Discussion
The association of pre-pregnancy BMI with adverse pregnancy outcomes is
not fully understand, especially in low-income and middle-income
countries, where levels of maternal overweight/obesity is increasing and
underweight is still high.14 In this large cohort
study conducted in China, we found that compared with women with normal
weight, pre-pregnancy underweight was positively associated with risk of
PTB and SGA but inversely associated with risk of LGA, primary caesarean
delivery and stillbirth; overweight was positively associated with risk
of LGA, primary caesarean delivery and stillbirth but inversely
associated with risk of SGA and shoulder dystocia or birth injury; and
obesity was positively associated with risk of PTB, LGA and primary
caesarean delivery but inversely associated with risk of SGA. However,
these associations differ according to maternal age.