THE LENGTH OF HUMAN-PREGNANCY AS CALCULATED BY ULTRASONOGRAPHIC MEASUREMENT OF THE FETAL BIPARIETAL DIAMETER

Pregnancy length was calculated from ultrasonic measurement of the fet al biparietal diameter (BPD) in the second trimester and compared with the corresponding length calculated from the last menstrual period (L MP) in 865 women with exactly 28-day cycles and spontaneous onset of l abor. The effects of maternal age, parity, smoking and sec of the chil d on BRD-based pregnancy length were evaluated in 1998 women with spon taneous onset of labor. The mean pregnancy length was 280.6 days when based on BPD and 283.6 days when based on LMP. The corresponding media n values were 281 days and 284 days, respectively. Probably because of more preterm deliveries, women below 20 years of age has a significan tly shorter pregnancy length than women 20-34 years of age. Women carr ying girls had a significantly shorter pregnancy length than women car rying boys. There was a tendency to shorter pregnancy lengths among mu ltiparae and among smokers.