Table 2.
Relative Risk of Monozygotic Twinning by Cycle Characteristics for Day 2–3 Single-Embryo Transfers, 2003–2012
| Characteristic | Comparison Group: Singleton Pregnancies
|
||
|---|---|---|---|
| Monozygotic Twinning (%) | RR (95% CI) | Adjusted RR* (95% CI) | |
| Maternal age (y) | |||
| Younger than 30 | 2.2 | 1.64 (1.02–2.63) | 1.68 (1.05–2.71) |
| 30–34 | 1.3 | Reference | Reference |
| 35–39 | 2.0 | 1.46 (1.03–2.17) | 1.33 (0.90–1.97) |
| 40 or older | 1.6 | 1.18 (0.70–1.99) | 0.99 (0.56–1.76) |
| Infertility diagnosis | |||
| Tubal factor | 1.4 | 0.77 (0.48–1.22) | 0.68 (0.42–1.09) |
| Endometriosis | 1.9 | 1.13 (0.72–1.78) | 1.05 (0.66–1.67) |
| Uterine factor | 2.0 | 1.18 (0.60–2.29) | 1.14 (0.59–2.21) |
| Ovulatory disorder | 1.9 | 1.13 (0.74–1.74) | 1.05 (0.67–1.65) |
| Diminished ovarian reserve | 1.6 | 0.89 (0.62–1.29) | 0.77 (0.51–1.16) |
| Male factor | 1.5 | 0.83 (0.60–1.15) | 0.98 (0.68–1.42) |
| No. of prior pregnancies | |||
| 0 | 1.7 | Reference | Reference |
| 1 or more | 1.8 | 1.07 (0.79–1.46) | 1.15 (0.83–1.59) |
| No. of prior ART cycles | |||
| 0 | 1.8 | Reference | Reference |
| 1 or more | 1.5 | 0.84 (0.61–1.15) | 0.81 (0.58–1.13) |
| No. of oocytes retrieved | |||
| 1–4 | 1.9 | Reference | Reference |
| 5 or more | 1.6 | 0.85 (0.63–1.15) | 0.80 (0.56–1.13) |
| Use of ICSI | |||
| Did not use ICSI | 2.2 | Reference | Reference |
| Used ICSI | 1.5 | 0.69 (0.51–0.94) | 0.60 (0.42–0.85) |
| Use of assisted hatching | |||
| Did not use assisted hatching | 1.2 | Reference | Reference |
| Used assisted hatching | 2.3 | 1.81 (1.33–2.48) | 2.16 (1.53–3.06) |
| Supernumerary embryos available and cryopreserved | |||
| None | 1.7 | Reference | Reference |
| 1 or more cryopreserved | 1.7 | 1.00 (0.69–1.45) | 1.19 (0.78–1.82) |
RR, relative risk; CI, confidence interval; ART, assisted reproductive technology; ICSI, intracytoplasmic sperm injection.
*
Adjusted for all characteristics in the table.