First-trimester crown-rump length affects birth size symmetrically

To investigate the relationship between crown-rump length (CRL) and birth weight, length and head circumference of the newborn.

From a database of delivery records of 12,000 pregnancies, we identified 999 women with singleton pregnancies who had no medical problems, a normal menstrual history and a first trimester ultrasound scan in which CRL had been measured. All of the pregnancies resulted in live births without evidence of chromosomal and congenital abnormalities. The population in this study was divided into three groups according to CRL measurement; Group A (smaller-than-expected CRL), Group B (normal CRL) and Group C (larger-than-expected CRL).

The incidence of low birth weight infant was higher in Group A than in Group C (p = 0.010). The rate of small for gestational age (SGA) infants was similar between groups. The number of macrosomic or large for gestational age (LGA) infants was higher in Group C than Groups A and B. Both birth head circumference and length of infant were greater in Group C than Groups A and B. No significant difference for ponderal index value was observed between the groups (p = 0.927).

The growth pattern in the first trimester affects neonatal birth weight and length symmetrically without changing the ponderal index.