Open AccessNormal Range Curves for the Intrauterine Growth of the Biparietal Diameter
Author(s) -
Persson P.H.,
Grennert L.,
Gennser G.,
Gullberg B.
Publication year - 1978
Publication title -
acta obstetricia et gynecologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.401
H-Index - 102
eISSN - 1600-0412
pISSN - 0001-6349
DOI - 10.3109/00016347809162697
Subject(s) - medicine , biparietal diameter , confidence interval , hysterotomy , ultrasound , standard deviation , gestational age , pregnancy , growth curve (statistics) , percentile , nuclear medicine , fetus , obstetrics , mathematics , statistics , head circumference , genetics , radiology , biology
. Normal range curves for the growth of the fetal biparietal diameter (BPD) measured by ultrasound were calculated in three different ways; I. 93 selected women examined longitudinally with three‐week intervals from the 16th gestational week to term. II. Measurements for each week compiled with only the first measurement from each patient. From the 20th to the 30th week, 3,243 BPD determinations obtained in a routine screening programme was used. III. 157 BPD measurements from 60 women with known date of ovulation. The results revealed that the three growth curves obtained in different ways were almost identical. The daily BPD increase was 0.44 mm up to the 33rd week. Thereafter, the increment declined. The data were best explained by an equation of the third degree (98.9 %) for the whole investigated period (16‐40 weeks), and before the 33rd week, best fitted to a straight line. Reliability was assessed by the test‐retest method. The error introduced by the unreliability of measurements had a standard deviation of 0.9 mm. The mean difference between examinations performed with an interval of one day was equal to the BPD growth for one day: 0.44 mm. To assess accuracy, the ultrasonic BPD measurements were checked against caliper measurements of the fetal head, in the first half of pregnancy after hysterotomy, and at term after cesarean section. The mean difference was 0.44 mm and 1.3 mm, respectively (SD 1.5 and 1.3 mm). The variation of the normal curve obtained from longitudinal measurements was 3.4 mm (SD) and the variation of the curve obtained from patients with known date of ovulation was 2.2 mm (SD). By comparing the two curves (I and III), 52 % of the variance around the mean of the former curve could be explained by difference in gestational age; 11 % was due to lack of accuracy, 6 % to lack of reliability, and 31 % to individual difference.