Table 3 Linear regression estimates for association between change in maternal body mass index (BMI) measured at the first antenatal visit of each pregnancy and the length of the interpregnancy interval (in years).

	First to second pregnancy			Second to third pregnancy			Third to fourth pregnancy			Fourth to fifth pregnancy
	n	Maternal BMI per year (99% CI)	p	n	Maternal BMI per year (99% CI)	p	n	Maternal BMI per year (99% CI)	p	n	Maternal BMI per year (99% CI)	p
Unadjusted	15940	0.27 0.23 to 0.30	<0.001	5738	0.22 0.17 to 0.27	<0.001	2165	0.24 0.16 to 0.32	<0.001	738	0.34 0.21 to 0.48	<0.001
Model 1	15940	0.27 0.24 to 0.31	<0.001	5738	0.22 0.18 to 0.27	<0.001	2165	0.25 0.17 to 0.33	<0.001	738	0.33 0.20 to 0.47	<0.001
Model 2	15259	0.25 0.21 to 0.28	<0.001	5498	0.24 0.19 to 0.29	<0.001	2081	0.25 0.16 to 0.33	<0.001	711	0.36 0.22 to 0.50	<0.001
Model 3	15259	0.25 0.21 to 0.28	<0.001	5498	0.24 0.19 to 0.29	<0.001	2081	0.25 0.16 to 0.33	<0.001	711	0.36 0.22 to 0.50	<0.001
Model 4	4667	0.17 0.07 to 0.26	<0.001	1608	0.19 0.04 to 0.33	0.001	617	0.07 −0.19 to 0.32	0.51	213	0.32 −0.06 to 0.71	0.03

Model 1 is adjusted for: timing of first (booking) antenatal appointments (as this is when maternal BMI is measured).
Model 2 is adjusted for: timing of first (booking) antenatal appointments, maternal age, ethnicity, highest educational qualification, whether undergone infertility treatment, smoking and employment status.
Model 3 is adjusted for: first (booking) antenatal appointment, maternal age, ethnicity, highest educational qualification, whether undergone infertility treatment, smoking, employment status and baseline maternal BMI (for the first pregnancy in the dataset).
Model 4 is adjusted for: first (booking) antenatal appointments, maternal age, ethnicity, highest educational qualification, whether undergone infertility treatment, smoking, employment status, baseline maternal BMI and breastfeeding or not at hospital discharge.

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