Longitudinal reference ranges for estimated fetal weight.
OBJECTIVE
The aims of the present study were to establish reference ranges for the growth of estimated fetal weight (EFW) between gestational weeks 20 and 42 and to determine the effect of fetal and maternal factors.


METHODS
This prospective longitudinal study was based on 634 low-risk pregnancies and a total of 1799 examinations. Gestational age was computed from last menstrual period. Head circumference, abdominal circumference, and femur length were measured using ultrasound, and EFW was calculated using the formula of Combs et al. The statistical analysis was based on regression analysis and multilevel modeling.


RESULTS
Intrauterine growth expressed by EFW showed a continuous pattern until term. Males were calculated to be 5% heavier than female fetuses at 20 gestational weeks and 3% at 40 weeks. Otherwise, the fetal and maternal effects on intrauterine growth correspond to a weight shift of 1.3% for breech/nonbreech, 2.5% for each increase in maternal height tertile, and -4% for smoking/nonsmoking. Maternal age higher than 34 years had a significant increased EFW of 4.5% compared with maternal age less than 24 years. Cephalic index in the third tertile had a 1.1% lower EFW compared with the first tertile. Maternal weight, body mass index, and parity did not influence the EFW. Terms for customization to individualize the growth patterns are presented.


CONCLUSIONS
The present growth chart is recommended as robust reference ranges for assessing EFW and growth. Fetal and maternal variables can be added into the models to individualize the prediction of EFW.
Johnsen
Synnøve Lian
SL
Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway. synnove.johnsen@helse-bergen.no
Rasmussen
Svein
S
Wilsgaard
Tom
T
Sollien
Rita
R
Kiserud
Torvid
T
D000328:Adult; D001724:Birth Weight; D005260:Female; D047109:Fetal Development; D005544:Forecasting; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008423:Maternal Age; D008962:Models, Theoretical; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012016:Reference Values; D012907:Smoking