Title: Is Mild Idiopathic Polyhydramnios Associated with an Increased Risk for an Intrauterine Fetal Demise? A Retrospective Cohort Study

Figures & data

Table 1 Descriptive Summary

Maternal Measures	Normal AFI	Polyhydramnios (Mild)	Polyhydramnios (Mod/Severe)	p-value
Race, N (%)				0.0008
White	5125 (41.1)	86 (42.2)	25 (55.6)
Black	4606 (36.9)	94 (46.1)	15 (33.3)
Other	2745 (22.0)	24 (11.8)	5 (11.1)
Ethnicity, N (%)				0.007
Non-Hispanic	9479 (76.0)	173 (84.8)	39 (86.7)
Hispanic	2381 (19.1)	20 (9.8)	5 (11.1)
Other	616 (5.0)	11 (5.4)	1 (2.2)
Cesarean, N (%)	4314 (34.6)	101 (49.5)	26 (57.8)	<0.0001
Age, mean ± SD	27.0 ± 5.9	28.3 ± 5.9	27.7 ± 6.1	0.005
BMI, mean ± SD	33.1 ± 7.7	36.2 ± 9.8	37.1 ± 9.9	<0.0001
Parity, median [IQR]	1 [2]	1 [2]	1 [2]	0.770*
Chronic hypertension, N (%)	772 (6.2)	29 (14.2)	2 (4.4)	<0.0001**
Unspecified HTN, N (%)	446 (3.6)	13 (6.4)	1 (2.2)	0.102**
Gestational hypertension, N (%)	1430 (11.5)	25 (12.3)	2 (4.4)	0.329**
Arrest dilation/descent, N (%)	304 (2.4)	9 (4.4)	1 (2.2)	0.192**
Preeclampsia, N (%)	893 (7.2)	16 (7.8)	1 (2.2)	0.455**
Malpresentation, N (%)	273 (2.2)	3 (1.5)	2 (4.4)	0.354**
PPROM, N (%)	430 (3.5)	4 (2.0)	2 (4.4)	0.432**
Infant Measures
Gestational age, mean ± SD	38.0 ± 2.9	37.9 ± 2.4	36.9 ± 2.8	0.031
Birthweight, mean ± SD	3051.0 ± 711.5	3230.6 ± 781.9	3049.6 ± 926.3	0.002
1-min APGAR, median [IQR]	8.0 [1]	8.0 [2]	7.0 [5]	<0.0001*
5-min APGAR, median [IQR]	9.0 [0]	9.0 [1]	8.0 [3.0]	<0.0001*
Preterm, N (%)	2135 (17.1)	37 (18.1)	15 (33.3)	0.015
Neonatal death, N (%)	41 (0.33)	1 (0.5)	0 (0)	0.565**
Fetal demise (IUFD), N (%)	109 (0.9)	6 (2.9)	1 (2.2)	0.015**
NICU, N (%)	2701 (21.7)	55 (27.0)	15 (33.3)	0.033
LGA, N (%)	544 (4.4)	35 (17.2)	10 (22.2)	<0.0001
Fetal growth restriction, N %)	2319 (18.6)	31 (15.2)	9 (20.0)	0.451
Cord prolapse, N (%)	18 (0.14)	0 (0)	1 (2.2)	0.100**
Shoulder dystocia, N (%)	63 (0.50)	3 (1.5)	0 (0)	0.145**

Notes: *Denote p-value based on Kruskal–Wallis test; **Denote p-value based on Fisher’s exact test.

Abbreviations: SD, standard deviation; IQR, interquartile range; LGA, large for gestational age.

Table 2 Sample Size

Define Groups	2-Level	3-Level
Based on AFI initial, recent, or highest	Normal (N = 12,476) Polyhydramnios (N = 249)	Normal (N = 12,476) Mild (N = 204) Severe (N = 45)
Based on AFI initial	Normal (N = 12,484) Polyhydramnios (N = 241)	Normal (N = 12,484) Mild (N = 206) Severe (N = 35)
Based on AFI recent	Normal (N = 12,501) Polyhydramnios (N = 224)	Normal (N = 12,501) Mild (N = 185) Severe (N = 39)
Based on AFI highest	Normal (N = 12,476) Polyhydramnios (N = 249)	Normal (N = 12,476) Mild (N = 204) Severe (N = 45)

Note: Defining groups using AFI highest is the same as the union between AFI initial, recent, or highest.

Table 3 Unadjusted/Adjusted Odds Ratios with 95% Confidence Intervals Examining the Association Between Polyhydramnios and Infant Outcomes

	Method 1^a		Method 2^b
Infant Outcomes	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^c		Unadjusted OR (95% CI)	Adjusted OR (95% CI)^c
Fetal demise	3.28 (1.51, 7.12)	3.27 (1.50, 7.15)	Mild	3. 44 (1.49, 7.92)	3.38 (1.46, 7.82)
			Mod/Severe	2.58 (0.35, 18.88)	2.78 (0.38, 20.29)
NICU	1.41 (1.07, 1.87)	1.28 (0.96, 1.70)	Mild	1.34 (0.98, 1.82)	1.19 (0.87, 1.64)
			Mod/Severe	1.81 (0.97, 3.37)	1.74 (0.93, 3.26)
1-min APGAR < 7	1.97 (1.50, 2.59)	1.81 (1.37, 2.38)	Mild	1.62 (1.18, 2.22)	1.48 (1.07, 2.03)
			Mod/Severe	4.21 (2.34, 7.56)	3.99 (2.20, 7.24)
5-min APGAR < 7	2.33 (1.64, 3.29)	2.16 (1.52, 3.07)	Mild	1.83 (1.21, 2.77)	1.68 (1.10, 2.55)
			Mod/Severe	5.09 (2.66, 9.72)	4.94 (2.57, 9.53)
Preterm	1.28 (0.94, 1.74)	1.19 (0.87, 1.63)	Mild	1.07 (0.75, 1.54)	0.97 (0.67, 1.40)
			Mod/Severe	2.42 (1.30, 4.51)	2.53 (1.35, 4.73)
LGA	4.84 (3.46, 6.76)	4.04 (2.83, 5.78)	Mild	4.54 (3.13, 6.60)	3.87 (2.59, 5.78)
			Mod/Severe	6.27 (3.09, 12.72)	4.80 (2.26, 10.22)
IUGR	0.84 (0.60, 1.18)	0.87 (0.61, 1.23)	Mild	0.79 (0.53, 1.15)	0.78 (0.53, 1.16)
			Mod/Severe	1.10 (0.53, 2.28)	1.35 (0.64, 2.83)

Notes: ^aUnder Method 1, the primary comparison was Polyhydramnios vs Normal AFI (reference group); ^bunder Method 2, the level of AFI was partitioned into 3 groups (Normal AFI < 24 cm (reference group); Mild Polyhydramnios AFI 24–29.9 cm; Severe Polyhydramnios AFI ≥ 30 cm). The first odds ratio estimate represents the comparison of Mild vs Normal and the second odds ratio represents the comparison of Severe vs Normal. ^cAll adjusted models included the following maternal characteristics: age, race, BMI, parity, and CHTN.

Table 4 Unadjusted/Adjusted Odds Ratios with 95% Confidence Intervals Examining the Association Between Polyhydramnios and Infant Outcomes (Using Recent AFI Values to Define Groups)

	Method 1^a		Method 2^b
Infant Outcomes	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^c		Unadjusted OR (95% CI)	Adjusted OR (95% CI)^c
Fetal demise	3.10 (1.35, 7.13)	3.11 (1.35, 7.19)	Mild	3. 13 (1.26, 7.76)	3.14 (1.26, 7.82)
			Mod/Severe	2.97 (0.40, 21.78)	2.99 (0.41, 22.11)
NICU	1.35 (1.00, 1.82)	1.25 (0.92, 1.69)	Mild	1.30 (0.94, 1.81)	1.20 (0.86, 1.67)
			Mod/Severe	1.61 (0.81, 3.17)	1.49 (0.75, 2.97)
1-min APGAR < 7	1.83 (1.37, 2.45)	1.71 (1.27, 2.29)	Mild	1.49 (1.07, 2.09)	1.40 (1.00, 1.96)
			Mod/Severe	4.17 (2.22, 7.82)	3.77 (2.00, 7.13)
5-min APGAR < 7	2.31 (1.60, 3.34)	2.18 (1.51, 3.16)	Mild	1.69 (1.07, 2.64)	1.59 (1.01, 2.51)
			Mod/Severe	6.24 (3.20, 12.18)	5.78 (2.94, 11.35)
Preterm	1.29 (0.93, 1.78)	1.22 (0.88, 1.70)	Mild	1.05 (0.72, 1.54)	0.98 (0.67, 1.44)
			Mod/Severe	2.71 (1.41, 5.22)	2.76 (1.42, 5.34)
LGA	4.58 (3.21, 6.54)	3.86 (2.65, 5.64)	Mild	4.37 (2.95, 6.49)	3.68 (2.41, 5.60)
			Mod/Severe	5.61 (2.57, 12.26)	4.74 (2.09, 10.78)
IUGR	0.76 (0.52, 1.10)	0.79 (0.54, 1.16)	Mild	0.65 (0.42, 1.01)	0.67 (0.43, 1.04)
			Mod/Severe	1.31 (0.62, 2.77)	1.51 (0.71, 3.22)

Notes: ^aUnder Method 1, the primary comparison was Polyhydramnios vs Normal AFI (reference group); ^bunder Method 2, the level of AFI was partitioned into 3 groups (Normal AFI < 24 cm (reference group); Mild Polyhydramnios AFI 24–29.9 cm; Severe Polyhydramnios AFI ≥ 30 cm). The first odds ratio estimate represents the comparison of Mild vs Normal and the second odds ratio represents the comparison of Severe vs Normal. ^cAll adjusted models included the following maternal characteristics: age, race, BMI, parity, and CHTN.

Table 5 Unadjusted/Adjusted Odds Ratios with 95% Confidence Intervals Examining the Association Between Polyhydramnios and Infant Outcomes (Using Initial AFI Values to Define Groups)

	Method 1^a		Method 2^b
Infant Outcomes	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^c		Unadjusted OR (95% CI)	Adjusted OR (95% CI)^c
Fetal demise	3.40 (1.57, 7.37)	3.37 (1.55, 7.36)		NA	NA
NICU	1.42 (1.07, 1.89)	1.29 (0.97, 1.73)	Mild	1.32 (0.96, 1.80)	1.18 (0.86, 1.62)
			Mod/Severe	2.14 (1.08, 4.26)	2.12 (1.06, 4.25)
1-min APGAR < 7	1.99 (1.51, 2.62)	1.84 (1.39, 2.43)	Mild	1.81 (1.33, 2.45)	1.66 (1.22, 2.27)
			Mod/Severe	3.30 (1.69, 6.45)	3.12 (1.58, 6.17)
5-min APGAR < 7	2.27 (1.59, 3.24)	2.11 (1.47, 3.03)	Mild	1.89 (1.25, 2.84)	1.74 (1.15, 2.63)
			Mod/Severe	5.00 (2.39, 10.44)	4.90 (2.33, 10.34)
Preterm	1.27 (0.93, 1.74)	1.18 (0.86, 1.63)	Mild	1.20 (0.85, 1.70)	1.10 (0.77, 1.56)
			Mod/Severe	1.68 (0.79, 3.59)	1.78 (0.83, 3.83)
LGA	5.04 (3.60, 7.05)	4.29 (2.99, 6.14)	Mild	4.81 (3.33, 6.93)	4.10 (2.77, 6.08)
			Mod/Severe	6.50 (2.94, 14.38)	5.39 (2.31, 12.57)
IUGR	0.87 (0.62, 1.23)	0.90 (0.63, 1.28)	Mild	0.84 (0.58, 1.22)	0.84 (0.57, 1.24)
			Mod/Severe	1.310 (0.48, 2.51)	1.31 (0.56, 3.03)

Notes: ^aUnder Method 1, the primary comparison was Polyhydramnios vs Normal AFI (reference group); ^bUnder Method 2, the level of AFI was partitioned into 3 groups (Normal AFI < 24 cm (reference group); Mild Polyhydramnios AFI 24–29.9 cm; Severe Polyhydramnios AFI ≥ 30 cm). The first odds ratio estimate represents the comparison of Mild vs Normal and the second odds ratio represents the comparison of Severe vs Normal. ^cAll adjusted models included the following maternal characteristics: age, race, BMI, parity, and CHTN.