3.3 DAG
DAG (Figure S1) was plotted
according to our data analysis and previous
researches[18, 19]. As it showed, for the
relationship between PTB and exercise during pregnancy, the confounding
factors may include age, parity, occupation, and family income.
Pregnancy complications was a potential mediator, and it was not
adjusted in multivariate analysis[20].
3. 4
The effect of
exercise during pregnancy on PTB
Among women who did not exercise during pregnancy, the PTB rate was
5.37%. Among women who exercise during pregnancy, the PTB rate was
3.97%. Exercise during pregnancy was associated with 27% (OR =
0.73, 95% CI : 0.57-0.94) lower odds of PTB. After adjusting for
the covariates, exercise during pregnancy was associated with 26%
(OR = 0.74, 95% CI : 0.58-0.95) lower odds of PTB. For
time spent on exercise per week, the moderate group (2.5-7h/week) was
less likely to have PTB, the adjusted OR (95%CI ) was 0.72
(0.55-0.94). For energy expenditure per week, the moderate group
(11.25-31.5 MET.h/week) was less likely to have PTB, the adjustedOR (95%CI ) was 0.75 (0.58-0.96) (Table 2).
For each trimester (Figure 1), according to the time spent on exercise,
using the none and low group (0-2.4h/week) as a reference, different
trimesters had different results.
During the 1st trimester, the
moderate group (2.5-7h/week) was less likely to have PTB, the adjustedOR (95%CI ) was 0.77 (0.59-0.99). During the 2nd
trimester, the moderate group was less likely to have PTB,
the adjusted OR s
(95%CI ) were 0.74 (0.57-0.96). During the 3rd trimester, the
moderate group and the high group (>7h/week) were less
likely to have PTB, the adjusted OR s (95%CI ) were 0.74
(0.56-0.96) and 0.65 (0.44-0.94). According to the energy expenditure
(supplementary Table 2), during the 3rd trimester, the moderate group
(>7h/week) was less likely to have PTB, the adjustedOR s (95%CI ) were 0.74 (0.57-0.95). More details were
provided in supplementary material Table S2 and Table S3.