TABLE 4.

Risk of first trimester pregnancy loss among pregnancies after transfer of frozen versus fresh embryos, stratified by maternal age at oocyte retrieval, subgroup analysis.

	Fresh embryos	Frozen embryos
Maternal age (y)	First trimester losses, n (%)	First trimester losses, n (%)	RR (95% CI)a	aRR (95% CI)a
<30	2,729 (8.2)	199 (12.0)	1.46 (1.26–1.69)	1.16 (1.04–1.32)
30–34	7,687 (10.0)	396 (13.1)	1.31 (1.17–1.47)	1.08 (0.98–1.18)
35–37	6,286 (13.7)	271 (16.3)	1.19 (1.06–1.33)	1.07 (0.96–1.18)
38–40	7,337 (21.5)	240 (21.6)	1.00 (0.88–1.14)	0.96 (0.87–1.05)
>40	5,160 (37.1)	136 (32.2)	0.87 (0.74–1.02)	0.89 (0.79–0.99)

Note: Frozen cycles restricted to those occurring directly after a fresh cycle during which no transfer was performed (i.e., first ET from originating fresh cycle). Models were adjusted for number of prior miscarriages, prior births, and prior ART cycles, the infertility diagnoses of ovulatory dysfunction, DOR, and uterine factor, number of oocytes retrieved, number of embryos transferred, the use of assisted hatching, and the number of fetal heartbeats on first ultrasound. aRR = adjusted risk ratio; ART = assisted reproductive technology; CI = confidence interval; DOR = diminished ovarian reserve; RR = risk ratio.

^aReference group is fresh ET.