Temporal Trends in Caesarean Section Rates Following Assisted Reproductive Technology: Why Declining Twin Rates Have Not Reduced Caesarean Deliveries — A 15-Year Single-Centre Analysis of 26 692 Cycles

For couples struggling to conceive, modern medicine offers a powerful set of tools known as assisted reproductive technology. These procedures, which include fertilizing an egg outside the body and placing an embryo back into the uterus, have helped millions of families grow. Over the last two decades, doctors have made significant safety improvements to these treatments. The most notable change has been the shift toward transferring only one embryo at a time, a practice designed to prevent the dangerous complications that often arise when twins are born. Because carrying twins puts a heavy strain on the body, it has long been assumed that reducing twin pregnancies would automatically lead to fewer emergency surgeries to deliver babies.

Yet, a curious contradiction has emerged in the medical world. While the number of twin births has dropped dramatically, the rate of cesarean sections—surgical deliveries—has not gone down. In fact, it has continued to climb. This puzzle sits at the intersection of fertility treatment and obstetrics, raising a critical question for doctors and parents alike: if we have successfully reduced the most obvious risk factor for surgical birth, why are more women still undergoing surgery? Understanding this trend is vital, as cesarean sections are major operations that carry their own risks for mothers and newborns, and knowing the true drivers behind their rising frequency is essential for safer care.

Researchers at the Quanzhou Women's and Children's Hospital in China set out to solve this mystery by looking at a massive collection of medical records spanning fifteen years. They examined nearly 27,000 treatment cycles, tracking every step from the initial fertility procedure to the final birth. Their goal was to see how the landscape of assisted reproduction had changed over time and to pinpoint exactly why the rate of surgical deliveries kept rising even as twin births fell. The team divided the data into four distinct time periods, allowing them to watch the trends unfold year by year, much like observing a long-term experiment in human health.

The study confirmed that the medical community's efforts to improve safety were working. The rate of twin deliveries, which started at nearly 28 percent in the early years of the study, dropped to 12 percent by the end. This was a direct result of doctors transferring fewer embryos, often just one, per cycle. Alongside this success, the rate of babies born too early also decreased, and the overall success rate of the treatments improved, with more women achieving healthy pregnancies despite getting older on average. The average age of the women seeking treatment rose from about 30 to 33 years, and the proportion of women over 35 nearly doubled, reflecting a broader societal trend of delaying parenthood.

Despite these clear victories in safety and success, the rate of cesarean sections told a different story. It began at 62 percent and climbed steadily to nearly 71 percent over the fifteen-year period. The researchers discovered that the decline in twins was not enough to offset other powerful forces at play. The primary driver of this increase was a shift in the type of treatment used. In the early years, most successful pregnancies came from fresh embryo transfers, where the embryo is placed in the uterus shortly after it is created. Over time, however, the medical community moved toward freezing embryos and transferring them later in a separate cycle. This method, known as frozen-thawed embryo transfer, became the dominant approach, accounting for 64 percent of live births by the end of the study.

The data revealed that pregnancies resulting from these frozen transfers carry a significantly higher risk of requiring a cesarean section compared to those from fresh transfers. While fresh transfers resulted in surgical deliveries about 61 percent of the time, frozen transfers led to surgery in 73 percent of cases. As the number of frozen transfers grew, it pulled the overall cesarean rate up, effectively canceling out the benefits gained from having fewer twins. Additionally, the increasing age of the mothers contributed to the rise, as older mothers naturally face a higher likelihood of needing surgical delivery. The combination of these two factors—the shift to frozen embryos and the aging of the patient population—created a perfect storm that drove cesarean rates higher, even as the treatments themselves became safer in other ways.

The study also highlighted a cultural factor that may be influencing these numbers. In regions where cesarean sections are already very common, there is often a perception that pregnancies achieved through fertility treatments are too precious to risk. This mindset can lead parents and doctors to choose surgery as a default option, viewing it as a safer, more controlled path for these high-stakes pregnancies. While the researchers could not measure this sentiment directly in their data, they noted that the high baseline rate of surgery in the region suggests that this cultural inertia plays a role. The findings suggest that the safety of a pregnancy is not determined solely by whether it is a singleton or a twin, but also by the specific medical path taken to achieve it and the age of the mother.

Ultimately, this long-term analysis reveals that the journey to a healthy birth is complex and that improvements in one area can be masked by changes in another. The reduction in twin births was a genuine public health success, preventing many premature births and complications. However, the rise in cesarean sections shows that the medical community must look beyond the number of embryos transferred. The shift toward frozen embryo transfers, while beneficial for many reasons, appears to introduce new risks that require careful management. For doctors and families, the lesson is clear: a pregnancy following fertility treatment should be treated with the same level of nuanced care as any other, recognizing that the method of conception and the age of the mother are just as important as the number of babies expected. The path forward involves tailoring delivery plans to the specific risks of each pregnancy rather than relying on old assumptions or defaulting to surgery.