生產前的葉酸會影響神經管缺陷發生率


  January 11, 2008 — 根據1月11日的每週死亡率與發病率報告中所登載的調查結果,生產前攝取葉酸與嬰兒的神經管缺陷發生率有關。
  
  疾病控制和預防中心的L. Alvelo-Maldonado醫師和同事表示,出生時的缺損是美國和波多黎各嬰兒死亡率的主要原因,神經管缺損(NTDs)是嚴重的脊椎與腦部出生缺損;最常見的兩種NTD是脊柱分裂和無腦症,在懷孕前和懷孕早期攝取葉酸可以預防NTD。
  
  美國NTD的流行病學,西班牙後裔者高於非西班牙後裔白人或者非西班牙後裔黑人婦女;美國的NTD發生率低於大多是西班牙裔居民的波多黎各,該國的發生率為每10,000新生兒有 8.68 人。
  
  研究者使用1996至2005年間的出生缺陷監控系統(BDSS)和1997至2006年間的行為風險因素監控系統(BRFSS)的資料,分析波多黎各的NTD發生率傾向和攝取葉酸知識之間的關係。
  
  生育年齡婦女知道攝取葉酸知識的百分比從1997到2003年是增加的,但是從2003到2006年是下降;相對的,NTD發生率從1996到2003年是下降的,2003到2005年則是維持穩定。
  
  作者指出,為了繼續降低NTD發生率,需要其他方式來增加波多黎各生育年齡婦女攝取葉酸的比率。
  
  BDSS是一項族群基礎的主動監控系統,每年評估將近50,000位於波多黎各出生者,BRFSS是一項持續進行的隨機撥號電話調查,對象是非收容機構中的18歲以上公民,7年的調查期間,共調查了6356位婦女。
  
  攝取葉酸的定義為每日攝取含有葉酸的維他命藥丸或補充品,知道葉酸相關知識的定義,是由健康照護人員建議攝取葉酸以預防出生缺陷;波多黎各每年發生的NTD從1996年的93 (每10,000活產14.7)降到2003年的27 (每10,000活產5.3) (P < .05),2004年為40 [每10,000活產7.8] ,2005年為44 [每10,000活產8.7]。
  
  這段期間,18-44歲的未懷孕婦女,攝取葉酸的比率從1997年的20.2%增加到2003年的30.9%,之後在2006年增加到24.8%;而知道葉酸相關知識的比率則是從1997年的22.4%增加到2003年的72.0%,以及在2006年降為56.5%。
  
  2006年時,教育程度越高以及家庭收入越高的婦女,比較可能具有葉酸相關知識和每日攝取葉酸補充品。
  
  一篇伴隨而來的編輯評論指出,波多黎各近幾年來,NTD缺損的結果(例如脊柱分裂和無腦症)已經引起關注;1996至2003年間的發生率降低是因為有婦女攝取葉酸的宣導活動,以及於1998年從美國引進含有葉酸的榖類製品;1997至2003年這段期間,波多黎各婦女攝取葉酸以及知道相關知識的比率是增加的,而在2003至2006年間則是下降。
  
  這些研究發現的限制是,BRFSS調查對象僅僅包括非收容機構且有一般有線電話的人,BRFSS有關葉酸攝取的問題並未明確說明每日建議劑量,僅提及維他命補充品,可能無法代表所有的NTD,其發生率低,也可能受到不同監控方法的影響。
  
  編輯指出,葉酸宣導活動在波多黎各繼續進行中,倡導健康事務以及其他教育議題;不過,儘管有這些方法,波多黎各僅約有四分之一的生育年齡婦女每天攝取含有葉酸的維他命,因此需要其他方式來改善;需要有其他方法了解這些因素,並且提高對葉酸的警覺性,同時建議波多黎各所有生育年齡的非懷孕婦女攝取葉酸。
  
  一篇QuickStats文章描述美國於1991、1995、2000和2005年的脊柱分裂和無腦症比率;1992年開始,美國國家健康促進機構明令生育年齡婦女每天攝取400 μg葉酸,以減少懷孕後造成NTD的風險。
  
  脊柱分裂比率從1995至2000年間的每活產25%,降到2000至2005年間的13%;無腦症比率從1991至1995年減少36%,1995至2005年間則無顯著改變。

Knowing Importance of Prenatal

By Laurie Barclay, MD
Medscape Medical News

January 11, 2008 — Knowledge of the importance of taking folic acid prenatally may be linked to incidence of infant neural tube defects, according to the results of a survey reported in the January 11 issue of the Morbidity and Mortality Weekly Report.

"Birth defects are one of the leading causes of infant mortality in both the mainland United States and Puerto Rico," write L. Alvelo-Maldonado, MS, and colleagues from the Centers for Disease Control and Prevention, Atlanta, Georgia. "Neural tube defects (NTDs) are serious birth defects of the spine and brain; two of the most common NTDs are spina bifida and anencephaly.... Consumption of folic acid before and during early pregnancy can prevent NTDs."

NTD prevalence in the United States is higher in Hispanic than in non-Hispanic white or non-Hispanic black women. NTD prevalence in the United States is lower than in Puerto Rico, where most residents are Hispanic, and where prevalence is 8.68 per 10,000 live births.

Using data from the Birth Defects Surveillance System (BDSS) for 1996 to 2005 and the Behavioral Risk Factor Surveillance System (BRFSS) for 1997 to 2006, the investigators analyzed trends in prevalence of NTD and in knowledge and consumption of folic acid supplements in Puerto Rico.

Prevalence among women of childbearing age of knowledge and consumption of folic acid increased from 1997 to 2003 but declined from 2003 to 2006. Correspondingly, NTD prevalence decreased from 1996 to 2003 but remained stable from 2003 to 2005.

"To resume the decline in prevalence of NTDs, additional measures might be needed to increase folic acid supplement use among Puerto Rican women of childbearing age," the authors write.

BDSS is a population-based, active surveillance system evaluating approximately 50,000 births in Puerto Rico annually, and BRFSS is an ongoing, random-digit-dialed telephone survey of the noninstitutionalized civilian population aged 18 years and older. During 7 years of surveys, 6356 women were surveyed.

Folic acid consumption was defined as reported daily intake of a vitamin pill or supplement containing folic acid, and knowledge regarding folic acid was defined as knowing that folic acid consumption is recommended by certain health experts to prevent birth defects.

In Puerto Rico, the annual number and prevalence of NTDs decreased from 93 (14.7 per 10,000 live births) in 1996 to 27 (5.3 per 10,000) in 2003 (P < .05) but then remained stable in 2004 (40 [7.8 per 10,000]) and 2005 (44 [8.7 per 10,000]).

During a comparable time frame, the estimated prevalence of folic acid consumption in nonpregnant women 18 to 44 years of age increased significantly from 20.2% in 1997 to 30.9% in 2003, then decreased to 24.8% in 2006. Correspondingly, the estimated prevalence of knowledge of folic acid increased from 22.4% in 1997 to 72.0% in 2003 but then declined to 56.5% in 2006.

In 2006, women with more education and those with highest household incomes were more likely to have knowledge regarding folic acid and to consume a folic acid supplement daily.

"The end of the decline in NTD (i.e., spina bifida and anencephaly) prevalence in Puerto Rico in recent years is a cause for concern," an accompanying editorial notes. "The decline from 1996 to 2003 likely was aided by a campaign urging women to consume folic acid supplements and by introduction of mandatory folic acid fortification of U.S. cereal grain products in 1998. During a similar period, 1997–2003, reported folic acid supplement consumption and knowledge about folic acid increased among women in Puerto Rico, before declining from 2003 to 2006."

Limitations of these findings are that BRFSS survey participants include only noninstitutionalized persons with landline telephones, BRFSS questions regarding folic acid consumption do not specify the recommended daily dose and pertain only to vitamin supplements, possible failure to document all NTDs, and prevalence of NTDs, which are rare, might be affected by even slight variations in surveillance methods.

"The folic acid campaign in Puerto Rico continues," the editorialist writes, noting health fairs and other educational campaigns. "However, despite these measures, only approximately one fourth of women of childbearing age in Puerto Rico consume a vitamin containing folic acid daily, suggesting that other factors might affect behavior. Additional measures directed at understanding these factors and promoting folic acid awareness and consumption among all nonpregnant Puerto Rican women of childbearing age are warranted."

An accompanying QuickStats article describes rates of anencephaly and spina bifida in the United States in 1991, 1995, 2000, and 2005. Beginning in 1992, a US national health recommendation has mandated that women of childbearing age consume 400 µg of folic acid daily to decrease the risk of NTD should they become pregnant.

Decrease in the rate of spina bifida per 100,000 live births was 25% from 1995 to 2000 and 13% from 2000 to 2005. Although the rate of anencephaly decreased 36% from 1991 to 1995, it did not change significantly from 1995 to 2005.

MMWR Morb Mortal Wkly Rep. 2008;57(1):10–13, 15.

    
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