Amniotic fluid volume in normal singleton pregnancies: modeling with quantile regression.
OBJECTIVE
To develop uniform and reliable reference ranges for amniotic fluid volume (AFV) across gestation in normal singleton pregnancies using quantile regression (QR).


METHODS
An analysis of true AFVs determined by dye-dilution techniques or by direct measurement at cesarean delivery in normal singleton pregnancies. AFV centiles were established by QR, a flexible semi-parametric approach of estimating rates of change across the entire distribution of AFV rather than just in the mean as is observed with standard linear regression.


RESULTS
The study evaluated 379 women with normal singleton pregnancies between 16 and 41 weeks gestation. QR was used to determine the association between AFV and gestational age (GA). A second-order quantile regression model indicated a nonlinear relationship between AFV and gestational age at the upper centile range (≥80th percentile).


CONCLUSIONS
This study defines normative centile charts for true AFVs between 16 and 41 weeks gestation in normal singleton pregnancies using QR. This statistical approach more appropriately reflects true AFV across gestation at each centile of interest (e.g. 5th, 50th, 95th, etc.) as compared to standard linear regression.
Department of Obstetrics and Gynecology, University of Arkansas for Medical Sciences, 4301 W. Markham St. Slot # 518, Little Rock, 72205, AR, USA.
Adam T
AT
Sandlin
Songthip T
ST
Ounpraseuth
Horace J
HJ
Spencer
Courtney L
CL
Sick
Patrick M
PM
Lang
Everett F
EF
Magann
D000328:Adult; D000653:Amniotic Fluid / Q000000981:diagnostic imaging*; D002585:Cesarean Section; D004395:Dye Dilution Technique; D005260:Female; D005865:Gestational Age; D006801:Humans; D008922:Mississippi; D016104:Oligohydramnios / Q000000981:diagnostic imaging; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011446:Prospective Studies; D012016:Reference Values; D012044:Regression Analysis; D016216:Ultrasonography, Prenatal / Q000379:methods*