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.