Effects of Maternal Factors on Birth Weight in Japan
Table 3
Differences of birth weight between 2006 and 2010 before and after adjusting each confounding factor by ANCOVA.
Value
Difference
2006
2010
Difference of birth weight before adjustment by ANCOVA
Birth weight (g)
2950.840
2937.520
13.320
—
—
13.320
Estimation for net effect on birth weight of each factor by ANCOVA
Partial confounding factors
Net effect (g)
Total effect (g)
Gestational age at delivery (weeks)
39.087
38.985
0.102
160.081
16.360
11.156
Primiparity
0.530
0.544
−0.014
−104.796
1.496
Cesarean delivery
0.236
0.285
−0.050
−2.046
0.102
Weight gain during pregnancy (kg)
9.846
9.842
0.004
16.269
0.064
Female gender
0.489
0.487
0.002
−107.150
−0.236
Induction of labor
0.236
0.269
−0.033
9.714
−0.322
Pregestational BMI
21.057
21.092
−0.035
22.250
−0.774
IVF-ET
0.023
0.044
−0.021
37.404
−0.785
Smoking habit
0.053
0.044
0.009
−107.593
−0.954
Maternal height (cm)
158.338
158.471
−0.133
10.270
−1.366
Maternal age (year)
31.119
32.002
−0.883
2.752
−2.428
Difference of birth weight after adjustment by ANCOVA
Birth weight (g)
2.164
meant a partial regression coefficient. Net effect was calculated by product of difference and partial regression coefficient. Total effect was derived from sum of net effect. ANCOVA: analysis of covariance, BMI: body mass index, and IVF-ET: in vitro fertilization and endometrial transfer.
