First author | Year | Country | Study design | Sample size | Period prevalence | Duration* | Birth outcome | Epidemiological study | Prevalence (%) |
Airede23 | 1992 | Nigeria | PS | 5977 | June 1987 -June 1990 | 36 | LB+SB | Incidence | 0.134 |
Adetiloye24 | 1993 | Nigeria | RS | 23 438 | 1982–1992 | 120 | LB+SB | Incidence | 0.051 |
Mukhtar-Yola25 | 2005 | Nigeria†⃰ | RS | 13 619 | October 1998-November 2004 | 72 | LB+SB | Prevalence | 0.059 |
Ugwu26 | 2007 | Nigeria⃰† | RS | 7388 | May 2002-April 2005 | 36 | LB+SB | Incidence | 0.081 |
Anyanwu27 | 2015 | Nigeria⃰† | PS | 1456 | April 2013-December 2013 | 9 | LB | Prevalence | 0.069 |
Nnadi28 | 2016 | Nigeria⃰† | PS | 10 163 | January 2011- December 2013 | 36 | LB+SB | Prevalence | 0.01 |
Abbey29 | 2017 | Nigeria⃰† | RS | 7670 | August 2011-December 2014 | 48 | LB‡ | Prevalence | 0.039 |
Ekwochi30 | 2018 | Nigeria⃰† | PS | 5830 | January 2013- January 2017 | 48 | LB | Incidence | 0.034 |
Buccimazza31 | 1994 | South Africa | RS | 516 252 | January 1973 -December 1992 | 240 | LB+SB | Prevalence | 0.008 |
Delport32 | 1995 | South Africa | PS | 17 351 | May 1986-April 1989 | 36 | LB | Incidence | 0.012 |
Venter33 | 1995 | South Africa | PS | 7617 | June 1989 -December 1992 | 40 | LB | Incidence | 0.026 |
Kinasha34 | 2003 | Tanzania | RS | 34 000 | January 2000 -January 2002 | 24 | LB | Incidence | 0.029 |
Kishimba35 | 2015 | Tanzania⃰† | CS | 28 217 | Octover 2011-February 2012 | 5 | LB+SB | Prevalence | 0.011 |
Muga36 | 2009 | Kenya | PS | 7355 | September 1983-September 1984 | 12 | LB+SB‡ | Incidence | 0.014 |
Agot37 | 2020 | Kenya⃰ | RS | 299 854 | January 2014 - Decemeber 2018 | 60 | LB | Prevalence | 0.0007 |
Elsheikh38 | 2009 | Sudan | PS | 18 378 | February 2003 -Jan 2004 | 12 | LB+SB | Incidence | 0.049 |
Omer39 | 2016 | Sudan⃰† | CS | 36 785 | August 2014 - July 2015 | 12 | LB+SB | Prevalence | 0.038 |
Gedefaw40 | 2018 | Ethiopia⃰† | PS | 8677 | February 2016-August 2016 | 7 | LB+SB§ | Incidence | 0.035 |
Abebe41 | 2020 | Ethiopia† | RS | 45 951 | September 2011-December 2015 | 60 | LB+SB | Prevalence | 0.009 |
Ahuka42 | 2006 | DR of Congo | RS | 8824 | January 1993 -August 2001 | 96 | LB | Incidence | 0.023 |
Houcher43 | 2008 | Algeria | RS | 28 500 | 2004–2006 | 36 | LB+SB§ | Prevalence case–control | 0.004 |
Njamnshi44 | 2008 | Cameron | RS | 52 710 | January 1997 -December 2006 | 120 | LB+SB | Incidence | 0.0095 |
Mohammed45 | 2011 | Egypt | CS | 5000 | March 2007- October 2007 | 7 | LB | Prevalence | 0.04 |
Nasri46 | 2014 | Tunisia | RS | 3 803 889 | 1991–2011 | 240 | LB+SB | Prevalence | 0.004 |
Radouani47 | 2015 | Morocco⃰† | RS | 60 017 | January 2008-December 2011 | 48 | LB+SB | Prevalence | 0.0017 |
Alhassan48 | 2017 | Ghana⃰† | RS | 35 426 | January 2010 - December 2014 | 48 | LB+SB | Prevalence | 0.0085 |
El-Moghrabi49 | 2019 | Libya | CS | 16 765 | September 2004-August 2005 | 12 | LB | Incidence | 0.006 |
*Duration per months.
†Mandatory and/or voluntary folic acid fortification policy.
‡Singleton births+twin births+multiple births.
§Singleton births+twin births.
CS, cross-sectional; LB, live births; PS, prospective; RS, retrospective; SB, stillbirths.