Main Findings
The principal findings of this study are as follows: (1) In the study population (dataset 2), 25,408 (4.76%) women had a history of diagnosed myoma(s) but no myomectomy, and 6,642 (1.24%) women received myomectomy before pregnancy.; (2) Women who have had a myomectomy had significantly higher risks of cesarean section, placenta previa, preterm birth, LBW, and uterine rupture, but a lower risk of LGA, than did women without a history of diagnosed myoma.; (3) The incidence of uterine rupture was significantly higher at delivery within one year after myomectomy (0.71%) than during any longer delivery interval after myomectomy.; (4) Women with a history of diagnosed myoma had significantly higher risks of cesarean section and placenta previa, but no significantly increased risks of preterm birth, LBW, or uterine rupture, compared to women without a history of diagnosed myoma.
Interpretation
Previous studies have also reported increased adverse pregnancy outcomes, including abnormal placentation, such as placenta previa or placenta accreta,10–12 preterm delivery, cesarean delivery, uterine rupture, and postpartum bleeding, in women with a history of myomectomy.13–16 The true incidence of uterine rupture during subsequent pregnancy following myomectomy is difficult to establish, because most of the studies have been cases, case series, or small retrospective cohort studies that do not account for the total number of pregnancies achieved after myomectomy and their consequent outcomes. The incidences of preterm birth and uterine rupture after myomectomy have been variously reported to range from 3.1–35% and from 0.2 to 3.7%, respectively.17, 18 The previous systematic review including all cohort studies with at least five cases demonstrated that the overall incidence of uterine rupture after myomectomy was 0.93% (0.45–1.92%) (n = 7/756); specifically, it was 0.47% (0.13–1.70%) (n = 2/426) in women undergoing a trial of labor after myomectomy, and 1.52% (0.65–3.51%) (n = 5/330) in women before the onset of labor.5 However, the number of pregnancies and viable deliveries after prior myomectomy were 2,367 and 1,284, respectively, from a total of 23 studies. In our study, pregnancy outcomes were available for 9,890 women with a history of myomectomy, which was the largest population. In the previous studies, although uterine rupture occurred at various gestation, it occurred more often before the onset of labor, with a high rate of fetal loss. 18.5 In this study, the incidence of uterine rupture in women with a history of myomectomy was 0.22%, which is less than the reported incidence of uterine rupture (0.4–0.7%) in a trial of labor after cesarean Sect. 19,20 Possible reasons can be a missing diagnosis when uterine rupture is combined with abruptio placenta or antepartum/postpartum bleeding in the middle of pregnancy. Also, uterine dehiscence can be underdiagnosed, based on the data from diagnostic code. However, in this study, women with a history of myomectomy had more than a 12-fold risk of uterine rupture over that of women without a diagnosed myoma. Therefore, counseling for myomectomy in women who desire a pregnancy in the future should discuss the risk of adverse pregnancy outcomes, especially uterine rupture during pregnancy, which can be associated with fetal loss.
In a previous comparison study about delivery outcomes between pregnancies following myomectomy and myoma-complicated pregnancies, the latter showed better outcomes, including fewer cesarean sections, preterm births, and less blood loss, than did pregnancies after myomectomy, which were similar to the results of this study21 A prospective, randomized, multicenter study in couples with unexplained infertility demonstrated no significant difference in conception, placenta previa, preterm labor, postpartum hemorrhage, or live birth rates in women with non-cavity distorting myomas and those without myomas.22 A recent retrospective cohort study23 revealed that women with a history of myomectomy were associated with a 180% increased risk of intraoperative transfusion, were 713% more likely to experience a bowel injury, and were 243% more likely to undergo a cesarean hysterectomy. These findings provide reassurance that pregnancy success is not affected in couples with non-cavity distorting myomas undergoing assisted reproductive treatment (ART) for unexplained infertility.
Previously, ACOG stated that myomectomy should be considered for a woman with uterine leiomyomas who has undergone several unsuccessful IVF cycles despite appropriate ovarian response and good-quality embryos.24 SOGC, ASRM, and French guideline also stated that intramural myomas may have a negative effect on fertility, but treating them does not improve fertility, and myomectomy is therefore indicated only for symptomatic myomas,8,24,25 They emphasized that information should be provided about the risk of uterine rupture during a future pregnancy, before planning a myomectomy in women who might become pregnant later on.
Strengths and Limitations
A limitation of this study was our lack of data on number, size, or type of myomas, type of closure after myomectomy, number of suture layers, and use of electrocauterization, which may have important clinical significance. Also, there was no information on the type of myomectomy (laparoscopic, open, hysteroscopic, or robot-assisted) or type of conception (natural, OS, OS-IUI, or IVF). Last, data about gestational age at uterine rupture was not available.
However, this study included the largest population in the group with a history of diagnosed myoma(s) with and without myomectomy. In addition, the nationwide design of the original database can provide more generalized outcomes in pregnancies with diagnosed myoma(s) and with previous myomectomy. In addition, to our knowledge, this is the first study about incidence of uterine rupture in women with myomectomy, according to delivery time interval after myomectomy. The incidence of uterine rupture was highest within one year after surgery, which suggests that pregnancy with or without ART should be delayed at least 3–6 months. Last, we compared pregnancy outcomes in three groups: women with diagnosed myoma(s), with previous myomectomy, and without a diagnosed myoma or myomectomy. Although both groups of women with myoma and women with previous myomectomy showed adverse pregnancy outcomes, women with a previous myomectomy demonstrated more risks of adverse pregnancy outcomes, including preterm birth, low birth weight, cesarean section, and uterine rupture. These results might be useful in counseling when a woman, who might become pregnant later on, is diagnosed with uterine myoma.