Associations between prenatal alcohol and tobacco exposure on Doppler flow velocity waveforms in pregnancy: a South African study

Table 3 Independent variables included in the stepwise manual backward elimination (multi-level) GAM models for infant birth weight

	Covariates	GAM 3	GAM 4
Child	Gestational age at delivery in days	P < 0.001	P < 0.001
	Gender	P < 0.05	P < 0.01
Doppler	Uterine artery pulsatility index trimester 2
	Umbilical artery pulsatility index trimester 2
	Middle cerebral artery pulsatility index trimester 2
	Uterine artery pulsatility index trimester 3
	Umbilical artery pulsatility index trimester 3		P < 0.001
	Middle cerebral artery pulsatility index trimester 3	P < 0.01	P < 0.05
Exposure	Cigarettes per day trimester 1	P < 0.01	P < 0.05
	Cigarettes per day trimester 2
	Cigarettes per day trimester 3
	Total number of cigarettes smoked during pregnancy
	Total number of standard drinks consumed trimester 1
	Total number of standard drinks consumed trimester 2	P < 0.01	P < 0.05
	Total number of standard drinks consumed trimester 3
	Total number of standard drinks consumed during pregnancy
	Total number of binges during pregnancy
	Variance explained/GAM results	40.2	40.7
	R² adjusted	0.36	0.358

Note: A stepwise manual backward elimination process was run and the variables significant in the final model at each stage are indicated above

ISSN: 1471-2393