• Pregnancy
• Diagnostic & Surgical Procedures
• Infertility Clinical Trials

• Pregnancy
• Diagnostic & Surgical Procedures
• Infertility
• Obstetrics & Gynecology
• Obstetrics & Gynecology Clinical Trials

Jessica R. Kanter, BS, Emory University, Decatur, Georgia, USA, presented results from an 11-year study showing an increased incidence of monozygotic twin pregnancies over the past decade in association with the use of assisted reproductive technology (ART) [Kanter IR et al. Obstet Gynecol 2014]. Results also showed that Day 5 embryo transfer and assisted embryo hatching are associated with an increased risk of monozygotic twinning.

The use of ART has increased dramatically in recent decades, making pregnancy possible for many infertile couples. However, the use of ART has also been associated with a marked rise in the rate of multiple births in the United States, with the incidence of twin births almost doubling from 1971 through 2009 [Kulkarni AD et al. N Engl J Med 2013].

When compared with that of traditional fertility, monozygotic twinning is more common after infertility treatment; however, very little is known about the mechanisms involved or the factors contributing to its occurrence. Kanter and colleagues conducted a large population-based surveillance study to examine trends of monozygotic twinning in ART and to determine its association with transfer factors.

The study included 392 136 pregnancies resulting from fresh nondonor embryo transfers that were reported to the Centers for Disease Control and Prevention's National ART Surveillance System between 2000 and 2011.

Data were evaluated to examine trends of monozygotic twin pregnancies, defined as those in which the number of fetal heart tones on first-trimester ultrasound exceeded the number of embryos transferred. The results were subsequently compared with data for singleton pregnancies (1 fetal heart tone present) and other multiple-gestation pregnancies (>1 fetal heart tone present but not more than number of embryos transferred). Adjusted risk ratios (ARRs) were calculated for monozygotic twinning in association with assisted embryo hatching for singleton and other multiple-gestation pregnancies.

The results showed a significant increase in the incidence of monozygotic twinning after ART from 2000 through 2011 (p<0.001), with a higher incidence in Day 5 embryo transfers compared with Day 3 (1.72% vs 0.48%).

Monozygotic twinning was associated with assisted hatching among Day 3 embryo transfers with singleton pregnancies (ARR, 2.19; 95% CI, 1.93 to 2.48) and other multiple-gestation pregnancies (ARR, 2.27; 95% CI, 2.00 to 2.57) and among Day 5 embryo transfers when compared with other multiple-gestation pregnancies (ARR, 1.18; 95% CI, 1.05 to 1.32).

The results show an increased incidence of monozygotic twin pregnancies after ART over the past decade. They also show that Day 5 transfer and assisted hatching are associated with an increased risk of monozygotic twinning.

Kanter concluded that the rising incidence of monozygotic twinning in association with ART warrants a closer look. Prospective trials are still needed.

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