Comparison of uterine fibroids’ growth pattern during pregnancy according to fetal sex: an observational study

BACKGROUND: To investigate the effect of fetal sex on fibroids’ growth during pregnancy according to the hCG serum levels METHODS: Observational study conducted from January 2007 to December 2016 on women with ultrasound identification of uterine fibroids who had a pregnancy within 1 year from diagnosis. The fibroids diameter was determined during the pre-pregnancy ultrasound, early first trimester (5–7 weeks), late first trimester (11–13 weeks), second trimester (19–21 weeks), and third trimester (31–33 weeks). The diameter growth was calculated in each interval between two ultrasounds. The hCG serum levels were determined both in early and late first trimester. The correlation between hCG levels and fibroid diameter was evaluated. Obstetric outcomes collected were gestational weeks at birth and the rate of cesarean section. Neonatal outcomes were birthweight and Apgar score at 1 min. RESULTS: Eighty-seven of the included women had a male fetus, and 70 had a female fetus. A progressive increase of fibroid diameter was observed from pre-pregnancy to second trimester for both fetal sexes. In third trimester, the mean ± SD fibroid diameter of female fetuses showed a slowdown, while the mean ± SD fibroid diameter of male fetuses continued to grow. Women carrying a female fetus presented a higher fibroid diameter in early first trimester (33.5 ± 13.3 mm vs 27.4 ± 11.0 mm, p < 0.01), late first trimester (40.2 ± 13.9 mm vs 34.6 ± 11.7 mm, p < 0.01), and second trimester (40.5 ± 14.9 mm vs 34.7 ± 10.3 mm, p < 0.01). The hCG serum levels resulted higher in women with a female fetus: 61406 (50554-71760) mU/ml vs 46016 (37160-56744) mU/ml (p < 0.01). A positive correlation between hCG levels and fibroid diameter was found both for male and female fetuses (male r = 0.77, 95% CI 0.71–0.82, p < 0.01 and female r = 0.82, 95% CI 0.76–0.86, p < 0.01). CONCLUSION: Women with female fetus seem to have a higher growth of fibroids up to second trimester of pregnancy. This process may be mediated by the higher serum hCG levels found in women expecting a female fetus.