Results
Among 761 infertile women with reproductive surgery, 428 (56.2%) women conceived spontaneously, and 333 (43.8%) conceived after IVF/ICSI. There were 58 pairs of twins (7.23%). The incidence of twin pregnancies was lower after spontaneous conception than after IVF/ICSI (11 (2.6%) vs. 47 (14.1%); P-value <0.001).
The most common indication for fertility treatment was endometriosis (228; 32.4%) with no significant difference between the spontaneous conception and IVF/ICSI group (Table S1).
Among 761 infertile women, 703 women had a singleton pregnancy. Compared with women who conceived spontaneously, women who conceived after IVF/ICSI were significantly older (33.08±3.13 vs. 31.81±2.24; P-value <0.001), more often older than 35 years (37.4% vs. 27.3%, P-value 0.005), and nulliparous (90.2% vs. 81.5%; P value 0.002) (Table S2). We found no significant differences between spontaneous and IVF/ICSI conception concerning the pre-gestational BMI, pre-gestational BMI < 18.5 kg/m2, pre-gestational BMI ≥ 30 kg/m2, GWG z-score, GWG z-score >+2, or >-2, pre-gestational hypertension, pre-gestational diabetes, chronic kidney disease, other chronic diseases, conization, uterine anomalies, hysteroscopy (diagnostic/therapeutic), smoking during pregnancy, previous preterm delivery, preeclampsia/eclampsia, gestational diabetes and birth of an SGA neonate (Table S2). Univariate analysis showed that women who conceived after IVF/ICSI significantly more often delivered < 32 gestational weeks (3.8% vs. 1.4%; P value 0.041) (Table S2). However, logistic regression analysis adjusted for maternal age and nulliparity disclosed no significant association between the mode of conception and all preterm deliveries < 37 gestational weeks, spontaneous preterm deliveries < 37 weeks, as well as all preterm deliveries < 32 gestational weeks (Table 1).
In the second part of the study, we evaluated the effect of reproductive surgery on preterm delivery as a treatment-related adverse outcome. Almost half of the women in the infertility group conceived after IVF/ICSI (43.8%). Compared with fertile women before PS matching, infertile women were older at delivery, more often nulliparous, they more often suffer from chronic diseases, had uterine anomalies, and miscarriage previously, all of which may increase the risk of preterm delivery (Table 2). Also, among infertile women, there were more of those who had numerous co-existent risk factors for preterm delivery (Figure 1). After PS matching, the fertile and infertile women were well balanced for the chosen possible risk factors for preterm delivery, also concerning the number of co-existent risk factors per woman (Figure 1, Table 2). In the PS matched sample, the incidences of preterm delivery < 37 and < 32 gestational weeks were higher in the infertile women. However, the differences did not reach a statistical significance (Table 3).
Using PS matching, we also calculated the odds of preterm delivery in the group of infertile women who conceived spontaneously and after IVF/ICSI separately and found no significant differences compared with fertile women. Compared with fertile women, the odds of preterm delivery < 37 weeks in infertile women who conceived spontaneously was 1.51 (95%CI 0.93-2.43; p-value 0.093), and < 32 weeks was 0.72 (95%CI 0.29-1.81; p-value 0.486). Compared with fertile women, the odds of preterm delivery < 37 weeks in infertile women who conceived after IVF/ET was 1.29 (95%CI 0.86-1.94;p-value 0.217), and < 32 weeks was 1.09 (95%CI 0.48-2.52; p-value 0.832).