A comparison of biochemical pregnancy rates between women who underwent IVF and fertile controls who conceived spontaneously

STUDY QUESTION: Does IVF affect the biochemical pregnancy rate? SUMMARY ANSWER: The likelihood of an early pregnancy loss may be lower and is certainly not higher in IVF cycles when compared with published rates of biochemical pregnancy in fertile women <= 42 years old. WHAT IS KNOWN ALREADY: The use of gonadotrophins to stimulate multi-folliculogenesis alters endometrial expression of genes and proteins, compared with unstimulated cycles. Exogenous estrogen and progesterone taken for endometrial preparation in frozen embryo transfer cycles, also cause changes in endometrial gene and protein expression. These endometrial alterations may compromise the ability of embryos to develop once implanted, possibly increasing the biochemical pregnancy rate. STUDY DESIGN, SIZE, DURATION: This is a retrospective study, involving 1636 fresh and 188 frozen, single embryo transfer (SET) IVF cycles performed between August 2008 and December 2012. The biochemical pregnancy rate of the 1824 combined IVF and frozen cycles were compared with fertile controls, derived from the three prospective studies in the medical literature that evaluate this rate. PARTICIPANTS/MATERIALS, SETTING, METHODS: Subjects <= 42-years old, who underwent a SET, as part of a fresh or thawed IVF cycle were considered for inclusion. Each subject is represented only once. The biochemical pregnancy rates were compared with those of historical standard, fertile populations with spontaneous conceptions. MAIN RESULTS AND THE ROLE OF CHANCE: The pregnancy rates per transfer for fresh and frozen IVF cycles were similar at 39 and 40%, respectively. There was also no significant difference in the likelihood of pregnancy outcomes (clinical, biochemical and ectopic pregnancy) between fresh IVF and frozen cycles (85.4 versus 85.6%, 13.8 versus 14.8%, 0.5 versus 0%, P = 0.82). However, pregnancy rates decreased in older patients when compared with younger ones P < 0.0001. The biochemical pregnancy rate for fresh and frozen IVF cycles combined was 13.8% of all pregnancies. IVF and frozen cycles were combined as the IVF group treated with hormones for further comparison with the fertile control group. The biochemical pregnancy rate (14%) in the IVF group was lower than the rate based on the total fertile group (18%), P = 0.01 and differed significantly from the rate in two out of the three studies used to establish the normative rate. The age ranges of the IVF and fertile controls were 21-42 years. The mean age in the IVF population was 34.8 years, as compared with 29 years, 29, 4 years and 30.6 years (Zinaman) in the three published studies (mean: 29.4 years). LIMITATIONS, REASONS FOR CAUTION: This is a retrospective study and it was impossible to recruit an in-house biochemical pregnancy control population. WIDER IMPLICATIONS OF THE FINDINGS: Lower early pregnancy wastage after IVF may be due to the opportunity to select the embryo for transfer. This finding should be confirmed in further studies but supports the idea that embryo selection is an important step.