Table 2 Results of extrapolating early-pregnancy weights in Study I and interpolating early-pregnancy weights in Study II

Mixed-effects models

All weights included (n=6272)

Dropping third trimester weights (n=3375)

All weights included (n=11,775)

Dropping third trimester weights (n=8125)

 3 knots (quartiles)

1.99

2.01

1.69

1.64

 4 knots (quintiles)

2.08

2.05

1.66

1.59

 5 knots (sextiles)

2.18

N/A^a

1.60

1.70

 3 knots (5th, 50th, 95th)

2.00

2.00

1.67

1.63

 4 knots (5th, 35th, 65th, 95th)

2.00

1.98

1.62

1.66

 5 knots (5th, 27.5th, 50th, 72.5th, 95th)

2.25

1.98

1.60

1.81

 Linear

2.02

2.01

1.67

1.65

 Quadratic

2.02

1.95

1.66

1.62

 Cubic

2.02

6.46

1.62

N/A^a

Marginal models with GEE

Mean residual

Nearest weight residual

Mean residual

Nearest weight residual

 3 knots (quartiles)

2.94

3.94

2.03

1.98

 4 knots (quintiles)

2.94

3.94

2.00

1.97

 5 knots (sextiles)

2.94

3.94

1.96

1.96

 3 knots (5th, 50th, 95th)

2.94

3.94

2.02

1.97

 4 knots (5th, 35th, 65th, 95th)

2.94

3.93

1.97

1.96

 5 knots (5th, 27.5th, 50th, 72.5th, 95th)

2.94

3.92

1.95

2.01

 Linear

2.94

3.94

2.01

2.03

 Quadratic

2.94

3.94

2.02

1.98

 Cubic

2.93

3.92

1.97

1.96

Assigning the nearest weight measure

Arithmetic imputation using the nearest two weight measures