Table 1.
Percentage Distribution of Patient and Cycle Characteristics in Monozygotic Twin Pregnancies and Singleton Pregnancies After Single Embryo Transfer, United States, 2003–2012
| Characteristic | Monozygotic Twin Pregnancies* (n=641) | Singleton Pregnancies† (n=27,955) | P |
|---|---|---|---|
| Maternal age (y) | .37 | ||
| Younger than 30 | 131 (20.4) | 5,258 (18.9) | |
| 30–34 | 288 (44.9) | 12,159 (43.5) | |
| 35–39 | 172 (26.8) | 8,352 (29.9) | |
| 40 or older | 50 (7.8) | 2,186 (7.8) | |
| Race or ethnicity | .61 | ||
| Non-Hispanic white | 284 (44.3) | 13,214 (47.3) | |
| Non-Hispanic black | 22 (3.4) | 951 (3.4) | |
| Asian or Pacific Islander | 55 (8.6) | 2,106 (7.5) | |
| Hispanic | 29 (4.5) | 1,186 (4.2) | |
| Other race | 0 | 39 (0.1) | |
| Unknown or missing | 251 (39.2) | 10,459 (37.4) | |
| Infertility diagnosis | |||
| Tubal factor | 75 (11.7) | 4,013 (14.4) | .06 |
| Endometriosis | 62 (9.7) | 2,752 (9.8) | .89 |
| Uterine factor | 21 (3.3) | 1,315 (4.7) | .09 |
| Ovulatory disorder (polycystic ovary syndrome) | 145 (22.6) | 5,212 (18.6) | .01 |
| Diminished ovarian reserve | 68 (10.6) | 3,745 (13.4) | .04 |
| Male factor | 219 (34.2) | 10,341 (37.0) | .14 |
| Unexplained | 100 (15.6) | 4,185 (15.0) | .66 |
| No. of prior pregnancies | .02 | ||
| 0 | 272 (42.5) | 13,181 (47.3) | |
| 1 or more | 368 (57.5) | 14,707 (52.7) | |
| No. of prior spontaneous abortions | .04 | ||
| 0 | 451 (70.4) | 20,678 (74.0) | |
| 1 or more | 190 (29.6) | 7,277 (26.0) | |
| No. of prior live births | 1.00 | ||
| 0 | 429 (67.0) | 18,674 (67.0) | |
| 1 or more | 211 (33.0) | 9,184 (33.0) | |
| No. of prior ART cycles | .99 | ||
| 0 | 441 (68.8) | 19,239 (68.8) | |
| 1 or more | 200 (31.2) | 8,715 (31.2) | |
| Day of transfer | <.001 | ||
| 2–3 | 162 (25.3) | 9,309 (33.3) | |
| 5–6 | 479 (74.7) | 18,646 (66.7) | |
| No. of oocytes retrieved | .07 | ||
| 1–4 | 91 (14.2) | 4,734 (16.9) | |
| 5 or more | 550 (85.8) | 23,221 (83.1) | |
| Use of ICSI | .02 | ||
| Did not use ICSI | 222 (34.8) | 8,540 (30.6) | |
| Used ICSI | 416 (65.2) | 19,366 (69.4) | |
| Use of assisted hatching | .46 | ||
| Did not use assisted hatching | 465 (72.5) | 20,639 (73.8) | |
| Used assisted hatching | 176 (27.5) | 7,316 (26.2) | |
| Supernumerary embryos available and cryopreserved | .21 | ||
| None | 271 (42.4) | 12,493 (44.9) | |
| 1 or more cryopreserved | 368 (57.6) | 15,342 (55.1) | |
ART, assisted reproductive technology; ICSI, intracytoplasmic sperm injection.
Data are n (%) unless otherwise specified.
Missing data less than 0.50% for all variables.
*
One embryo transferred and more than one fetal heart tone reported or more than one liveborn or stillborn neonate reported.
†
One embryo transferred and one fetal heart tone reported or one liveborn or stillborn neonate reported.