Reference intervals of gestational sac, yolk sac and embryo volumes using three-dimensional ultrasound.
OBJECTIVE
To create reference intervals of gestational sac volume (GSV), yolk sac volume (YSV), embryo volume (EV), crown-rump length (CRL) and gestational sac diameter (GSD) in the first trimester of pregnancy using three-dimensional ultrasound.


METHODS
Women in the first trimester of pregnancy were invited to participate in the study. Inclusion criteria were well-established dates, and that the women were non-smokers and healthy, without any medical disorders. Three-dimensional ultrasound volumetric data (GSV, YSV, EV) were collected together with standard two-dimensional measurements of CRL and GSD. For each measurement separate regression models were fitted to estimate the mean and SD at each gestational age. The 5(th), 50(th) and 95(th) centiles were derived using a combination of these regression models.


RESULTS
One hundred and sixty-six women at between 6 and 12 weeks' gestation were scanned once. The mean ( +/- SD) maternal age was 29.4 ( +/- 5) years. There were no miscarriages and no congenital abnormalities were noted. Mean gestational age at delivery was 39.3 ( +/- 1.4) weeks and mean birth weight was 3.3 ( +/- 0.4) kg. The CRL centiles fitted a cubic model and the GSD centiles fitted a linear model. The centiles for YSV fitted a quadratic model on the modified log-transformed data. The centiles for GSV and EV were modeled using quantile regression.


CONCLUSIONS
Reference intervals and centile charts for first-trimester GSV, YSV and EV have been created in addition to CRL and GSD using rigorous methodology.
Department of Obstetrics and Gynaecology, Nelson R Mandela School of Medicine, University of Kwa-Zulu Natal, South Africa. bagrateej1@ukzn.ac.za
J S
JS
Bagratee
L
L
Regan
V
V
Khullar
C
C
Connolly
J
J
Moodley
D000328:Adult; D001724:Birth Weight / Q000502:physiology; D003430:Cross-Sectional Studies; D018568:Crown-Rump Length; D004622:Embryo, Mammalian / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006801:Humans; D021621:Imaging, Three-Dimensional; D009929:Organ Size; D011247:Pregnancy; D011256:Pregnancy Outcome; D011261:Pregnancy Trimester, First; D012016:Reference Values; D012044:Regression Analysis; D016216:Ultrasonography, Prenatal / Q000379:methods*; D015017:Yolk Sac / Q000000981:diagnostic imaging* / Q000254:growth & development