Background: Blastocyst culture and elective single embryo transfer programmes are increasingly used to reduce multiple pregnancies after IVF. To optimize the results, there is a need to better select embryos, to implement efficient cryopreservation programmes and to refine selection criteria. In the present study, we set out to identify relevant clinical predictors of healthy term birth (HTB) after single blastocyst transfer (SBT).
Design: analysis of prospectively collected database.
Setting: University IVF centre in Nantes, France. In 872 infertile women undergoing their first IVF cycle with SBT between January 2007 and December 2008, multivariable analysis and logistic regression were used to identify predictive factors of HTB, i.e. delivery of a live born term singleton of ≥ 2500 g, surviving at least 28 days with no reported congenital anomaly.
Results: Of 304 deliveries, there were 16 twin pairs (5.5%) and no high order deliveries. The rate of HTB was 266/872 (30.5%). Univariate analysis showed that the probability of HTB was significantly higher in women under 35 years [odds ratio (OR):1.75, 0.95 confidence interval (CI): 1.2-2.5, P = 0.001], in women with a BMI < 30 kg/m² (OR: 3.0, 0.95 CI: 1.5-5.9, P = 0.001), in non-smoking women (OR: 2.2, 0.95 CI: 1.5-3.2, P < 0.0001), and after Day 5 compared with after Day 6 transfer (OR: 2.65, 0.95 CI: 1.8-3.8, P < 0.0001). Multivariable analysis showed that BMI, smoking and day of embryo transfer were independent predictors of HTB, regardless of female age.
Conclusions: After SBT, female obesity and smoking reduce the chance of HTB, independent of female age. Day 6 transfer should be avoided.