This study was conducted at the postnatal ward of King Khalid University Hospital (KKUH) in the Kingdom of Saudi Arabia for the period of 12 months from the 1st of October 2011 to 30th of September 2012. KKUH is a tertiary referral center; includes a neonatal intensive care unit (NICU) and in vitro fertilization unit. The obstetrics department provides services for 3500–4000 deliveries per year.
The study was designed to investigate the independent effects of maternal BMI and maternal exposure to SHS on the new-borns’ anthropometric measurements (birth weight, length, and head circumference), LBW < 2.5 kg and macrosomia (≥4.0 kg) in term infants.
Consecutive women who consented to join the study and met the inclusion criteria were enrolled. The inclusion criteria were:
Women with singleton pregnancy.
Term delivery (≥ 37 gestational weeks counted from the last menstrual period and/or early ultra-sound scan).
Women who did not smoke during the index pregnancy and were exposed to SHS.
Women who did not smoke during the index pregnancy and were not exposed to SHS.
We excluded from this study women with unknown smoking status and those who did not have recorded weight and/or height at time of booking to the antenatal clinic.
Data were collected using a predesigned data collection sheet from women in the postnatal ward within 24–48 hours following delivery, by nurses and researchers who were trained to collect the data. Demographic characteristics and pregnancy outcomes data were extracted from the medical records, while tobacco use data were obtained by interview. The researchers who conducted the interviews were not aware of the data extracted from the medical records.
Women who met the inclusion criteria and consented to the study were asked about their exposure to SHS, which was defined as occurring when a woman, who did not smoke at all whilst pregnant, lived with a household member (husband, son, daughter or other relatives) who was reported to smoke during the index pregnancy. We did not assess occupational exposure. Duration of exposure to SHS was not reported in this study as only 30% of the participants could recall the duration of exposure.
Women were booked for their first antenatal visit during the first or the second trimester of pregnancy, subject to availability of appointments.
The data collected from the antenatal records included; maternal age, parity, maternal height and weight recorded during the first antenatal visit, from which, BMI was calculated according to the following equation; BMI = weight (kg)/height (m)2, in addition to any antenatal events including the occurrence of preeclampsia and pre-existed or gestational diabetes (GDM) as per antenatal record diagnosis. These variables were extracted and analysed as confounders due to their known influence on newborn anthropometry.
Data of the newborn included gestational age at delivery, weight, length and head circumference.
To investigate the independent effects of maternal obesity and exposure to SHS on the newborn’s anthropometric measurements, women were stratified into three groups based on the BMI; underweight (BMI <18 kg/m2) non-obese (BMI 18–29.99 kg/m2) and obese (BMI ≥ 30 kg/m2). Further stratification of the study population into a total of six groups was based on the results of the SHS exposure; where non- obese women who reported non-exposure to SHS were considered the control group. We compared the birth weight, length and head circumference, of infants of mothers who were exposed to SHS to those of mothers who were exposed, stratified according to the BMI. In addition we estimated the risk of delivering a macrosomic or an LBW baby by calculating the odds ratio (OR) for each category of women.
Data were analysed using Statistical Package for the Social Sciences (SPSS), Version 20 (SPSS Inc., Chicago, IL, USA). We compared means using either the Student’s t test or analysis of variance (ANOVA) for continuous variables, as appropriate, and Pearson's chi-squared test for categorical variables; non-parametric tests were used as appropriate. Univariate analysis was performed to compare the anthropometric measurements of infants of women who were exposed to SHS to those of women who were not exposed and to evaluate the associations between maternal BMI and exposure to SHS with anthropometric measurements.
Stepwise multiple logistic regression analysis was used to explore the independent associations between the six groups regarding the risk of delivering a macrosomic or an LBW infant, considering non-obese women who reported non-exposure to SHS as the reference group. Adjusted ORs were calculated and the following variables were adjusted for in the regression model; maternal age, parity, gestation age 37–42 weeks, GDM, preeclampsia and pre-existing diabetes mellitus. P value of < 0.05 was considered significant.
Ethical approval was sought and granted before commencing the study from the institutional review board of College of Medicine King Saud University.