Association of pre-pregnancy BMI with pregnancy outcomes
The characteristics of new-borns and frequencies of outcomes according
to pre-pregnancy BMI are shown in Table 1. Overall, the incidence ratios
of PTB, LGA, SGA, primary caesarean delivery, should dystocia or birth
injury, and stillbirths were 5.0%, 11.5%, 9.7%, 14.5%, 1.1% and
1.2‰ among the study population.
The adjusted RRs and 95% CIs of the six outcomes for pre-pregnancy BMI
are shown in Table 2. In the fully adjusted model (model 3), compared
with normal weight, underweight was inversely associated with risk of
LGA birth (adjusted RR 0.83, 95%CI 0.82-0.85), primary caesarean
delivery (0.88, 0.87-0.90) and stillbirth (0.73, 0.53-0.99), but
positively associated with risk of PTB (1.06, 1.04-1.09) and SGA (1.23,
1.22-1.26). Overweight was inversely associated with risk of SGA birth
(0.92, 0.90-0.95) and shoulder dystocia or birth injury (0.86,
0.79-0.93), but positively associated with risk of LGA (1.17,
1.14-1.19), primary caesarean delivery (1.18, 1.16-1.20) and stillbirth
(1.44, 1.03-2.06). Pre-pregnancy obesity was inversely associated with
risk of SGA birth (0.92, 0.87-0.97) but was positively associated with
risk of PTB (1.12, 1.05-1.20), LGA birth (1.32, 1.27-1.37), and primary
caesarean delivery (1.45, 1.40-1.50). In all the three models of the six
outcomes, the adjusted RRs did not substantially change.