Table 1.
Characteristics of studies included in the systematic review and meta-analysis.
| Study: first author (year) [ref] | Country | Country income statusa | Cohort study design | Recruitment period | Number of women analysed | Population characteristics | Method to correct for confounders | Method to estimate gestational age | Quality assessment |
| Adam (2016) [20] | Sudan | Middle income | Retrospective | January 2009 to December 2013 | 78 | Women recruited from maternity hospital, urban and rural setting | Risk factor analysis | Unspecified | Average |
| Bailey (2013) [21] | Ukraine | Middle income | Retrospective | 2008 to 2010 | 3535 | First born twin included, all hospital deliveries, 14.7% history of IDU | None | LNMP and ultrasound (unspecified) | Poor |
| Bengtson (2020) [22] | South Africa | Middle income | Prospective | March 2013 to August 2015 | 1116 | Twins excluded, women recruited from antenatal care clinics in Gugulethu Cape Town, urban setting, 17.2% alcohol use | None | Ultrasound (unspecified), LMP or fundal height | Poor |
| Chen (2012) [23] | Botswana | Middle income | Retrospective | 1 May 2009 to 30 April 2011 | 33 148 | First born twin included, all hospital deliveries, 5.3% alcohol use, 1.7% smoking | Regression analysis, risk factor analysis | LNMP, SFH or ultrasound (unspecified) | Average |
| Dadabhai (2019) [24] | Malawi | Low income | Prospective | January 2016 to September 2017 | 1299 | Twins excluded, 96% of deliveries occurred in healthcare facilities, urban setting | Regression analysis | Ballard score and LMP | Average |
| Djeha (2019) [25] | Canada | High income | Prospective | January 2003 to December 2016 | 159 | Urban setting, 9.4% smoking | None | First trimester ultrasound or LMP | Average |
| Ekouevi (2008) [26] | Cote d’Ivoire | Low income | Prospective | March 2001 to July 2003 and August 2003 to August 2007 | 358 | Twins excluded, recruited from antenatal clinics, urban setting | Regression analysis | Unspecified | Average |
| Goetghebuer (2019) [27] | Belgium | High income | Prospective | December 2010 to November 2013 | 255 | Women recruited from hospital antenatal clinic, urban setting, 9.2% smoking, 10.1% alcohol | Risk factor analysis | Ballard score | Average |
| Hu (2019) [28] | China | Middle income | Prospective | October 2009 to May 2018 | 585 | Twins excluded, recruited through integrated prevention of MTCT programme, urban setting | Regression, risk factor analysis | First or second trimester ultrasound, if unable to assess ultrasound LMP used | Average |
| Kowalska (2003) [29] | Poland | Middle income | Prospective | January 1995 to February 2003 | 102 | Twins included, recruited from an outpatient HIV clinic, 47.1% IDU | Risk factor analysis | Unspecified | Poor |
| Li (2016) [30] | Tanzania | Low income | Prospective | November 2004 to September 2011 | 3314 | Recruited from hospitals, health centres and dispensaries, urban setting | Risk factor analysis | LNMP and SFH | Poor |
| Li (2020) [31] | China | Middle income | Prospective | October 2014 to September 2017 | 1449 | Twins excluded, women enrolled from midwifery hospitals | Regression, risk factor analysis | LMP or ultrasound (unspecified) | Average |
| Malaba (2017) [32] | South Africa | Middle income | Prospective | April 2013 to August 2015 | 1793 | Twins excluded, large community-based public sector primary care facility | Regression, risk factor analysis | LNMP and SFH | Average |
| Malaba (2021) [33] | South Africa | Middle income | Prospective | April 2015 to October 2016 | 3952 | Twins excluded, enrolled at first antenatal clinic in Cape town | Regression analysis | LMP, SFH and/or ultrasound (unspecified) | Average |
| Marazzi (2011) [34] | Malawi and Mozambique | Low income | Retrospective | July 2005 to June 2009 | 3273 | Twins included, women recruited from DREAM centres | Regression analysis | LNMP and clinical exam (unspecified) | Average |
| Moodley (2016) [35] | South Africa | Middle income | Retrospective | July 2011 to December 2011 and January 2014 to June 2014 | 9847 | Twins excluded, data abstracted from maternity registers of a regional hospital in Durban, South Africa | Regression analysis, risk factor analysis | LNMP and/or ultrasound (unspecified) | Average |
| Olagbuji (2010) [36] | Nigeria | Middle income | Prospective | January 2007 to December 2008 | 406 | Twins excluded, recruited from a tertiary referral centre, all women delivered in a healthcare facility | Risk factor analysis | Unspecified | Poor |
| Ramokolo (2017) [37] | South Africa | Middle income | Retrospective | October 2012 to May 2013 | 8778 | Twins excluded, recruited from primary health facilities | Risk factor analysis | LNMP | Average |
| Rempis (2017) [38] | Uganda | Low income | Retrospective | February 2013 to December 2013 | 412 | Twins excluded, all delivered in a private referral hospital | Risk factor analysis | Unspecified | Poor |
| Rubin (2011) [39] | Switzerland | High income | Prospective | 1984 to 2007 | 1040 | Twins excluded, 22% smoking, 26% IDU | None | Unspecified | Poor |
| Santosa (2019) [40] | South Africa | Middle income | Prospective | 28 May 2013 to 20 July 2016 | 633 | Twins excluded, women recruited from hospital in urban setting, 98.7% hospital deliveries, 6.4% smoking, 8.2% alcohol | Regression, risk factor analysis | Ultrasound <14 weeks | Good |
| Saums (2019) [41] | USA | High income | Retrospective | 2011 to 2018 | 3729 | Women recruited from hospital, urban setting, all hospital deliveries, 11.5% smoking, 2.9% alcohol, 13.4% IDU | Risk factor analysis | Unspecified | Average |
| Sebitloane (2017) [42] | South Africa | Middle income | Retrospective | 1 April 2011 to 30 April 2014 | 1461 | Twins excluded, women recruited and delivered at a regional hospital, urban setting | None | Unspecified | Poor |
| Short (2014) [43] | United Kingdom | High income | Retrospective | 1996 to 2010 | 331 | Twins included, 13.0% smoking, recruited from an HIV antenatal clinic, all women delivered in a tertiary hospital, urban setting | None | Unspecified | Poor |
| Silverman (2010) [44] | Zambia | Low income | Retrospective | Unspecified | 1238 | Twins included | Risk factor analysis | Unspecified | Poor |
| Snijdewind (2018) [45] | Netherlands | High income | Retrospective | January 1997 to February 2015 | 10 795 | Twins excluded, women recruited from 26 nationwide sites, 10.8% smoking, 11.7% alcohol use, 0.6% IDU, | Regression, risk factor analysis | LNMP and/or ultrasound (unspecified) | Average |
| Tan (2023) [46] | China | Middle income | Retrospective | January 2004 to December 2021 | 1010 | Twins excluded | Regression analysis | Unspecified | Average |
| Tiam (2019) [47] | Lesotho | Middle income | Prospective | June 2014 to February 2016 | 1594 | 91.6% delivered in a health facility, enrolment in 14 mixed setting study centres across 3 districts | None | LMP | Poor |
| Yu (2012) [48] | China | Middle income | Retrospective | June 2006 to July 2010 | 194 | Twins excluded, 8.8% IDU | Risk factor analysis | Unspecified | Poor |
| Zash (2017) [49] | Botswana | Middle income | Retrospective | 15 August 2014 to 15 August 2016 | 46 267 | Twins excluded, 6.3% alcohol consumption or smoking, obstetric records extracted at 8 national government hospitals | Regression analysis | LNMP and/or ultrasound (unspecified) or fundal height | Average |
| Zash (2018) [50] | Botswana | Middle income | Retrospective | 15 August 2014 to 15 August 2016 | 57 005 | Twins excluded, women recruited from 8 government hospitals, all hospital deliveries, 8.3% alcohol or smoking in pregnancy | Regression analysis | LNMP | Average |
Details on the inclusion of twins, recruitment centre, urban/rural setting, deliveries at home/hospital, smoking, alcohol use, and IDU were sought and reported here if provided by each study. IDU, illicit drug use; LMP, last menstrual period; LNMP, last normal menstrual period; MTCT, mother-to-child transmission; SFH, symphysio-fundal height.
a
Based on the World Bank country income classification at the time of the study.