While nearly 1 in 5 patients have a retroverted uterus, this aspect has garnered limited attention in perinatal research to date[1], [2]. In the present study, we found that nulliparous patients with a retroverted uterus have decreased rates of spontaneous pregnancies, thereby requiring IVF treatment in comparison to their counterparts with an anteverted uterus. Our finding stands a two-fold elevation from the globally reported rates of 1–5% for all pregnancies[10], [15], [16]. Nevertheless, in nulliparous patients attempting vaginal deliveries, our analysis showed no differences in adverse perinatal outcomes between the groups.
The literature regarding pre-gestational uterine position and spontaneous pregnancy is scarce. While the exact reasons remain unclear, some studies[10], [15], [16], [17] propose that a retroverted uterus might alter sperm transport or embryo implantation efficiency. On the other hand, the clinical pregnancy rate was found to be comparable when using IVF among patients with anteverted and retroverted uterus[18]. Our initial theory appears to be supported based on the above notions and current study findings of a possible association between a retroverted uterus and a lower likelihood of natural conception. Initially, it is suggested that a retroverted uterus with a pronounced posterior flexion might impede the natural postcoital sperm transport toward the fallopian tubes, potentially compromising the probability of natural conception. Secondly, during IVF, the fertilized ovum is transferred directly into the uterine cavity under ultrasound guidance. This process bypasses any obstacles related to uterine angulation or the presence of uterine anomalies. Consequently, it ensures a successful IVF implantation irrespective of uterine position.
Evidence supporting the association between the retroverted uterus and the heightened need for IVF could be further extrapolated from a sub-analysis of the causes of IVF. Unexplained infertility, accounting for over 60% of cases, prevailed as the primary indication for IVF in both retroverted and anteverted groups. This finding underscores the possibility of other underlying factors contributing to the need for IVF within this subset of unexplained infertility patients, of which retroverted uterus could be a contributing factor.
Contrary to our initial hypothesis, the study findings did not indicate a higher incidence of adverse pregnancy outcomes, particularly of intrapartum cesarean deliveries, among nulliparous patients attempting vaginal deliveries in the retroverted group compared to the anteverted group. A plausible explanation might be the "autocorrection" phenomenon[3], [19], [20], [21], [22], [23]. During pregnancy, particularly in the early second trimester beyond 14 weeks of gestation, any retroverted uterus typically autocorrects itself, rises out of the hollow of the sacrum, and assumes an anterior ventral position[3]. If this physiological autocorrection adaptation fails, the axis of the retroverted uterus is altered, and the cervix is anteriorly placed in the vagina close to the bladder, leading to reported cases of incarceration[11], [12].
Our study possesses robust strengths. It is the first to explore the association between uterine position and the necessity for IVF. Additionally, we ensured reliability through formal documentation of uterine position via transvaginal ultrasound in all cases. Furthermore, our homogeneous study population and utilization of a real-time electronic database minimize the possibility of bias. Several limitations warrant acknowledgment. Firstly, our reliance on data from a single tertiary center may limit the generalizability of findings. Secondly, our sample size remained relatively small despite an extended study period due to historical documentation practices, excluding potential participants. Lastly, the retrospective nature of our study introduces constraints associated with incomplete database capture.
In conclusion, our findings suggest an association between a retroverted uterus and a higher likelihood of conceiving after IVF treatment. They also underscore the importance of thorough fertility evaluation for patients with a retroverted uterus, mainly when infertility causes are not readily apparent. Importantly, our findings provide reassurance by suggesting that a retroverted uterus does not correlate with adverse pregnancy outcomes during attempted vaginal delivery. Prospective studies are warranted to ascertain our findings.