Early pregnancy body mass index and spontaneous preterm birth in Northwest Russia: a registry-based study

Table 2 Associations between body mass index, preterm, moderate preterm and very preterm birth among 29,709 women with spontaneous singleton births

Response variables	n	% (95% CI)	Crude OR (95% CI)	p	Adjusted OR (95% CI)^‡	p	Adjusted OR (95% CI)^§	p
Preterm birth	1,645	5.5 (5.3-5.8)
Underweight	138	6.6 (5.6-7.7)	1.28 (1.06-1.54)	0.009	1.26 (1.04-1.51)	0.017	1.25 (1.03-1.50)	0.021
Normal	1,048	5.2 (4.9-5.5)	1	-	1	-	1	-
Overweight	314	5.8 (5.2-6.4)	1.12 (0.98-1.27)	0.099	1.09 (0.95-1.24)	0.215	1.10 (0.97-1.26)	0.152
Obese	145	6.9 (5.9-8.1)	1.35 (1.13-1.61)	0.001	1.29 (1.08-1.56)	0.006	1.31 (1.08-1.57)	0.005
Very preterm birth ^*	234	0.8 (0.7-0.9)
Underweight	19	0.9 (0.6-1.4)	1.30 (0.80-2.10)	0.285	1.30 (0.80-2.11)	0.292	1.26 (0.77-2.04)	0.356
Normal	140	0.7 (0.6-0.8)	1	-	1	-	1	-
Overweight	53	1.0 (0.8-1.3)	1.41 (1.02-1.93)	0.036	1.39 (1.01-1.92)	0.045	1.47 (1.06-2.03)	0.021
Obese	22	1.0 (0.7-1.6)	1.51 (0.96-2.37)	0.075	1.49 (0.94-2.37)	0.091	1.63 (1.02-2.60)	0.039
Moderate preterm birth ^†	1,411	4.8 (4.6-5.0)
Underweight	119	5.7 (4.8-6.8)	1.27 (1.04-1.55)	0.017	1.24 (1.02-1.52)	0.032	1.24 (1.02-1.51)	0.035
Normal	908	4.6 (4.3-4.9)	1	-	1	-	1	-
Overweight	261	4.9 (4.3-5.5)	1.07 (0.93-1.23)	0.347	1.04 (0.90-1.20)	0.591	1.05 (0.91-1.21)	0.524
Obese	123	5.9 (5.0-7.0)	1.32 (1.09-1.60)	0.005	1.26 (1.03-1.54)	0.022	1.26 (1.03-1.54)	0.026

^*Compared to moderate preterm and term births.
^†compared to term births (total n = 29,475).
^‡Adjusted for marital status, education, place of residence, mothers’ age, ethnicity, parity, smoking before pregnancy, alcohol abuse during pregnancy, and infant sex.
^§Adjusted for all above-mentioned variables and for diabetes mellitus 1 and 2 types and gestational diabetes, hyperemesis gravidarum, preeclampsia/eclampsia and excessive weight gain during pregnancy (O26.0 according to ICD 10).