TABLE 1.
Characteristics and quality assessment of included studies
| Author | Year | Country | Study design | Number of participants | Gestational week at examination | Ultrasound characteristics | Reported outcomes | NOS score |
|---|---|---|---|---|---|---|---|---|
| Hata | 1995 | Japan | Case control | 27 | >32 | Patients were studied once with color Doppler flow imaging and pulsed Doppler ultrasonography after 32 weeks gestation. | PSV, MV, EDV, PI | 7 |
| Takata | 2002 | Japan | Case control | 84 | >32 | An Aloka SSD‐2200 scanner with a 3.5‐MHz transabdominal probe (Aloka Ltd., Tokyo, Japan) was used. | PSV, MV, EDV, PI, RI, PR | 8 |
| Ayaz | 2003 | Turkey | Case control | 60 | >32 | Ultrasound examination was performed using a 10 MHz linear transducer. | PI and RI | 8 |
| de Oliveira | 2013 | Brazil | cross‐sectional | 349 | >20 | All scans were performed using Nemio (Toshiba Medical Systems Co, Ltd, Tokyo, Japan) and Sonoace X8 (Samsung Medison Co, Ltd, Seoul, Korea) high‐resolution equipment with a 7.5‐MHz linear transducer and a 50 Hz wall filter setting; the Doppler sample volume was adjusted at 2 to 3 mm. | RI, PI, PR | 8 |
| Diniz | 2008 | Brazil | Cross‐sectional | 91 | 30.7 ± 5.0 | Orbital vascular Doppler was performed using an electronic linear probe in a frequency ranging from 7–10 MHz. | PSV, EDV, PI, RI, PR | 7 |
| Olatunji | 2015 | Nigeria | Case control | 82 | NR | Transorbital triplex ultrasound scan with a 7–10 MHz multifrequency linear transducer was used. | PSV, PI EDV, RI | 8 |
| Madina | 2020 | Pakistan | Cross‐sectional | 60 | Second or third trimester. | The ultrasound machine used in the study (Toshiba Xerio) was equipped with a linear probe of 7–14 MHz for ophthalmic artery examination. | RI | 8 |
| Onwudiegwu | 2020 | Nigeria | Case control | 143 | NR | Ocular color and pulsed‐wave Doppler ultrasound examination of the ophthalmic artery was done on all participants using the LOQIC P5 GE ultrasound scanner (General Electric Healthcare, South Korea) with a 5–14 MHz linear transducer. | PI, RI, PSV, PR, EDV | 7 |
Abbreviations: EDV, end‐diastolic velocities; MV, time‐averaged mean peak velocities; NOS, Newcastle‐Ottawa Scale; NR, not reported; PI, pulsatility index; PR, peak ratio; PSV, peak systolic velocities; RI, resistance index.