Corpus luteum across the first trimester: size and laterality as observed by ultrasound

ObjectiveTo study the site and size of the corpus luteum (CL) across the first trimester of pregnancy.DesignRetrospective 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.SettingFour 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.