Effect of blastocyst morphology on the incidence of monozygotic twinning pregnancy after single blastocyst transfer

Figures & data

Figure 1. Flowchart of the retrospective cohort study. Note: SBT = single blastocyst transfer; GS = gestational sac; FHB = fetal heartbeat; No. = number of.; IVF = in vitro fertilization; ICSI = intracytoplasmic sperm injection; ET = embryo transfer; PGD = preimplantation genetic diagnosis.

Table 1. Demographic characteristics of patients and embryos in the MZT and singleton cohorts of single blastocyst transfer cycles.

Variable	MZT (n, %)	Singleton (n, %)	p value
No. of cycles	227 (2.46)	9,002 (97.54)
Maternal age (year)	29.99 ± 3.67	30.26 ± 4.23	.272
<25	12 (1.72)	686 (7.62)	.100
25–29	90 (2.63)	3,375 (37.49)
30–34	99 (2.75)	3,499 (38.87)
35–39	25 (1.99)	1,232 (13.69)
≥40	1 (0.47)	210 (2.33)
BMI (kg/m^2)	22.92 ± 3.11	23.28 ± 3.34	.114
Basal FSH (U/L)	6.36 ± 1.93	6.31 ± 1.81	.683
Ovarian stimulation Protocol* (n)			.173
GnRH agonist	106 (2.73)	3,781 (98.77)
GnRH antagonist	2 (5.26)	36 (0.94)
Mid-stimulation	1 (0.23)	11 (0.29)
Insemination method* (n, %)			.061
Conventional IVF	93 (3.03)	2,978 (77.80)
ICSI	16(1.85)	850 (22.20)
AH (n, %)			.172
No	95 (2.74)	3,367 (37.40)
Yes	132 (2.29)	5,635 (62.60)
Type of ET (n, %)			.098
Fresh	109 (2.77)	3,828 (42.52)
Frozen-thawed	118 (2.23)	5,174 (57.48)
In vitro culture time (n, %)			.040
Day 5	205 (2.60)	7,692 (85.45)
Day 6	22 (1.65)	1,310 (14.55)
Blastocyst stage (n, %)			.589
1	0	4 (0.04)
2	2 (2.78)	70 (0.78)
3	62 (2.14)	2,836 (31.50)
4	154 (2.60)	5,772 (64.12)
5	8 (3.24)	239 (2.65)
6	1 (1.22)	81 (0.90)
Inner cell mass grading (n, %)			.038
A	82 (2.97)	2,677 (29.74)
B	145 (2.24)	6,325 (70.26)
Trophectoderm grading (n, %)			.002
A	32 (3.40)	910 (10.11)
B	157 (2.67)	5,732 (63.67)
C	38 (1.58)	2,360 (26.22)
Endometrial preparation protocols^# (n, %)			.520
NC	44 (2.41)	1,782 (34.44)
HRT	74 (2.14)	3,392 (65.56)

Note: Data are presented as mean ± standard deviation or number (percentage), unless otherwise indicated. BMI = body mass index; FSH = follicle-stimulating hormone; GnRH = gonadotropin-releasing hormone; IVF = in vitro fertilization; ICSI = intracytoplasmic sperm injection; ET = embryo transfer; NC = natural cycle; HRT = hormone replacement therapy; MZT = monozygotic twinning.

* Only of fresh ET.

^# Only of frozen-thawed ET.

Figure 2. Key factors affecting the frequency of MZT. ‘aOR’ indicates that the odds ratio (or) and 95% CI were adjusted for potential confounding factors. Note: MZT = monozygotic twinning; ICM = inner cell mass; TE = trophectoderm; AH = assisted hatching.

Figure 3. MZT rate of different ICM and TE grading of blastocysts based on the Gardner scoring system. Note: ICM = inner cell mass; TE = trophectoderm; MZT = monozygotic twinning.

Table 2. Multivariate analysis of the blastocyst morphology parameters on MZT.

Variable	aOR	95%CI	p value
Maternal age	0.988	0.953–1.024	.501
Type of ET
Fresh	ref
Frozen-thawed	0.786	0.424–1.457	.445
In vitro culture time
Day 5	1.281	0.787–2.087	.319
Day 6	ref
AH
Yes	1.201	0.630–2.287	.578
No	ref
Blastocyst stage
1 + 2	ref
3 + 4	0.889	0.216–3.666	.871
5 + 6	1.125	0.235–5.385	.883
ICM grading
A	1.057	0.764–1.463	.737
B	ref
TE grading
A	1.883	1.069–3.315	.028
B	1.559	1.066–2.279	.022
C	ref

Note: AH = assist hatching; ICM = Inner cell mass; TE = trophectoderm; aOR = adjust odds ratio; CI = confidence interval; ref = reference.