A modified natural cycle results in higher live birth rate in vitrified-thawed embryo transfer for women with regular menstruation

Figures & data

Table 1. Patient demographics in different frozen-thawed embryo transfer (FET) cycles and FET cycle characteristics.

Characteristic	Total (1,482)	Group NC (n=427)	Group OC (n=132)	Group AC (n=794)	Group GAC (n=129)	P
Baseline parameters
Age (y)	31.5 ± 5.3	31.2 ± 5.0	32.2 ± 5.3	31.3 ± 5.2	33.8 ± 5.2^a	<0.01
Basal FSH (IU/L)	6.8 ± 4.5	6.7 ± 2.5	7.0 ± 3.2	6.9 ± 5.5	6.9 ± 3.8	0.837
Basal LH (IU/L)	5.0 ± 4.5	4.5 ± 2.7	4.9 ± 2.9	5.2 ± 5.4	5.3 ± 4.6	0.071
Body Mass Index (BMI) (kg/m^2)	22.4 ± 3.1	22.1 ± 2.3	22.3 ± 2.9	22.5 ± 2.9^b	22.1 ± 2.3	<0.01
Duration of Infertility (y)	4.3 ± 3.3	4.1 ± 3.2	4.5 ± 4.0	4.3 ± 3.3	4.7 ± 3.1	0.291
Indication for treatment
Male Factor (%)	315 (21.8)	109 (25.5)	18 (13.6)	166 (20.9)	27 (21.0)
Female Factor (%)	787 (54.4)	220 (51.5)	75 (56.8)	429 (54.0)	83 (64.3)
Both Factor (%)	302 (20.9)	84 (19.7)	30 (22.7)	180 (22.7)	16 (12.4)
Unknown Factor (%)	43 (3.0)	14 (3.3)	9 (6.8)	19 (2.4)	3 (2.3)
FET characteristics
Embryos Transferred (n)	2.4 ± 0.6	2.2 ± 0.6	2.2 ± 0.6	2.2 ± 0.6	2.4 ± 0.6	0.076
Top Quality Embryos (%)	231 (16.0)	67 (15.7)	21 (15.9)	133 (16.8)	17 (13.2)	0.772
Endometrial Thickness (mm)	9.5 ± 1.7	10.0 ± 1.7^c	9.3 ± 1.8	9.2 ± 1.5	9.9 ± 2.4^d	<0.01

Group NC: modified natural cycles; Group OC: ovulation induction cycles; Group AC: artificial cycles; Group GAC: GnRH agonist artificial cycles. Values are mean (± SD) or number (%). ^aStatistically significant, compared with NC, AC (P=0.000). ^bStatistically significant, compared with NC (P=0.000). ^cStatistically significant, compared with OC, AC (P=0.000). ^dStatistically significant, compared with AC (P=0.000).

Table 2. The pregnancy outcomes in different frozen-thawed embryo transfer (FET) cycles.

Characteristic	Total (1,482)	Group NC (n=427)	Group OC (n=132)	Group AC (n=794)	Group GAC (n=129)	P
General clinical data
Implantation rate (%)	29.0 (918/3,296)	31.9^a (303/950)	25.8 (75/291)	27.1 (474/1752)	25.1 (76/303)	<0.01
Clinical pregnancy rate (%)	677 (45.7)	215 (50.4)	54 (40.9)	351 (44.2)	57 (44.2)	0.123
Ongoing pregnancy rate (%)	546 (36.8)	187 (43.8)^b	44 (33.3)	276 (34.8)	39 (30.2)	<0.01
Loss of Pregnancy
Early abortion rate (%)	12.1 (82/677)	9.8 (21/215)	14.8 (8/54)	12.8 (45/351)	14.0 (8/57)	0.605
Late abortion rate (%)	5.3 (36/677)	2.8 (6/215)	3.7 (2/54)	5.7 (20/351)	14.0^c (8/57)	<0.01
Ectopic pregnancy rate (%)	2.5 (16/677)	0.5 (1/215)	3.7 (2/54)	3.4 (12/351)	3.5 (2/57)	0.059
Pregnancy Complications
Hypertensive disorders rate (%)	5.6 (38/677)	6.0 (13/215)	7.4 (4/54)	5.7 (20/351)	1.8 (1/57)	0.561
Placental vascular disease rate (%)	1.5 (10/677)	0.9 (2/215)	0.0 (0/54)	2.0 (7/351)	1.8 (1/57)	0.647
Gestational diabetes rate (%)	1.9 (10/677)	2.3 (5/215)	5.6 (3/54)	1.4 (5/351)	0.0 (0/57)	0.159

Group NC: modified natural cycles; Group OC: ovulation induction cycles; Group AC: artificial cycles; Group GAC: GnRH agonist artificial cycles. Note: Values are mean (± SD) or number (%). ^aStatistically significant, compared with AC (P=0.008). ^bStatistically significant, compared with AC (P=0.002) and ^bstatistically significant, compared with GAC (P=0.006). ^cStatistically significant, compared with NC (P=0.003).

Table 3. The perinatal and neonatal outcomes in different frozen-thawed embryo transfer (FET) cycles.

Characteristic	Total (1,482)	Group NC (n=427)	Group OC (n=132)	Group AC (n=794)	Group GAC (n=129)	P
Perinatal data
Premature delivery rate (%)	22.2 (119/536)	21.2 (39/184)	16.7 (7/42)	22.1 (60/271)	33.3 (13/39)	0.319
Term delivery rate (%)	76.3 (409/536)	77.7 (143/184)	83.3 (35/42)	76.6 (208/271)	59.0 (23/39)	0.049
Post-term delivery rate (%)	1.5 (8/536)	1.1 (2/184)	0.0 (0/42)	1.1 (3/271)	7.7 (3/39)	0.062
Live birth rate (%)	536 (36.2)	184 (43.1)^a	42 (31.8)	271 (34.1)	39 (30.2)	<0.01
Intrauterine growth retardation rate (%)	20.2 (141/699)	22.6 (55/243)	10.0 (5/50)	18.5 (66/356)	30.0 (15/50)	0.051
Fetal macrosomia rate (%)	7.9 (55/699)	9.9 (24/243)	6.0 (3/50)	7.6 (27/356)	2.0 (1/50)	0.275
Neonatal data
Mean birth weight (g)	3005.3 ± 693.8	2969.4 ± 731.9	3118.4 ± 651.6	3030.6 ± 659.9	2887.0 ± 770.6	0.272
Stillborn rate (%)	0.9 (6/677)	1.4 (3/215)	0.0 (0/54)	0.9 (3/351)	0.0 (0/57)	0.891
Neonatal mortality rate (%)	0.7 (5/699)	0.4 (1/243)	2.0 (1/50)	0.6 (2/356)	2.0 (1/50)	0.215
Birth defects rate (%)	0.7 (5/699)	0.8 (2/243)	0.0 (0/50)	0.8 (3/356)	0.0 (0/50)	1.000
Cerebal palsy rate in singletons (%)	1.3 (5/375)	1.6 (2/127)	0.0 (0/34)	1.6 (3/186)	0.0 (0/28)	1.000

Group NC: modified natural cycles; Group OC: ovulation induction cycles; Group AC: artificial cycles; Group GAC: GnRH agonist artificial cycles. Values are mean (± SD) or number (%). ^aStatistically significant, compared with AC, (P=0.002).

Table 4. Multivariate logistic regression analysis for live birth rate.

Independent variable	B	Wald statistic	P	OR	(95% CI)
Age (y)	0.003	0.099	0.753	1.003	0.983-1.024
Basal FSH (IU/L)	−0.018.	1.027	0.311	0.982	0.947-1.017
Body mass index (kg/m^2)	−.0.007	0.149	0.699	0.993	0.959-1.029
Duration of infertility (y)	−0.086	20.880	0.000	0.918	0.885-0.952
Embryos transferred (n)	0.313	10.333	0.001	1.367	1.130-1.654
Endometrial thickness (mm)	0.099	9.345	0.002	1.104	1.036-1.176
Protocols
NC			Reference group
OC	−0.352	2.683	0.101	0.703	0.462-1.072
AC	−0.283	4.884	0.027	0.753	0.586-0.968
GAC	−0.547	6.123	0.013	0.579	0.375-0.892

OR: odds ratio; CI: confidence interval; Group NC: modified natural cycles; Group OC: ovulation induction cycles; Group AC: artificial cycles; Group GAC: GnRH agonist artificial cycles.