Objective: To study the site and size of the corpus luteum (CL) across the first trimester of pregnancy.
Design: Retrospective observational study of 1,806 ultrasound scans performed at 5 to 9 (+6 d) weeks' gestation, as well as a prospective study (n = 313) performed at 10 to 13 (+6 d) weeks' gestation.
Setting: Four ultrasound practices across Victoria, Australia.
Patient(s): Two thousand one hundred nineteen pregnant women.
Intervention(s): Transvaginal ultrasound.
Main outcome measure(s): Side and size (diameter) of the CL.
Result(s): At 5 to 9 weeks' gestation, the mean CL diameter was 19.3 mm, with no statistically significant variation across each gestational week. Corpus luteum size then statistically significantly declined at 10 to 13 weeks' gestation, with a mean diameter of 16.85 mm. Of 237 women in whom both ovaries were visualized at 10 to 13 weeks' gestation, a CL was seen in 82% of cases. A statistically significant right-sided bias was observed in both groups (54% at 5-9 wk gestation, 56% at 10-13 wk).
Conclusion(s): The CL remains static in size across 5 to 9 weeks' gestation, then its size declines or it disappears from 10 to 13 weeks. A novel right-sided ovulation bias occurs in human beings.