Split happens: a case of consecutive monozygotic twin pregnancies following elective single-embryo transfer in a 40-year old woman using donor oocytes

Excerpt

Monozygotic twins derive from a single zygote that undergoes division at varying stages of development, the timing of which ultimately determines placental sharing. Morula stage (days 1–4) division results in dichorionic-diamniotic twins that cannot be differentiated from dizygotic twins in utero. Blastocyst stage (days 4–8) division results in monochorionic-diamniotic twins. Division at the 8–12-day stage results in monochorionic-monoamniotic twins, and division after day 12 leads to conjoined twins [1, 2]. Monozygotic twinning is seen at a rate of 0.4% in natural conceptions, though that rate is significantly higher, ranging from 1.57–5.6%, when blastocysts are transferred using assisted reproductive technologies (ART) [3‐5]. Although consensus has not been reached in the literature, it is thought that factors such as intracytoplasmic sperm injection (ICSI), blastocyst transfer, assisted hatching (AH), and individual embryologist technique may play a role in the increased frequency of monozygotic twinning in ART [2, 6]. It is widely agreed upon, however, that monozygotic twins carry a greater risk of adverse outcomes such as premature delivery, growth discordance, developmental abnormalities, and perinatal mortality when compared to singleton or dizygotic pregnancies [5]. …