In one of the first studies to examine the reasons for the rising number of women delivering their babies by cesarean section, Yale School of Medicine researchers found that while half of the increase was attributable to a rise in repeat cesarean delivery in women with a prior cesarean birth, an equal proportion was due to a rise in first time cesarean delivery. Among these deliveries, factors such as slowly progressing labor and fetal heart rate concerns were the largest contributors.

The U.S. cesarean delivery rate has increased dramatically over the past decade, with some of the highest increases noted in Connecticut and Rhode Island. Much of the previous research on the reasons for this increase is limited to birth certificate data, which does not record the specific indication or reason for cesarean delivery.

Pre-released online and published in the July issue of Obstetrics & Gynecology, the study was led by Yale researcher Jessica Illuzzi, M.D., of the Department of Obstetrics, Gynecology & Reproductive Sciences. Illuzzi and her co-authors analyzed indications for cesarean delivery on prospectively collected data from over 30,000 births at Yale-New Haven Hospital from 2003 to 2009.

"We found that more objective reasons, such as the baby being in a breech position and placenta previa, remained stable over time, while less objective reasons, such as slow progress in labor and concerns about fetal heart tracings contributed large proportions (>50%) to the increasing primary cesarean delivery rate," said Illuzzi.

In addition, suspected large infants, twin pregnancies, and preeclampsia contributed to the increase despite relatively stable rates of these conditions in the population during the seven-year study. "This suggests that the use of cesarean for these indications is increasing," said Illuzzi.

The researchers also examined some of the commonly cited reasons for increasing cesarean rates. "Despite speculation that the decreasing use of forceps and vacuum-assisted vaginal delivery have led to increasing cesarean delivery rates, our data shows that since 2003 the increase in cesarean for labor arrest disorders was manifested in the first stage of labor prior to full dilation when forceps or vacuum are not appropriate." In addition, maternal-choice cesarean births, often cited as another factor, contributed only a small proportion (8%) to the total increase in primary cesarean delivery in the study.

"Elucidating the reasons for the rise in cesarean delivery can help us consider if the benefits of the surgery based on indication appropriately outweigh the known risks, costs and longer recovery time," said Illuzzi.

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Yale authors on the study included Emma L Barber, Lisbet S. Lundsberg, Kathleen Belanger, Christian M. Pettker and Edmund Funai.

Citation: Obstetrics & Gynecology doi: 10.1097/AOG.0b013e31821e5f65