Reference curves of symphysis-fundus height in twin pregnancies.

Objective: To generate reliable new reference ranges for symphysis-fundus height (SFH) in twin pregnancies using modern statistical methods and to evaluate whether small-for-gestational age (SGA) babies of women who had a SFH measurement after the 25th gestational week could be predicted by the SFH measurement in the reference curves and other maternal data.

Study Design: In a retrospective cross-sectional study at the obstetric outpatient clinic, Zurich University Hospital, SFH was determined in 257 twin-pregnant women with accurately dateable twin pregnancies (Caucasians: N=217, Asians: N=15, Blacks: N=10, and 15 others). Exclusion criteria were intrauterine fetal death, and known fetal and maternal diseases, which influence SFH. Pregnant women with twins were divided in three groups according to the birth weight of the babies. Group I: both babies were appropriate for gestational age (AGA), group II: one baby was AGA and one SGA, and group III: both babies were SGA.

Results: SFH measurements increased linearly with gestational age (GA). The following rule of thumb is suggested for the 50th centile of SFH (cm)=gestational week+10% of gestational week. Age, height, weight and body mass index (BMI) before pregnancy, parity and ethnic group were insignificant determinants in SFH measurement. A prognostic score for identification of group III was created for a GA> or =25 weeks and BMI<30 kg/m2.

Conclusions: Measuring SFH is simple, inexpensive and non-invasive and may be of some use for identifying twin mothers with SGA twin pairs.