This retrospective cohort study examines the association between previous mode of delivery and subsequent live birth rate in women who become pregnant after in vitro fertilization (IVF) or intra cytoplasmic sperm injection (ICSI) after their first delivery. The study included 112 women with a previous caesarean section and 418 women with a previous vaginal delivery, and a total of 1588 embryo transfers between January 2005 and June 2016 (Leiden University Medical Centre, the Netherlands). The mean age was 35 years and mean number of embryos transferred per attempt, 1.18. The study population included a total of 429 pregnancies resulting in 296 live births. The crude odds ratio for a subsequent live birth per embryo transfer was 0.60 (CI; 0.44 to 0.83, p ¼ 0.002) in women with a previous caesarean section compared to women with a previous vaginal delivery. After adjustment for age, fresh/frozen-thawed embryo transfer and quality of the embryo, the odds ratio was 0.64 (CI; 0.46 to 0.89, p ¼ 0.01). It was concluded that in subfertile women trying to achieve a subsequent pregnancy with IVF or ICSI, a history of caesarean section was associated with a reduced live birth rate per embryo transfer compared to women with a history of one previous vaginal delivery.

Measurement of pH in IVF-media using the blood gas analyzer (BGA) requires validation, because IVF-media is outside the intended scope of the BGA. To determine whether the Siemens Rapidpoint 500 BGA is suitable for pH measurements in IVF-media this study will validate the BGA and assess its accuracy. In this method comparison study, the pH of over three hundred IVF-media samples was measured with the BGA and a pH electrode (Hanna pH checker). The precision of both the BGA and the pH electrode were excellent (coefficient variation <1.4%). However, the closeness of agreement between measured values of both devices were not equivalent to each other in the tested IVF-media, showing 15% to 85% accordance between devices. The pH measured with the blood gas analyzer was also significantly higher in the tested media, compared to that measured by the pH electrode. One of the tested media did not reach its target pH when it was measured with the BGA, even at 9% CO2. The results show that the validated blood gas analyzer produces excellent results in terms of precision but not in terms of accuracy. Inaccurate measurement may lead to misinterpretation of results and consequently to suboptimal culture conditions. Therefore, each laboratory is encouraged to perform a validation of their BGA.

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