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This is Why the Medical Literature is Confusing!

Adverse obstetric outcomes associated with sonographically identified large uterine fibroids.

Authors: Shavell VI, Thakur M, Sawant A, Kruger ML, Jones TB, Singh M, Puscheck EE, Diamond MP.

From: Wayne State University, Detroit, Michigan

Journal: Fertility Sterility. 2012 Jan;97:107-10

Problem: Studies show mixed results about whether fibroids affect pregnancy or delivery. Many studies are poorly conducted leading to confusion.

Study: To determine if large uterine fibroids (greater than 5 cm in diameter) effect pregnancy and delivery.

Results: Compared to women with no fibroids, women with large fibroids (>5 cm) delivered earlier (38.6 weeks vs. 36.5 weeks). Early rupture of membranes, and early delivery were also more frequent in the large fibroid group, and were associated with number of fibroids >5 cm in diameter. The amount of bleeding after giving birth was more in the large fibroid group (2 cups vs. 2¾ cups), and more women needed a blood transfusion (1% vs. 12%). Please read my comments below…..

Authors’ Conclusions: Women with large uterine fibroids in pregnancy are at significantly increased risk for delivery at an earlier gestational age compared to women with small or no fibroids, as well as obstetric complications including excess blood loss and increased frequency of postpartum blood transfusion.

Dr. Parker’s Comments: This is not a good study and will mislead many doctors and their patients into unnecessary fear about fibroids and pregnancy. This is an extremely small number of women, 95 in each group, and the women with fibroids bigger than 5cm was much smaller (42). It is almost impossible to do statistical analysis with such small groups and the conclusions are likely to be meaningless. My own feeling is that this paper should never have been published and I am in the process of writing a letter to the editor to discuss the problems with the paper.

Compare the current study with a much better study by Stout published in 2010 (reference below). That study included 2,058 pregnant women who had fibroids and compared them with 61,989 pregnant women without fibroids. Stout reported very small (less than 2%) differences for the pregnancies: placenta previa (placenta located low in the uterus), placental abruption (placenta separating from the uterus early), ruptured membranes, and early birth before 34 weeks. Again, the differences were ALL LESS THAN 2%. (OB GYN 2010;116:1056). For more about this the Stout study see this prior blog post: Fibroids (leiomyomas) at routine second-trimester ultrasound examination and adverse obstetric outcomes.

Also, in the current study, other risk factors for early delivery, bleeding or other problems during pregnancy (maternal age, smoking, alcohol use, diabetes, high blood pressure, previous early birth, vaginal bleeding during pregnancy) were not factored in, but these risks were factored in to the Stout study. This is a major problem with the study and, in my mind, undermines most of the findings.

While the risk of having a blood transfusion was clearly much higher for women with large fibroids, the authors do not tell us why the transfusions were done. In the past few years, doctors have been more diligent about avoiding transfusions unless blood counts get very low (less than 7 hemoglobin) and I doubt this trend was followed in this study.

Although the Stout study found that women with large fibroids (larger than 5 cm) did have a higher risk of fetal death, this occurred rarely (2% of women with large fibroids) but we are not told the causes. So, it is hard to understand why this would be true.

It is very hard to read medical articles, or even read the lay press interpretation of medical articles. All authors (me included) try to make their research sound as important as they can. You really need to pay attention to the details, have a healthy skepticism and ask lots of questions.


Disclaimer: The ideas, procedures and suggestions contained on this web site are not intended as a substitute for consulting with your physician. All matters regarding your health require medical supervision.

Fibroid Doctor William H. Parker

Dr. William H. Parker is a board-certified Fellow in the American College of Obstetricians and Gynecologists. Dr. Parker is an internationally recognized expert in fibroid surgery and research. Based in San Diego, California, he is considered one of the best fibroid surgeons for abdominal and laparoscopic myomectomy in the United States and abroad. He has been chosen for Best Doctors in America and Top Doctors every year beginning in the late 90's.

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