Caughey, MD, Ph D, Department of Obstetrics and Gynecology, University of California, San Francisco, 505 Parnassus Avenue, Box 0132, San Francisco, CA 94143, O: 415-514-9322, P: 415-443-0301, F: 415-476-1811, E: We conducted a retrospective cohort study of all term, singleton pregnancies delivered at our institution who had an OBUS at ≤24 weeks of gestation.
Statistical significance was designated by a p-value less than 0.05.
This study was approved by the Committee on Human Research at UCSF.
Otherwise, the EDC from the earliest ultrasound was used.
The primary outcomes examined were the whether the pregnancy proceeded beyond 41 or 42 weeks of gestation.
The primary outcome measures were the rates of postterm pregnancies greater than 41 or 42 weeks’ gestation.
Secondary outcomes were the differences between the postterm and term gestations in maternal and neonatal outcomes.
We designed a retrospective cohort study of all women delivered beyond 37 weeks gestational age from January 1, 1992 to December 31, 2001 at Moffitt-Long Hospital affiliated with the University of California, San Francisco (UCSF) in order to compare women who experienced a first trimester ultrasound (OBUS12 - less than or equal to 12 weeks gestation) to those who experienced a second trimester ultrasound (OBUS13–24 - 13 to 24 weeks gestation).
Medical records were abstracted to determine whether women had received an obstetric ultrasound during their pregnancy.
In the setting of each of these events, an estimated date of confinement (EDC) is incorrect and leads to women’s gestational age at delivery being incorrect.
With oligo-ovulation or incorrect recall, a woman may have actually ovulated later than predicted by the LMP, and is thus at an earlier gestational age than predicted.
Finally, outcomes between pregnancies that had progressed beyond 41 weeks of gestation were compared to those less than 41 weeks of gestation in each ultrasound group to determine whether experiencing an earlier ultrasound had an effect on measured differences in perinatal outcomes.