Dizygotic twin pregnancy after single embryo transfer: a case report and review of the literature

IntroductionElective single embryo transfer (SET) is a reasonable optionfor avoiding multiple pregnancies in patients who undergoassisted reproductive technology (ART) treatment [1, 2]. TheJapan Society of Obstetrics and Gynecology (JSOG) recom-mends SET for patients under 35 years of age and for thosewho have undergone ≤2 treatment cycles since 2008. TheJSOG recommendation increased the use of the SET tech-nique from 49.9 % (52,800/105,812) of all embryo transfercyclesin2007to73%(106,758/146,286)in2010[3,4].Asaresult, the proportion of all embryo transfer cycles that result-ed in multiple pregnancies decreased from 3.0 % in 2007 to1.3 % in 2010 [3, 4].Multiplepregnancies may occur evenifSETisperformed.Todate,17casesinvolvingtwinortripletpregnanciesaftertheSEThavebeenreported[5].Inthe general population,mono-zygotic twins have been calculated to account for 0.4–0.45 %ofalllivebirths[6,7].InpatientsundergoingART,thisrateisapproximately twice that of spontaneous pregnancies [8, 9].Theoretically,twinsresultingfromaSETprocedureshouldbemonozygotic.However,areviewoftheliteraturesuggeststhat4 cases of dizygotic twin pregnancies have been reported inpatients undergoing the SET technique [10–12]. Here, wepresent a fifth case and a review of the literature concerningthis phenomenon.Case reportA 39-year-old, nulligravida woman and her 44-year-old hus-band had an 8-year history of infertility. She had regular men-strual cycles occurring every 28 days and lasting 7 days, andwas negative for Chlamydia trachomatis IgAandIgGantibod-ies. She had bilateral tubal patency by hysterosalpingography.Her husband’s semen analysis showed normozoospermia,based on the 2010 World Health Organization criteria.The woman underwent in vitro fertilization (IVF) and em-bryo transfer with a long-protocol, gonadotropin-releasing hor-mone agonist because of unexplained infertility. Nine cumulusoocytecomplexes(COCs)wereaspiratedandtheseCOCsweresubjected to IVF. Six fertilized oocytes with two pronuclei wereobserved 20 h after insemination. Although one embryo at themorulastagewastransferredtotheuterusondayfourafterIVF,she did not become pregnant. The remaining four morula-stageembryos with good morphology were subjected to vitrificationin a solution containing 40 % (v ol/vol) ethylene glycol, 18 %(wt/vol) Ficoll 70, and 0.3 mol/L trehalose [ 13]. After 2 monthsof IVF treatment, the patient became pregnant spontaneously,but this resulted in a biochemical pregnancy. Four months aftervitrification of the embryos, four embryos were warmed for ascheduled embryo transfer, according to the patient ’snaturalmenstrual cycle. Ovulation was confirmed by follicular moni-toringwithtransvaginalultrasonographyonday17ofthecycle.The embryo transfer was planned 5 days after the ovulation.Warmingofmorula-stageembryoswasperformedonthedaybefore the scheduled embryo transfer. Three surviving morula-stage embryos were cultured, a fter warming in Global Medium(LifeGlobal, Gilford, CT, USA) supplemented with 10 % syn-thetic serum substitute (Irvine Scientific, Santa Ana, CA, USA)for 18 h. One embryo showed further development and reachedthe expanded blastocyst stage. The expanded blastocyst wastransferred into the patient’s uterus. Ten days after embryotransfer, her pregnancy test was positive. Two gestational sacswith fetal heart beats in each gestational sac were observed by