IVF protocol
Women primarily underwent a GnRH antagonist protocol of treatment with vaginal progesterone gel (Crinone) / estradiol valterate luteal support or human-derived hCG luteal support (pregnyl) as previously described14. At the time of study (2009-2017) there were minimal changes to laboratory protocols including culture media, consumables or equipment used. Eggs were fertilised by either standard IVF or ICSI in fertilization medium (G-IVF-PLUS, Vitrolife, Gothenberg, Sweden). Embryos were cultured using the sequential culture media system supplied by Vitrolife at 6% CO2, 5% O2and 89% N2 where cleavage-stage embryos were grown until day 3 in G1 PLUS and then moved into G2 PLUS which supports blastocyst development until embryo transfer on day 4 or day 5. The best morphological graded embryo was transferred back into the patient using EmbryoGlue transfer medium (Vitrolife). Patients were in the care of their treating IVF physician until confirmation of a viable pregnancy following ultrasound at 6-8 weeks’ gestation, where they were then referred onto primary obstetrics care.