Characterization and risk factors for unexplained female infertility in Sudan: A case-control study

Table 1 Characterization of selected anthropometry and socio-demographic variables of study participants, n (%)

Variable	Categories	Cases (n = 210), N%	Control (n = 190), N%	Effect size Cramer’s V	P value
Age group (yr)	18-24	49 (23.3)	40(21.05)	0.083	0.61
	25-29	87 (41.4)	91(47.9)
	30-34	44 (21)	35(18.4)
	35-39	23 (11)	21(11.05)
	40-44	7 (3.3)	3(1.6)
	mean ± SD	28.59 ± 5.22	28.44 ± 4.95	NA	NA
BMI (kg/m2)	Underweight	1 (0.5)	4 (2.1)	0.073	0.53
	Normal weight	127 (60.5)	111 (58.4)
	Overweight	59 (28.1)	54 (28.4)
	Obesity	23 (10.9)	21 (11.1)
	mean ± SD	24.67 ± 4.08	24.41 ± 4.38	NA	NA
WHR	Less than 0.75	46 (22)	54 (28.4)	0.113	0.08
	075-0.84	53 (25.2)	35 (18.4)
	0.85-0.90	45 (21.4)	41 (21.6)
	Greater than 90	66 (31.4)	60 (31.6)
	mean ± SD	0.844 ± 0.108	0.837 ± 0.114	NA	NA
Residence	Rural	45 (21.4)	21 (11.1)	0.143	0.005
	Urban	165 (78.6)	169 (88.9)
Marital status	Married	208 (99.1)	170 (89.5)	0.214	0.001
	Divorced1	2 (0.9)	13 (6.8)
	Widow	0 (0)	7 (3.7)
Education status	Diploma or above	89 (42.4)	85 (44.7)	0.053	0.85
	Secondary edu	72 (34.3)	65 (34.2)
	Primary edu	39 (18.6)	34 (17.9)
	No formal edu2	10 (4.8)	6 (3.2)
Religious affiliation	Muslim	198 (94.3)	184 (96.8)	0.063	0.22
	Christian	12 (5.7)	6 (3.2)
Occupation	Farmer	9 (4.3)	2 (1.1)	0.164	0.06
	Governmental	34 (16.2)	29 (15.3)
	Housewife	132 (62.9)	110 (57.9)
	Private business	28 (13.3)	34 (17.9)
	NGOs	1 (0.5)	6 (3.2)
	Student	6 (2.9)	9 (4.7)

¹Information about, age, body mass index, and waist-to-hip ratio were reused from reference[81].

²Divorced women must have remained in regular sex in the last year intending to conceive.

³This includes the type of religious education (Khalwa). In the last column to the right, bold values indicate a significant level at P < 0.05. Cramer’s V effect size was classified according to Kim[41], 2017 as small effect size.

⁴Medium effect size. Differences between groups were compared with chi-square test. Estimated effect sizes were calculated using Cramer’s V statistic which is expressed as mean. Body mass index and waist-to-hip ratio status were follows World Health Organization and Centers for Disease Control and Prevention's classifications[36,37]. BMI: Body mass index; n: Sample size; NA: Not available; NGOs: Non-governmental organizations; SD: Standard deviation; WHR: Waist–hip ratio.

Table 2 History and clinical characteristics of study participants, n (%)

Variables	Categories	Cases (n = 210), N%	Controls (n = 190), N%	Effect size Cramer’s V	P value
Duration of infertility/marriage duration (yr)		Median = 3; Range = 1-15; IQR (3.75)	Median = 4; Range = 3-20; IQR (2)	NC	NC
Previous miscarriage or abortion	Yes	12 (5.71)	25 (13.16)	0.133	0.02
	No	198 (94.29)	165 (86.84)
Number of miscarriages or abortions	Never	198 (94.29)	165 (86.84)	0.164	0.08
	1	6 (2.86)	13 (6.84)
	2	4 (1.9)	6 (3.16)
	3	1 (0.48)	4 (2.1)
	4	0 (0)	2 (1.05)
	5	1 (0.48)	0 (0)
Family history of infertility	Yes	59 (28.1)	12 (6.3)	0.293	0.001
	No	151 (71.9)	178 (93.7)
Family history of Unexplained infertility	Yes	29 (13.8)	3 (1.6)	0.233	0.001
	No	181 (86.2)	187 (98.4)
Use of modern contraceptives/yr	Never	136 (64.8)	119 (62.6)	0.093	0.28
	0-3 yr	53 (25.2)	60 (31.6)
	4-6 yr	16 (7.6)	9 (4.7)
	More than 6 yr	5 (2.4)	2 (1.1)
	Not in use now	0 (0)	0 (0)
Alcohol consumption	Yes	0 (0)	0 (0)	NE	NE
	Not at all	210 (100)	190 (100)
	Stopped taking	0 (0)	0 (0)
Smoking1	Not at all	181 (86.2)	174 (91.6)	0.093	0.54
	< 1 yr	1 (0.48)	1 (0.53)
	1-2 yr	6 (2.9)	3 (1.6)
	2-3 yr	9 (4.3)	5 (2.6)
	> 4	13 (6.2)	7 (3.7)
Caffeine consumption (cup/d)2	No consume	8 (3.8)	6 (3.2)	0.063	0.72
	Low consume	68 (32.4)	69 (36.3)
	Moderate consume	66 (31.4)	51 (26.8)
	High consume	68 (32.4)	64 (33.7)
Physical activity level	Very active	43 (22.6)	38 (18.1)	0.083	0.26
	Moderately active	51 (26.9)	71 (33.8)
	Sedentary	96 (50.5)	101 (48.1)

¹The reported tobacco smoking in this study was in two forms [cigarettes, and shisha (water pipe)].

²Caffeine consumption was based only on liquid sources of caffeine (Tea, coffee, Sodas, and Energy Drinks).

³In the last column to the right, bold values indicate a significant level at P < 0.05. Cramer’s V effect size was classified according to Kim (2017)(41) as small effect size.

⁴Medium effect size.

Differences between groups were compared with chi-square test. Estimated effect sizes were calculated using Cramer’s V statistic which is expressed as mean. Physical activity level follows the WHO classification[38]. IQR: Interquartile range; n: Sample size; NC: Not Comparable due to dissimilar data; NE: Not evaluated in STATA due to zero value in one of the study groups.

Table 3 Frequency (Percentage) of dietary diversity and consumption patterns of different food groups by the study participants, n (%)

Variables	Categories	Cases (n = 210)	Controls (n = 190)	Effect size Cramer’s V	P value
Meals consumed per day	2	50 (23.8)	44 (23.2)	0.041	0.97
	3	89 (42.4)	86 (45.3)
	4	42 (20)	34 (17.9)
	5	24 (11.4)	21 (11.1)
	6	5 (2.4)	5 (2.6)
Grains, white roots, and tubers	No consume	0 (0)	0 (0)	NE	NE
	Low consume	0 (0)	0 (0)
	Moderate consume	0 (0)	0 (0)
	High consume	210 (100)	190 (100)
Pulses (beans, peas, and lentils)	No consume	7 (3.3)	4 (2.1)	0.091	0.36
	Low consume	27 (12.9)	36 (18.9)
	Moderate consume	51 (24.3)	43 (22.6)
	High consume	125 (59.5)	107 (56.3)
Nuts and seeds	No consume	57 (27.1)	69 (36.3)	0.111	0.18
	Low consume	88 (41.9)	77 (40.5)
	Moderate consume	37 (17.6)	25 (13.2)
	High consume	28 (13.3)	19 (10)
Dairy products	No consume	37 (17.6)	38 (20)	0.091	0.35
	Low consume	89 (42.4)	64 (33.7)
	Moderate consume	42 (20)	42 (22.1)
	High consume	42 (20)	46 (24.2)
Meat, poultry and fish	No consume	74 (35.2)	65 (34.2)	0.091	0.32
	Low consume	90 (42.9)	69 (36.3)
	Moderate consume	37 (17.6)	43 (22.6)
	High consume	9 (4.3)	13 (6.8)
Eggs	No consume	44 (20.9)	49 (25.8)	0.131	0.09
	Low consume	90 (42.9)	94 (49.8)
	Moderate consume	60 (28.6)	36 (18.9)
	High consume	16 (7.6)	11 (5.8)
Dark green leafy vegetables	No consume	16 (7.6)	13 (6.8)	0.021	0.97
	Low consume	101 (48.1)	89 (46.8)
	Moderate consume	55 (26.2)	53 (27.9)
	High consume	38 (18.1)	35 (18.4)
Other vitamin A-rich fruits and vegetables	No consume	25 (11.9)	25 (13.2)	0.081	0.47
	Low consume	87 (41.4)	75 (39.5)
	Moderate consume	63 (30)	48 (25.3)
	High consume	35 (16.7)	42 (22.1)
Other vegetables	No consume	26 (12.4)	33 (17.4)	0.081	0.49
	Low consume	83 (39.5)	66 (34.7)
	Moderate consume	57 (27.1)	49 (25.8)
	High consume	44 (20.9)	42 (22.1)
Other fruits	No consume	28 (13.3)	30 (15.8)	0.041	0.88
	Low consume	94 (44.8)	84 (44.2)
	Moderate consume	56 (26.7)	46 (24.2)
	High consume	32 (15.2)	30 (15.8)

¹The significance level was set at P < 0.05. Cramer’s V effect size was classified according to Kim[41], 2017, as small effect size. Differences between groups were compared with chi-square test. Estimated effect sizes were calculated using Cramer’s V statistic which is expressed as mean. The four classifications of the consumption levels of the different food groups per week followed FAO classifications[27]. n: Sample size; NE: Not evaluated in STATA due to zero value in one of the study groups.

Table 4 Binary logistic regression analysis of the factors associated with unexplained female infertility in the study participants

Predictors	COR, 95%CI	AOR, 95%CI
Residence
Urban	Reference	Reference
Rural	2.195 (0.225-1.347)a	1.996 (-0.165-1.548)
Marital status
Married	Reference	Reference
Divorced	0.126 (-3.576-0.571)a	0.073 (-4.431-0.803)a
Widow	0.419 (-0.922-0.386)a
Previous miscarriage or abortion
No	Reference	Reference
Yes	0.4 (-1.635 - 0.198)a	0.426 (-1.874-0.165)
Family history of infertility
No	Reference	Reference
Yes	5.796 (1.1 - 2.415)a	3.257 (0.175-2.186)a
Family history of Unexplained infertility
No	Reference	Reference
Yes	9.987 (1.095- 3.507)a	3.580 (-0.594-3.145)
Use of modern contraceptives/yr
Never	Reference	Reference
0-3 yr	0.188 (-2.147-1.191)a
4-6 yr	0.052 (-4.446-1.477)a	0.475 (-0.987-0.502)a
More than 6 yr	0.085 (-0.484-0.823)
Smoking
Not at all	Reference	Reference
< 1 yr	1.751 (-0.077-2.434)a
1-2 yr	2.983 (-0.251-2.437)a	1.276 (0.010-0.476)a
2-3 yr	4.102 (0.117-2.706)a
> 4	3.356 (0.176-2.245)a
Caffeine consumption (cup/d)
No consume	Reference	Reference
Low consume	0.254 (-2.521-0.219)a
Moderate consume	0.648 (-1.586-0.718)a	0.407 (0.168-0.514)a
High consume	0.426 (-0.802-1.512)a
Physical activity level (PAL)
Sedentary	Reference	Reference
Moderately active	0.237 (-1.394- 0.464)a	0.423 (-1.240-0.481)a
Very active	0.292 (-2.291- 1.145)a
Meals consumed per d
2	Reference	Reference
3	4.172 (0.876-1.981)a
4	5.293 (1.006-2.326)a	1.606 (0.169-0.778)a
5	5.286 (0.899-2.432)a
6	2.917 (-0.253-2.394)
Dairy
No consume	Reference	Reference
Low consume	1.551 (-0.118-0.997)a
Moderate consume	0.974 (-0.649-0.596)a	0.777 (-0.540-0.036)
High consume	0.674 (-1.015-0.226)a
Dark green leafy vegetables
No consume	Reference	Reference
Low consume	1.014 (-0.780-0.807)a
Moderate consume	0.789 (-1.067-0.593)a	0.730 (-0.651-0.021)
High consume	0.346 (-1.948-0.176)a
Other vitamin A-rich fruits and vegetables
No consume	Reference	Reference
Low consume	0.673 (-1.078-0.287)a
Moderate consume	0.469 (-1.467-0.047)a	0.540 (-0.948-0.283)a
High consume	0.131 (-2.837-1.232)a
Other vegetables
No consume	Reference	Reference
Low consume	0.177 (-2.543-0.920)a
Moderate consume	0.169 (-2.614-0.940)a	0.466 (-1.087-0.441)a
High consume	0.064 (-3.623-1.866)a

^aIndicates a statistically significant effect at P < 0.05. Identification of female unexplained infertility predictors among clinical characteristics was done using a univariate and multivariate logistic regression analysis test. AOR: Adjusted odds ratio; CI: Confidence interval; COR: Crude odds ratio; n: Sample size.