3.1 Population characteristics
In total, 5279 patients under 35 years old undergoing their first IVF / ICSI cycle with fresh, autologous embryos were subjected to analysis. Among the 5279 patients, 728 (13.79%) were considered underweight, 3650 (69.14%) normal-weight, 735 (13.92%) overweight, and 166 (3.14%) obese.
The general characteristics and biochemical test of all patients according to the BMI categories are detailed in Table 1. Compared with the normal-weight patients, the obese patients had the bigger body surface area (BSA), increased AFC and decreased baseline serum FSH, LH level, while the overweight patients had the older age, bigger BSA and decreased baseline serum FSH and LH level (P < 0.05). The underweight patients had the younger age, increased baseline serum FSH, LH level compared with the normal-weight (P < 0.05). There were no significant differences in the infertility duration, baseline serum testosterone, progestogen level of the patients among the BMI categories.
Table 1 Demographic data and biochemical tests of patients by BMI category
Variables
|
Underweight
(N = 728)
|
Normal-weight
(N = 3650)
|
Overweight
(N = 735)
|
Obesity
(N = 166)
|
Total
(N = 5279)
|
Years of infertility
|
3.64±2.23
|
3.83±2.48
|
4.01±2.66
|
4.65±2.76
|
3.85±2.49
|
Women’s age (year) ##
|
28.88±3.05*
|
29.75±2.88
|
30.34±2.78*
|
30.07±2.90
|
29.72±2.92
|
BMI (kg/m2) ##
|
17.62±0.70*
|
20.89±1.44
|
25.51±1.11*
|
30.13±2.22*
|
21.37±2.96
|
BSA (m2) ##
|
1.51±0.06*
|
1.61±0.08
|
1.75±0.09*
|
1.89±0.12*
|
1.62±0.11
|
Baseline FSH (U/L) ##
|
5.99±1.61*
|
5.59±1.78
|
5.18±1.40*
|
5.10±1.45*
|
5.57±1.71
|
Baseline LH (U/L) ##
|
4.11±1.82*
|
3.54±2.03
|
3.01±1.64*
|
2.85±1.80*
|
3.52±1.97
|
Baseline E2 (pmol/L) ## ########
|
150.07±70.87
|
139.79±120.40
|
123.06±99.12
|
130.98±83.04
|
138.61±111.12
|
Baseline T (nmol/L)
|
1.75±6.48
|
1.91±7.93
|
1.66±2.28
|
1.64±0.94
|
1.85±7.07
|
Baseline P (nmol/L)
|
1.60±5.03
|
1.15±2.72
|
1.02±1.45
|
0.83±0.42
|
1.18±2.98
|
AMH (ng/ml) #
|
3.99±3.06
|
3.89±2.69
|
3.55±2.52
|
3.62±2.60
|
3.84±2.72
|
AFC ##
|
14.56±4.39
|
15.30±4.92
|
16.05±5.51
|
18.25±6.38*
|
15.39±5.03
|
BMI = body mass index; BSA = body surface area; FSH = follicle stimulating hormone; LH = luteinizing hormone; E2 = estradiol; T = testosterone; P = progestogen; AMH = anti-Mullerian hormone; AFC = Antral follicle count;
Data are shown as the means ± standard;
#P < 0.05, ##P < 0.001, significantly different across the four BMI categories;
*P < 0.05, compared with normal-weight group.
3.2 IVF / ICSI treatment cycle characteristics
Regarding the response to the ovarian stimulation and cycle characteristics, we found that the overweight and obese women required more priming gonadotropin dose, total gonadotropin dose, administered dosage per unit of BSA and longer duration of stimulation compared with the patients with normal-weight (P < 0.05). On the other hand, we also found that the overweight and obese women had lower serum progestogen and estradiol on the day of HCG administration, lower increased of increase of E2, lower increase of E2 per unit of drug use and lower ovarian sensitivity index (OSI) compared with normal-weight patients (P < 0.05). In addition, requirement for less gonadotropin dose and shorter stimulation duration (P < 0.05) were found in the underweight infertile patients, with other variables were not significantly different (P > 0.05) (Table 2).
There were no significant differences in the number of oocyte retrieved, endometrial thickness on the day of HCG, high quality embryos rate, IVF-fertility rate, ICSI-fertility rate and the number of transferred embryos between the groups (Table 2).
Table 2 Characteristics of IVF / ICSI treatment by BMI category
Variable
|
Underweight
(N = 728)
|
Normal-weight
(N = 3650)
|
Overweight
(N = 735)
|
Obesity
(N = 166)
|
Total
(N = 5279)
|
Gonadotropin dose (IU)
|
|
|
|
|
|
Priming for cycle ##
|
154.81±48.95*
|
166.59±49.46
|
181.34±51.23*
|
191.42±54.32*
|
167.80±50.45
|
Total for cycle ##
|
2189.60±801.50*
|
2397.08±848.81
|
2779.17±933.81*
|
3118.22±1053.12*
|
2444.34±884.83
|
Duration of stimulation (days) ##
|
12.39±1.73
|
12.50±1.97
|
13.04±2.48*
|
13.28±2.65*
|
12.59±2.06
|
The day of HCG administration
|
|
|
|
|
|
P (nmol/L) ##
|
2.39±1.01
|
2.30±1.02
|
2.12±0.95*
|
1.93±0.83*
|
2.27±1.01
|
E2 (pmol/L) ##
|
11909.57±4097.27
|
11357.90±5293.88
|
9904.67±3879.56*
|
9223.48±4240.02*
|
11164.53±4978.45
|
Number of follicles > 16 mm in diameter#
|
3.50±3.76
|
3.88±3.95
|
4.05±4.01
|
4.04±4.09
|
3.86±3.94
|
Endometrial thickness (mm)
|
10.73±1.98
|
10.88±1.93
|
10.82±2.01
|
10.58±2.09
|
10.84±1.95
|
Administered dosage per unit BSA (IU/m²) ##
|
1452.05±531.63
|
1489.53±526.62
|
1588.73±530.46*
|
1650.48±541.71*
|
1503.23±530.25
|
The increased of E2 (pmol/L) ##
|
11939.69±4172.69
|
11354.88±5440.85
|
9819.43±3891.13*
|
8975.26±4301.26*
|
11152.27±5108.47
|
Increase of E2 per unit of drug use[(pmol/L)/IU] ##
|
6.39±3.56*
|
5.49±3.45
|
3.98±2.33*
|
3.32±2.19*
|
5.34±3.39
|
Number of oocytes retrieved
|
11.48±4.94
|
11.56±4.81
|
11.25±4.56
|
10.81±4.65
|
11.48±4.79
|
ovarian sensitivity index (OSI) ##
|
6.16±3.81*
|
5.63±3.44
|
4.59±2.69*
|
3.95±2.47*
|
5.50±3.41
|
High quality embryos (%)
|
45.10±29.65
|
43.66±29.87
|
43.87±28.77
|
41.38±28.84
|
43.82±29.66
|
IVF-fertility rate (%)
|
82.14±17.85
|
82.65±18.44
|
82.97±18.63
|
83.25±15.75
|
82.65±18.31
|
ICSI- fertility rate (%)
|
64.13±20.53
|
62.63±19.31
|
62.15±21.09
|
66.85±23.61
|
62.95±19.89
|
Number of transferred embryos
|
1.91±0.29
|
1.92±0.27
|
1.93±0.25
|
1.93±0.26
|
1.92±0.27
|
HCG = human chorionic gonadotropin; P = progestogen; E2 = estradiol; BSA = body surface area;
Data are shown as the means ± standard;
#P < 0.05, ##P < 0.001, significantly different across the four BMI categories;
*P < 0.05, compared with normal-weight group.
3.3 IVF / ICSI treatment outcomes
We analyzed the effects of BMI on pregnancy outcomes of IVF / ICSI. As shown in Table 3, the overweight and obese patients had the higher spontaneous abortion rate than normal-weight women (13.59% vs. 10.28%, OR = 1.40, 95% CI: 1.02 - 1,90, P = 0.036; 17.58% vs.10.28%, OR = 1.92, 95% CI: 1.09 - 3.36, P = 0.023, respectively), whereas underweight patients had a similar risk of spontaneous abortion. Compared with normal-weight patients, overweight and obese women seemed to have lower clinical pregnancy rate and live birth rate, but the difference was not statistically significant (P > 0.05).
Table 3 Pregnancy outcomes of IVF / ICSI treatment by BMI category
variable
|
Underweight
(N = 728)
|
Normal-weight
(N = 3650)
|
Overweight
(N = 735)
|
Obesity
(N = 166)
|
Clinical pregnancy rate
|
462(63.46%)
|
2227(61.01%)
|
434(59.05%)
|
91(54.82%)
|
OR (95% CI)a
|
1.14 (0.96,1.35)
|
Ref.
|
0.91 (0.77,1.07)
|
0.75 (0.55,1.04)
|
P-valuea
|
0.131
|
|
0.265
|
0.084
|
Spontaneous abortion rate
|
42(9.09%)
|
229(10.28%)
|
59(13.59%)#
|
16(17.58%)#
|
OR (95% CI)a
|
0.86 (0.61,1.22)
|
Ref.
|
1.40 (1.02,1.90)
|
1.92 (1.09,3.36)
|
P-valuea
|
0.398
|
|
0.036*
|
0.023*
|
Lived birth rate
|
345(47.39%)
|
1623(44.47%)
|
310(42.18%)
|
61(36.75%)
|
OR (95% CI)a
|
1.13 (0.96,1.34)
|
Ref.
|
0.92 (0.78,1.08)
|
0.73 (0.53,1.02)
|
P-valuea
|
0.129
|
|
0.305
|
0.063
|
#P < 0.05, compared with the normal-weight group;
a OR, P-values were from logistic regression analysis after adjusting age, duration of infertility, estradiol on HCG day, progesterone on HCG day, endometrial thickness on HCG day, number of oocytes retrieved, and number of embryos transferred, *P < 0.05.