Monozygotic twinning associated with assisted reproductive technologies: a review

Abstract

Twin birth rates have increased markedly in developed countries since the 1970s for two primary reasons: increasing maternal age and the advent and increasing use of fertility treatments. In addition, monozygotic (MZ) twin pregnancies have been reported to occur at a significantly higher rate following assisted reproductive technologies (ART) procedures compared with the natural incidence. Twin pregnancies are of concern due to a dramatically increased risk of associated complications. Monozygotic twin pregnancies carry a 10-20% risk of twin-twin transfusion syndrome, and monoamniotic monochorionic twins are additionally at risk for cord entanglement. While the mechanisms and contributory factors for dizygotic twinning are well established, very little is known about the mechanisms involved in MZ twinning or the factors that contribute to its occurrence. In this review, we will discuss a number of potential mechanisms involved in MZ twinning and explore factors that may be contributing to the increased incidence of ART-associated MZ twins. An improved understanding of the factors that contribute to increased MZ twinning associated with ART will help to elucidate the poorly understood mechanisms involved in the process and will further aid in reducing the overall incidence of multiple pregnancies with their associated risks following ART procedures.

Clustering of monozygotic twinning in IVF

“…Current evidence suggests that multiple factors might be responsible, including maternal age, ovarian stimulation, prolonged embryo culture, altered in vitro culture conditions, and zona pellucida manipulation [11]. However, a meta-analysis and a recent large study did not show an association between intracytoplasmic sperm injection (ICSI) or assisted hatching and MZT [9,12].…”

“…However, a meta-analysis and a recent large study did not show an association between intracytoplasmic sperm injection (ICSI) or assisted hatching and MZT [9,12]. Blastocyst culture appears to be one of the most important factors contributing to MZ pregnancies [10,11]. Knopman et al [13] noted increased MZT rates among younger women when the maternal age of oocytes was <35 years; however, these results are confounded by the fact that younger women were more likely to have embryos transferred at the blastocyst stage [13].…”

First-trimester diagnosis of conjoined twins in a multifetal pregnancy after assisted reproduction technique using HDlive rendering

“…Currently, assisted reproduction techniques (ART) are widely used to treat infertility and have increased the number of multiple pregnancies, consequently increasing maternal, fetal, and neonatal risks, in relation to the number of fetuses [1]. The incidence of monozygotic twin (MZT) pregnancy following ART is believed to range between two-and 12-fold the natural occurrence of 0.4% [1].…”

“…The incidence of monozygotic twin (MZT) pregnancy following ART is believed to range between two-and 12-fold the natural occurrence of 0.4% [1]. Conjoined twins (CT) are a rare complication of MZT pregnancies with an estimated 1 case per 1,00,000-2,00,000 spontaneous pregnancies and in 1% of MZT pregnancies.…”

“…ART has become popular for the treatment of infertility worldwide; consequently, the incidence of MZT has increased [1]. First-trimester screening and intense surveillance in early pregnancy after ART have made the diagnosis of CT more common during the first trimester.…”