Table 2 Univariate random-effects meta-regression analysis for heterogeneity by various covariates

Lactation volume

 Year of publication

 − 0.1454

0.0772

 − 0.2966

0.0059

 − 1.88

0.0597

 Sample size

0.0022

0.0021

 − 0.0020

0.0064

1.04

0.2993

 Duration

0.0005

0.0004

 − 0.0003

0.0013

1.30

0.1945

 Risk of bias

2.1123

1.0310

0.0915

4.1331

2.05

0.0405

Prolactin level

 Year of publication

0.1573

0.1629

 − 0.1620

0.4767

0.97

0.3341

 Sample size

 − 0.0228

0.0170

 − 0.0562

0.0105

 − 1.34

0.1795

 Duration

0.0016

0.0035

 − 0.0052

0.0083

0.45

0.6511

 Risk of bias

 − 1.4109

1.7830

 − 4.9055

2.0838

 − 0.79

0.4288