Table 1. Demographics and Cycle Characteristics of Recipientsa.
| Characteristics | Fresh embryo transfer (n = 15 308) | Cryopreserved-thawed embryo transfer (n = 36 634) |
|---|---|---|
| Age, y | n = 15 290 | n = 36 602 |
| Overall, median (IQR) | 42.0 (37.0-44.0) | 42.0 (36.0-45.0) |
| Age group, No. (%) | ||
| <35 | 2349 (15.4) | 7516 (20.5) |
| 35-37 | 1566 (10.2) | 3445 (9.4) |
| 38-40 | 2502 (16.4) | 4646 (12.7) |
| 41-42 | 2411 (15.8) | 4539 (12.4) |
| ≥43 | 6462 (42.3) | 16 456 (45.0) |
| Gravidity, median (IQR) | 1 (0-2) [n = 15 129] | 1 (0-3) [n = 34 622] |
| Parity, median (IQR) | 0 (0-1) [n = 8946] | 1 (0-1) [n = 25 320] |
| BMI | n = 11 321 | n = 22 365 |
| Overall, median (IQR) | 24.5 (21.9-28.7) | 24.4 (21.6-28.7) |
| Category, No. (%) | ||
| <18.5 | 235 (2.1) | 590 (2.6) |
| 18.5-24.9 | 5894 (52.1) | 11 608 (51.9) |
| 25-29.9 | 2946 (26.0) | 5744 (25.7) |
| 30.0-39.9 | 1976 (17.5) | 3891 (17.4) |
| ≥40 | 270 (2.4) | 532 (2.4) |
| Infertility diagnosis, No. (%)b | n = 15 308 | n = 36 634 |
| Diminished ovarian reserve | 11 722 (76.6) | 26 763 (73.1) |
| Male factor | 2556 (16.7) | 5302 (14.5) |
| Tubal factor | 965 (6.3) | 1967 (5.4) |
| Uterine factor | 853 (5.6) | 2729 (7.5) |
| Endometriosis | 793 (5.2) | 1709 (4.7) |
| Ovulatory | 385 (2.5) | 663 (1.8) |
| Unexplained | 663 (4.3) | 1392 (3.8) |
| Other | 2718 (17.8) | 9129 (24.9) |
| Gestational carrier, No. (%)c | 1133 (7.4) [n = 15 308] | 6624 (18.1) [n = 36 634] |
| Race/ethnicity, No. (%)d | n = 9831 | n = 22 367 |
| White | 6909 (70.3) | 14 852 (66.4) |
| Asian | 1318 (13.4) | 4333 (19.4) |
| Black/African American | 860 (8.7) | 1715 (7.7) |
| Hispanic/Latina | 703 (7.2) | 1347 (6.0) |
| Other | 41 (0.4) | 120 (0.5) |
| Day of transfer, No. (%)e | n = 14 071 | n = 28 622 |
| Day 3 | 1076 (7.7) | 1000 (3.5) |
| Day 3 and day 5/6 | 0 | 5 (0.02) |
| Day 5/6 | 12 995 (92.4) | 27 617 (96.5) |
| No. of embryos transferred, median (IQR) | 2 (1-2) [n = 15 308] | 1 (1-2) [n = 36 634] |
| Assisted hatching, No. (%)f | 3509 (22.9) [n = 15 301] | 25 701 (70.2) [n = 36 594] |
| Intracytoplasmic sperm injection, No. (%)g | 12 803 (83.6) [n = 15 308] | NA [n = 36 634] |
Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); IQR, interquartile range; NA, not available.
Percentages may not total to 100% on account of rounding.
Infertility diagnosis categories13 (multiple diagnoses can be made for 1 patient): “unexplained” includes patients who have completed an evaluation with no obvious explanation for their infertility; male factor refers to reduced sperm concentrations or other issues related to sperm function that make it difficult for a sperm to fertilize an oocyte under normal conditions; tubal factor refers to the fallopian tubes being blocked or damaged; ovulatory infertility refers to conditions in which the ovaries are not producing oocytes normally; infertility due to endometriosis is a medical condition that involves presence of tissue similar to the uterine lining in locations outside the uterus; diminished ovarian reserve refers to a reduced ability of the ovary to produce oocytes; uterine factor infertility refers to a structural or functional disorder of the uterus that results in reduced fertility; “other” incorporates diagnoses that do not meet criteria for any other category of infertility, such as women with a known chromosomal structural rearrangement or women with a history of malignancy that has led to infertility.
A gestational carrier is a woman who carries a pregnancy for intended parents when carrying a pregnancy is medically contraindicated or impossible for the intended mother.
Race and ethnicity categories were self-reported by patients to individual clinics. The category of “other” includes Native Hawaiian or other Pacific Islander, American Indian, and Alaska Native individuals as well as patients who reported “part” for their race/ethnicity.
Embryo transfer can occur at the cleavage stage of embryo development (day 3) or at the blastocyst stage of development (days 5/6). Rarely, a patient may have a transfer of a day 3 embryo followed by a transfer of a day 5/6 embryo. Pregnancy rates are higher with blastocyst transfer (day 5/6). Because only 30% to 50% of embryos develop into blastocysts, embryo transfer may be performed on day 3 for women with fewer available embryos to reduce the chance of cycle cancellation if no embryos survive to the blastocyst stage.
Assisted hatching involves creating a small opening in the zona pellucida to biopsy a blastocyst or to potentially facilitate implantation of a day 3 embryo. Within the time frame of the study, assisted hatching was commonly performed prior to transferring cryopreserved-thawed embryos.
The use of intracytoplasmic sperm injection, in which the sperm is directly injected into the oocyte for fertilization, was reported only in fresh embryo transfer cycles and was not available for cryopreserved-thawed embryo transfer cycles.