Assessment of Perinatal Outcomes.
Gestational age was estimated based on first trimester ultrasound scan. Serial obstetric ultrasounds were performed bi-weekly in the third trimester to monitor fetal growth. Umbilical artery Doppler studies were performed in those with suspected intrauterine growth restriction (IUGR). Premature birth was defined as births that occurred before 37 weeks of gestation. Low birth weight (LBW) and very low birth weight (VLBW) were defined as birth weights below 2,500 and 1500 grams respectively. Fetal death was defined as a fetus weighing greater than 500g with no signs of life at birth and meeting all the following criteria; no fetal heartbeat; no respiratory effort; absence of pulsation in the umbilical cord; and no definitive movement of voluntary muscles.
Spirometry Evaluation.
A trained physician and a trained research technician performed spirometry for each participant at baseline visit (< 28 weeks of pregnancy) using the Morgan FVL spirometer according to the American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines16. The spirometry procedure was first demonstrated to each participant, after which the participant was made to perform the spirometry. Each participant was made to inhale rapidly and completely from functional residual capacity, after which the breathing tube was inserted into the participant’s mouth, with the lips sealed around the mouthpiece and the tongue not occluding the mouthpiece. The forced vital capacity (FVC) maneuver was then started with minimal hesitation (within 1–2 seconds after inspiring to the total lung capacity). The participant was prompted to “blast” the air from their lungs, and was then encouraged to fully exhale. Throughout the FVC maneuver, enthusiastic coaching of each participant was carry out using appropriate body language and phrases, such as “keep blowing” or “keep going”. Measured and calculated spirometric indices from the FVC maneuver included FEV1, FVC, and the ratio of FEV1 to FVC (FEV1/FVC). The predicted values of the FEV1, FVC, and the FEV1/FVC ratio were determined for each participant based on their age, gender, height, and ethnic group using the Global Lung Initiative 2012 equations 17. Poor lung function was defined as FEV1% predicted < 6518,19 . The choice of 0.65 as the threshold for FEV1% predicted is based on its predictive value for mortality in the general population 19.