title: Incidence and significance of unequal gestational sac diameter or embryo crown-rump length in twin pregnancy.
abstract: The incidence of differences in gestational sac diameter and crown-rump length, measured at the time of the first ultrasound, in which at least one gestational sac or crown-rump length could be visualized, were analysed retrospectively in 260 twin pregnancies in which one or both fetuses were delivered at term. The difference in gestational sac diameter averaged 1.2 +/- 0.1 mm for pregnancies which ended in twin births, compared to 2.0 +/- 0.3 mm when pregnancy ended in single births (P less than 0.02). The difference in crown-rump length averaged 2.4 +/- 0.6 mm for pregnancies which ended in a single birth, compared to 0.9 +/- 0.1 mm for twin births (P = 0.02). Disparities of greater than or equal to 3 mm in gestational sac diameter (P less than 0.05) or crown-rump length (P less than 0.001) were associated with an embryo loss rate greater than or equal to 50%. The disparity in gestational sac diameter (P less than 0.04) and crown-rump length (P less than 0.01) was smaller in pregnancies resulting from assisted reproductive technologies, compared with pregnancies resulting from coitus or insemination. Differences in gestational sac diameter and crown-rump length in early pregnancy were unrelated to differences in birth weight, length or sex.
authors.affiliation: Fertility Institute, Department of Obstetrics and Gynecology, New Orleans, LA.
authors.forename: R P
authors.initials: RP
authors.lastname: Dickey
authors.forename: T T
authors.initials: TT
authors.lastname: Olar
authors.forename: S N
authors.initials: SN
authors.lastname: Taylor
authors.forename: D N
authors.initials: DN
authors.lastname: Curole
authors.forename: P H
authors.initials: PH
authors.lastname: Rye
authors.forename: E M
authors.initials: EM
authors.lastname: Matulich
authors.forename: M H
authors.initials: MH
authors.lastname: Dickey
mesh_terms: D005321:Extraembryonic Membranes / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005260:Female; D005313:Fetal Death; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D014427:Twins; D014463:Ultrasonography