In this study,  Women who have had a myomectomy had higher risks of cesarean section, placenta previa, preterm birth, LBW, and uterine rupture, but a lower risk of LGA, compared to women without a history of diagnosed myoma.;  The incidence of uterine rupture was higher at delivery within one year after myomectomy (0.71%) than during any longer delivery interval after myomectomy.;  Women with a history of diagnosed myoma had higher risks of cesarean section and placenta previa, but no increased risks of preterm birth, LBW, or uterine rupture, compared to women without a history of diagnosed myoma.;  In nulliparous women, both groups of women with a history of diagnosed myoma(s) and women with a history of myomectomy had higher risks of cesarean section, placenta previa, uterine rupture, preterm birth, and LBW, compared to women without a diagnoses myoma.;  Especially, aORs for uterine rupture in women with diagnosed myoma and women who have had a myomectomy were 4.14 and 41.35, respectively, in nulliparous women.
Previous studies have also reported increased adverse pregnancy outcomes, including abnormal placentation, such as placenta previa or placenta accreta [9, 12, 13], preterm delivery, cesarean delivery, uterine rupture, and postpartum bleeding, in women with a history of myomectomy [14,15,16,17]. 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 to 35% and from 0.2 to 3.7%, respectively [18, 19]. 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 . However, the number of pregnancies and viable deliveries after prior myomectomy were 2367 and 1284, respectively, from a total of 23 studies. In our study, pregnancy outcomes were available for 9890 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 [10, 19]. 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 section . Possible reasons can be a missing diagnosis when uterine rupture or dehiscence was combined with placental abruption or antepartum/postpartum bleeding in the middle of pregnancy. 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. In nulliparous women, women with a history of diagnosed myoma(s) and women with a history of myomectomy had 4.14-fold and 41.35-fold higher risks of uterine rupture, compared to it of women without a diagnoses 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 outcomes of pregnancies after myomectomy, which were similar to the results of this study . A recent retrospective cohort study  revealed that women with a history of myomectomy were associated with increased risks of intraoperative transfusion, bowel injury, and a cesarean hysterectomy.
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 . SOGC, ASRM, and French guidelines 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 [5, 23, 24], 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. However, we divided myomectomy group to submucosal or intramural myomas and subserosal or unspecified myomas, based on diagnostic codes. The results were not different according to types of myomas, although it is difficult to define the unspecified myomas. The second limitation was that 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). And data about gestational age at uterine rupture was not available. Lastly, this study did not have data if myomectomy or cesarean section was performed before the study period (2004–2015).
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. 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, in this study. A previous study has reported that incision healing after a caesarean section took at least 6 months for the complete involution and recovery of uterine zonal anatomy by magnetic resonance imaging . The other study also reported that risk of uterine rupture was 3.12 fold in pregnant women less than < 12 months since their last caesarean delivery, compared to it in women more than 24 months since their last caesarean delivery, with the odds of rupture appearing to plateau for intervals beyond 12 months . Lastly, we had subgroup analysis for adverse obstetric outcomes in nulliparous women, because it can clearly eliminate the effects of previous cesarean section, which could be performed before the study period. In nulliparous women, both groups of women with a history of diagnosed myoma(s) and women with a history of myomectomy had higher risks of cesarean section, placenta previa, uterine rupture, preterm birth, and LBW compare to women without a diagnoses myoma. However, the risk of uterine rupture was much higher in women with a history of myomectomy. These results might be useful in counseling when a woman, who might become pregnant later on, is diagnosed with uterine myoma.