The influence of maternal body mass index on fetal weight estimation in twin pregnancy.
OBJECTIVE
Sonographic estimated fetal weight (EFW) is important in the management of high-risk pregnancies. The possibility that increased maternal body mass index (BMI) adversely affects EFW assessments in twin pregnancies is controversial. The aim of this study was to investigate the effect of maternal BMI on the accuracy of EFW assessments in twin gestations prospectively recruited for the ESPRiT (Evaluation of Sonographic Predictors of Restricted growth in Twins) study.


METHODS
One thousand one twin pair pregnancies were recruited. After exclusion, BMI, birthweights, and ultrasound determination of EFW (within 2 weeks of delivery) were available for 943 twin pairs. The accuracy of EFW determination was defined as the difference between EFW and actual birthweight for either twin (absolute difference and percent difference). Cells with less than 5% of the population were combined for analysis resulting in the following 3 maternal categories: (1) normal/underweight, (2) overweight, and (3) obese/extremely obese.


RESULTS
Analysis of the 3 categories revealed mean absolute variation values of 184 g (8.0%) in the normal/underweight group (n = 531), 196 g (8.5%) in the overweight group (n = 278), and 206 g (8.6%) in the obese/extremely obese group (n = 134) (P = .028, which was nonsignificant after adjustment for multiple testing). Regression analysis showed no linear or log-linear relationship between BMI and the accuracy of EFW (P value for absolute difference = .11, P value for percentage difference = .27).


CONCLUSIONS
Contrary to a commonly held clinical impression, increasing maternal BMI has no significant impact on the accuracy of EFW in twin pregnancy.
Clinical Science Institute, National University of Ireland Galway, Galway, Ireland.
Helen M
HM
Ryan
Clinical Science Institute, National University of Ireland Galway, Galway, Ireland. Electronic address: john.morrison@nuigalway.ie.
John J
JJ
Morrison
Department of Obstetrics and Gynaecology, Royal College of Surgeons in Ireland, Dublin, Ireland; Department of Obstetrics and Gynaecology, Rotunda Hospital, Dublin, Ireland.
Fionnuala M
FM
Breathnach
Department of Obstetrics and Gynaecology, University College Dublin School of Medicine and Medical Science, University College Dublin, Dublin, Ireland; Department of Obstetrics and Gynaecology, National Maternity Hospital, Dublin, Ireland.
Fionnuala M
FM
McAuliffe
Department of Obstetrics and Gynaecology, Rotunda Hospital, Dublin, Ireland.
Michael P
MP
Geary
Department of Obstetrics and Gynaecology, Coombe Women's and Infants' University Hospital, Dublin, Ireland.
Sean
S
Daly
Department of Obstetrics and Gynaecology, University College Cork, Cork, Ireland.
John R
JR
Higgins
Department of Obstetrics and Gynaecology, Royal Victoria Maternity Hospital Belfast, Belfast, Northern Ireland, United Kingdom.
Alyson
A
Hunter
Department of Obstetrics and Gynaecology, Graduate Entry Medical School, University of Limerick, Limerick, Ireland.
Gerard
G
Burke
Department of Obstetrics and Gynaecology, Our Lady of Lourdes Hospital, Drogheda, Ireland.
Shane
S
Higgins
Department of Obstetrics and Gynaecology, National Maternity Hospital, Dublin, Ireland.
Rhona
R
Mahony
Department of Obstetrics and Gynaecology, Royal College of Surgeons in Ireland, Dublin, Ireland.
Patrick
P
Dicker
Department of Obstetrics and Gynaecology, Royal College of Surgeons in Ireland, Dublin, Ireland.
Fiona
F
Manning
Department of Obstetrics and Gynaecology, Royal College of Surgeons in Ireland, Dublin, Ireland.
Elizabeth
E
Tully
Department of Obstetrics and Gynaecology, Royal College of Surgeons in Ireland, Dublin, Ireland; Department of Obstetrics and Gynaecology, Rotunda Hospital, Dublin, Ireland.
Fergal D
FD
Malone
D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D005260:Female; D020567:Fetal Weight; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D059285:Pregnancy, Twin; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal; D055815:Young Adult
body mass index; estimated fetal weight; sonographic fetal weight; twin pregnancy