Variables and Definitions of Terms
The outcome variable of interest was GBS colonization of pregnant
mothers during gestation. GBS colonization status was determined by
recto-vaginal swabs at 35-37 weeks gestation and consisted of placement
of the genital swab approximately 2 cm into the vagina followed by
placement through the anal sphincter. The result of the test was defined
as either positive or negative by the PCR using standard techniques as
described. 13 Tobacco smoking was defined by the
number of cigarettes smoked per day during gestation. This variable was
accurately recorded by the attending obstetrician during prenatal
visits. In the rare instances when this information was missing in the
EHR of the obstetrician, e.g. because of lack of prenatal care, the
pediatrician usually recorded the smoking status after delivery by
direct questioning of the new mother during her Nursery stay. If the
mother smoked during pregnancy, the number of cigarettes was also
recorded in the mother’s EHR by the obstetrician or the pediatrician.
Information on tobacco smoking status of all subjects was thus
available. Maternal variables abstracted were: age in years, parity,
history of gestational diabetes, race, and substance use. Infant factors
abstracted were: birthweight in grams, gestational age in weeks, and
gender of the newborn baby (male or female). Maternal substance use was
defined as any use during pregnancy of various drugs such as cocaine,
various opiates (e.g., methadone, OxyContin, buprenorphine (Subutex),
cannabinoids, or other illegal substances. These potential risk factors
were all gleaned from the literature.