Associations of COVID-19 lockdown with gestational length and preterm birth in China

Table 4 Modification effects of infant sex on the associations of COVID-19 lockdown exposure with gestational length and PTB risk

	No. of participants				Gestational length (week, Mean ± SD)				Mean difference in gestational length (week) Adjusted β (95% CI) ^*		P for modification effects of infant sex
	Male		Female		Male		Female		Male	Female	P for modification effects of infant sex
	Unexposed group	Exposed group ^a	Unexposed group	Exposed group ^a	Unexposed group	Exposed group ^a	Unexposed group	Exposed group ^a
Gestational week during the Level I lockdown
All	263,153	54,349	230,343	47,551	38.66 ± 1.48	38.58 ± 1.48	38.82 ± 1.43	38.74 ± 1.44	−0.06 (−0.08, −0.05)	−0.06 (−0.08, −0.05)	> 0.05
	No. of participants				PTB rate (N, %)				PTB risk Adjusted OR (95%CI) ^*		P for modification effects of infant sex
	Male		Female		Male		Female		Male	Female	P for modification effects of infant sex
	Unexposed group	Exposed group ^a	Unexposed group	Exposed group ^a	Unexposed group	Exposed group ^a	Unexposed group	Exposed group ^a
Gestational week during the Level I lockdown
All	254,522	52,471	222,393	45,791	14,873 (5.8)	3269 (6.2)	10,758 (4.8)	2324 (5.1)	1.09 (1.04, 1.13)	1.08 (1.03, 1.13)	> 0.05

PTB preterm birth
^* Adjusted for maternal age, marital status, residential city, delivery type and parity
^a Pregnant women who have experienced the COVID-19 lockdown (from 1/23/2020 to 2/24/2020) during their any period of pregnancy were defined as the exposed group

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