Impact of maternal characteristics on fetal growth in the third trimester: a population-based study.

OBJECTIVES: To investigate the association between maternal characteristics and fetal growth during the third trimester of pregnancy.
METHODS: Using a population-based perinatal register, 48809 term singleton pregnancies were identified for which a routine ultrasound examination in the third trimester had been performed between 1995 and 2009. Fetal and infant weight were expressed as gestational age-specific standard deviation scores (z-scores) using a Swedish ultrasound-based reference curve. The growth of each fetus was assessed using the difference between the birth-weight z-score and the fetal-weight z-score estimated at the ultrasound examination, adjusted for gestational age, and divided by the time elapsed between the ultrasound examination and delivery. Analyses were performed using multivariable linear and polynomial regression analyses.
RESULTS: Positive associations were found between maternal body mass index (BMI), height, pre-existing diabetes mellitus, female fetal gender and fetal growth, whereas maternal smoking had a negative association. In the univariate analyses, primiparity and parity with four or more previous children were significantly associated with reduced fetal growth, but in the multivariable analysis, no association between parity and fetal growth could be detected. Both univariate and multivariable analyses revealed a significant inverse U-shaped association between maternal age and fetal growth.
CONCLUSIONS: Third-trimester fetal growth was positively associated with increasing maternal BMI, height and pre-existing diabetes mellitus, and negatively associated with maternal smoking.