobbs CA, Sever LE, Miller LA, Meaney FJ, Levitt M. Prevalence of spina bifida and anencephaly during the transition to mandatory folic acid fortification in the United States. Teratology 2002;66:33-9.
  5. Center for Disease Control. Spina bifida and anencephaly before and after folic acid mandate – United States, 1995-1996 and 1999-2000. MMWR 2004;53(17):362-65.
  6. Peller AJ, Westgate MN, Holmes LB. Trends in congenital malformations, 1974-1999: effect of prenatal diagnosis and elective termination. Obstetrics & Gynecology 2004;104(5):957-64.