Table 2. Review of the studies and results. The relationship between obesity and high body mass index and pregnancy loss.

BMI: body mass index; CI: confidence interval

Zhou et al. [21]	A prospective cohort analysis	data from a 2006 to 2009	18,481 Chinese nulliparous women	Obesity was defined as BMI ≥ 27.5 kg/m2	Results:  fetal loss (ARR 1.51; 95% CI: 1.15-1.99  spontaneous abortion (ARR 1.51; 95% CI: 1.13-2.02)
Ghimire  et al.  [22]	The combined 19,160 cross-sectional pregnancy data from the Nepal Demographic and Health Survey (NDHS)	Years 2001, 2006, 2011 and 2016 were utilized	19,160 cross-sectional pregnancy data		The odds of miscarriage were 1.45 times higher (Adjusted odds ratio (AOR) = 1.45; 95%Cl: 1.06, 1.98, P = 0.021) among women with obesity
Hahn et al.   [23]	Danish Internet-based prospective cohort study	2014	5132 women	Overweight (BMI: 25-29) and obese (BMI ≥30) Cox proportional hazards regression models, was used with weeks of gestation at the time scale, to compute hazard ratios (HRs) of SAB and 95% confidence intervals (CIs)	After adapting for potential confounders, the HRs for SAB among underweight (BMI, kg/m (2)) <20), overweight (BMI: 25-29), and obese (BMI ≥30) women were 1.00 [95% CI: 0.81, 1.24], 0.90 [95% CI: 0.73, 1.09] and 1.23 [95% CI: 0.98, 1.54], respectively, compared with normal-weight women (BMI 20-24). The relationship between obesity and SAB was stronger for early SAB (<8 weeks gestation); HR: 1.34 95% CI: 1.01, 1.77. The HR for height ≥174 cm vs. <166 cm was 0.81 [95% CI: 0.66, 1.00]. Increased waist-to-hip ratio (WHR) was inversely associated with risk of SAB (HR: 0.81; 95% CI: 0.63, 1.05)
Al-Hakmani  et al.  [24]	A prospective cohort study	2016	700 pregnant women, Oman	Where 245 (35%) were normal weight, 217 (31%) were overweight, and 238 (34%) were obese	Miscarriages were more common in obese women 11.9% (n = 27) compared to the normal weight and overweight groups (6.7% and 9.4%, respectively)
Felisbino-Mendes et al.  [25]	Cross-sectional study using secondary data of Brazilian women of reproductive age (15-45 years old) from the National Demographic and Health Survey	2006		Obesity was measured by (BMI), waist circumference (WC) and waist-to-height ratio (WHR)	The three obesity markers used were positively and strongly associated with stillbirth and spontaneous abortion occurrence. There was strong proof that for each unit of increased BMI (OR = 1.05; 95%CI: 1.02-1.08) and WHR (OR = 1.32; 95%CI: 1.03-1.69), the odds of having a spontaneous abortion was higher
O'Dwyer  et al.  [26]	A prospective observational study	2012	3,000 women enrolled,	The mean gestational age at enrolment was 11.1 weeks by ultrasound.	In the class 2-3 (BMI > 34.9 kg/m (2)) obese primigravida the miscarriage rate was 11.3% (n = 8) compared with 2.7% (n = 24) in the normal BMI category (p = 0.003), and 3.7% (n = 5) in the class 1 obese category (not significant).