Fig 1.
Flow diagram showing the composition of the final data used in this analysis.
Exclusions from the data are detailed in Fig 1. Births which took place before 24 weeks or after 42 weeks gestation were excluded as SGA reference values do not exist for these gestations. An exclusion for pregnancies where the first ANA for the second pregnancy took place after 168 days gestation (as assessed by ultrasound examination performed by healthcare professionals) was made since these were likely to be high-risk pregnancies referred from elsewhere. Variables documenting the previous numbers of live and stillbirths were used to identify women giving birth for the first and second time and to exclude women who either had a first or second birth elsewhere or who had a stillbirth prior to their first live birth or between live births.
Table 1.
Summary of derived smoking categories based on self-reported maternal smoking status recorded at the first antenatal appointment for each pregnancy.
Fig 2.
Directed acyclic graph showing the exposure (interpregnancy smoking change) and the outcome (being born small for gestational age (SGA)).
Table 2.
Maternal characteristics recorded at the first antenatal appointment at the start of the second pregnancy, together with characteristics of both the first and second infants.
Fig 3.
The percentages of small for gestational age births in the first and second pregnancies.
Table 3 shows the univariate odds of small for gestational age birth in the second pregnancy by maternal characteristics recorded at the start of each pregnancy.
Table 3.
Univariate odds of small for gestational age birth (< 10th percentile) in the second pregnancy in the full sample, by maternal characteristics recorded at the start of or during the first and second pregnancies.
Table 4.
The odds of small for gestational age birth (< 10th percentile) in the second pregnancy.
Table 5.
Full results of Model 1 in Table 4; the adjusted odds of small for gestational age birth (<10th percentile) in the second pregnancy in the full sample.