Assessing first trimester growth: the influence of ethnic background and maternal age.

BACKGROUND: First trimester growth restriction may predict miscarriage or adverse outcome later in the pregnancy, but determinants of early growth are not well described. Our objective was to examine factors influencing fetal and gestational sac size in the first trimester. METHODS: Prospective observational study of 1828 singleton pregnancies before 12 weeks gestation. Maternal characteristics (ethnicity, maternal age, obstetric history, abdominal pain and vaginal bleeding), crown rump length (CRL) and mean gestational sac diameter (MSD) were recorded. A stepwise linear mixed effects analysis was performed to determine factors influencing rate of change in CRL and MSD. RESULTS: 1063 scans, in 464 women, were included. Rate of increase in CRL was higher in women of black ethnic origin (P = 0.0261) compared with white, and increased with advancing maternal age (P = 0.0046). Maternal age also influenced MSD: older women had gestational sacs which were 0.118 mm larger for each one year increase in maternal age (P = 0.0073). Bleeding, pain and prior obstetric history did not influence CRL or MSD. CONCLUSIONS: Rate of increase in CRL was greater in fetuses of black versus white women and increased with advancing maternal age. As CRL is used to date pregnancies, and this influences further growth assessment, consideration should be given to the use of individualized growth charts which take account of maternal factors found to influence first trimester growth.