Association of a low chest-to-head circumference ratio with breech or transverse lie: the Japan Environment and Children’s Study

Figures & data

Figure 1. Participant flowchart.

Table 1. Maternal, neonatal, and pregnancy-related information according to chest-to-head circumference ratio.

	All	Low	Normal	High
	(N = 83,822)	(n = 9490)	(n = 67,981)	(n = 6351)
Characteristic	Mean ± SD or number (% in column)
Maternal information
Maternal age, years	30.9 ± 5.0	31.4 ± 5.0	30.9 ± 5.0	30.8 ± 5.1
Maternal age
≤24 years	8882 (10.6)	855 (9.0)	7289 (10.7)	738 (11.6)
25–34 years	53,610 (64.0)	5982 (63.0)	43,556 (64.1)	4072 (64.1)
≥35 years	21,325 (25.4)	2652 (28.0)	17,132 (25.2)	1541 (24.3)
Missing	5 (0.0)	1 (0.0)	4 (0.0)	0 (0.0)
Parity
Nulliparous	36,911 (44.0)	4298 (45.3)	29,878 (44.0)	2735 (43.1)
Primiparous	30,554 (36.5)	3471 (36.6)	24,800 (36.5)	2283 (36.0)
Multiparous	16,357 (19.5)	1721 (18.1)	13,303 (19.6)	1333 (21.0)
Pre-pregnancy BMI, kg/m^2	21.1 ± 3.2	21.0 ± 3.2	21.1 ± 3.2	21.5 ± 3.3
Pre-pregnancy BMI
<18.5 kg/m^2	13,930 (16.6)	1789 (18.9)	11,261 (16.6)	880 (13.9)
18.5–24.9 kg/m^2	61,557 (73.4)	6840 (72.1)	50,038 (73.6)	4679 (73.7)
≥25 kg/m^2	8282 (9.9)	859 (9.1)	6634 (9.8)	789 (12.4)
Missing	53 (0.1)	2 (0.0)	48 (0.1)	3 (0.1)
Maternal height, cm	158.2 ± 5.3	158.0 ± 5.3	158.3 ± 5.3	158.1 ± 5.3
Maternal height
<150 cm	3466 (4.1)	457 (4.8)	2739 (4.0)	270 (4.3)
150–157 cm	34,550 (41.2)	3947 (41.6)	27,930 (41.1)	2673 (42.1)
158–166 cm	40,499 (48.3)	4543 (47.9)	32,958 (48.5)	2998 (47.2)
≥167 cm	5288 (6.3)	543 (5.7)	4337 (6.4)	408 (6.4)
Missing	19 (0.0)	0 (0.0)	17 (0.0)	2 (0.0)
Gestational weight gain, kg	10.4 ± 5.0	9.9 ± 4.0	10.5 ± 5.2	10.9 ± 4.1
Tobacco use
Never	48,161 (57.5)	5508 (58.0)	39,017 (57.4)	3636 (57.3)
Former	30,208 (36.0)	3320 (35.0)	24,578 (36.2)	2310 (36.4)
Current	3898 (4.7)	471 (5.0)	3123 (4.6)	304 (4.8)
Missing	1555 (1.9)	191 (2.0)	1263 (1.9)	101 (1.6)
Anemia (yes)	15,171 (18.1)	1743 (18.4)	12,317 (18.1)	1111 (17.5)
Hypertension^a (yes)	2771 (3.3)	506 (5.3)	2101 (3.1)	164 (2.6)
Diabetes^b (yes)	2402 (2.9)	298 (3.1)	1911 (2.8)	193 (3.0)
Pregnancy information
Assisted conception^c (yes)	5237 (6.3)	674 (7.1)	4213 (6.2)	350 (5.5)
Oligohydramnios (yes)	1046 (1.3)	204 (2.2)	782 (1.2)	60 (0.9)
Polyhydramnios (yes)	275 (0.3)	57 (0.6)	209 (0.3)	9 (0.1)
Placenta previa (yes)	462 (0.6)	59 (0.6)	376 (0.6)	27 (0.4)
Neonatal information
Gestational age at birth, weeks	39.0 ± 1.3	39.0 ± 1.3	39.0 ± 1.3	39.1 ± 1.2
Birthweight, g	3056.1 ± 383.9	2839.1 ± 382.1	3068.8 ± 368.1	3244.6 ± 411.1
Placental weight, g	559.6 ± 104.7	520.9 ± 103.4	562.0 ± 102.7	592.4 ± 112.0
Fetoplacental ratio	5.6 ± 0.8	5.6 ± 0.9	5.6 ± 0.8	5.6 ± 0.8
Chest circumference, cm	31.9 ± 1.6	30.2 ± 1.5	32.0 ± 1.5	33.4 ± 1.5
Head circumference, cm	33.2 ± 1.4	33.9 ± 1.4	33.2 ± 1.3	32.4 ± 1.4
Chest-to-head circumference ratio	96.0 ± 4.0	89.2 ± 2.5	96.3 ± 2.7	103.2 ± 2.3
Gestational age at birth
34–36 weeks	2862 (3.4)	371 (3.9)	2307 (3.4)	184 (2.9)
37–38 weeks	22,004 (26.3)	2636 (27.8)	17,940 (26.4)	1428 (22.5)
39–40 weeks	50,648 (60.4)	5563 (58.6)	40,973 (60.3)	4112 (64.8)
41 weeks	8308 (9.9)	920 (9.7)	6761 (10.0)	627 (9.9)
Birthweight
<2500 g	5568 (6.6)	1608 (16.9)	3769 (5.5)	191 (3.0)
2500–3800 g	75,782 (90.4)	7823 (82.4)	62,375 (91.8)	5584 (87.9)
>3800 g	2472 (3.0)	59 (0.6)	1837 (2.7)	576 (9.1)

Chest-to-head circumference ratio: low, <10th percentile; normal, 10th–90th percentiles; high, >90th percentile.

^a The presence of chronic or hypertensive disorders of pregnancy.

^b The presence of type 2 diabetes or gestational diabetes.

^c Ovulation induction through medication, artificial insemination with husband’s semen, IVF, intracytoplasmic sperm injection, fresh embryo transfer, frozen embryo transfer, or blastocyst transfer.

Table 2. Newborn measurements according to fetal presentation.

	Head	Breech	Transverse lie	p Value
	81,516 (97.3)	2183 (2.6)	123 (0.2)
Characteristic	Mean ± SD or number (% in row)
Chest circumference, cm	31.9 ± 1.6	31.2 ± 1.8**	31.4 ± 1.8*	<.001
Head circumference, cm	33.2 ± 1.4	33.6 ± 1.5**	33.3 ± 1.5	<.001
Chest/head circumference ratio	96.1 ± 4.0	92.9 ± 4.5**	94.2 ± 5.2**	<.001
Gestational age at birth, weeks	39.1 ± 1.2	37.6 ± 1.0**	38.3 ± 1.5**	<.001
Birthweight, g	3063.0 ± 381.9	2807.1 ± 372.9**	2909.1 ± 406.3**	<.001
Placental weight, g	560.1 ± 104.5	541.6 ± 109.9**	557.9 ± 112.9	<.001
Fetoplacental ratio	5.6 ± 0.8	5.3 ± 0.9**	5.3 ± 0.8*	<.001
Newborn sex				<.001
Female	39,553 (96.8)	1235 (3.0)	75 (0.2)
Male	41,963 (97.7)	948 (2.2)	48 (0.1)
Chest-to-head circumference ratio^a				<.001
Low	8970 (94.5)	492 (5.2)	28 (0.3)
Normal	66,266 (97.5)	1624 (2.4)	91 (0.1)
High	6280 (98.9)	67 (1.1)	4 (0.1)
Birthweight				<.001
<2500 g	5146 (92.4)	406 (7.3)	16 (0.3)
2500–3800 g	73,907 (97.5)	1770 (2.3)	105 (0.1)
>3800 g	2463 (99.6)	7 (0.3)	2 (0.1)
Weight for gestational age^b				0.908
Small	6207 (97.1)	173 (2.7)	10 (0.2)
Appropriate	67,113 (97.3)	1781 (2.6)	102 (0.2)
Large	8196 (97.2)	229 (2.7)	11 (0.1)

p Values are results of one-way ANOVA (for continuous variables) or Pearson’s Chi-square (for categorical variables) tests. Bonferroni’s correction for multiple comparisons with reference to head presentation: *p < .01, **p < .001.

^a Low ratio, <10th percentile; normal ratio, 10–90th percentile; high ratio, >90th percentile.

^b Small for gestational age, <10th percentile; appropriate for gestational age, 10th–90th percentiles; large for gestational age, >90th percentile.

Table 3. Occurrence and odds ratio (95% CI) for breech presentation and transverse lie with low or high chest-to-head circumference ratio.

	Chest-to-head circumference ratio^a
Fetal presentation	Normal	Low	High
Breech
Cases/subjects (%)	1624/67,890 (2.4)	492/9462 (5.2)	67/6347 (1.1)
Crude odds ratio	Ref.	2.24 (2.02–2.48)	0.44 (0.34–0.56)
Adjusted odds ratio^b	Ref.	2.36 (2.10–2.65)	0.51 (0.39–0.66)
Transverse lie
Cases/subjects (%)	91/66,357 (0.1)	28/8998 (0.3)	4/6284 (0.1)
Crude odds ratio	Ref.	2.27 (1.49–3.47)	0.46 (0.17–1.26)
Adjusted odds ratio^b^,^c	Ref.	2.33 (1.50–3.60)	0.51 (0.18–1.38)

^a Low, <10th percentile; normal, 10th–90th percentiles; high, >90th percentile.

^b Adjusted for maternal age, parity, pre-pregnancy BMI, maternal height, gestational weight gain, tobacco use, anemia, hypertension, diabetes, assisted conception, oligohydramnios, polyhydramnios, placenta previa, fetoplacental ratio, newborn sex, birthweight, and gestational age.

^c Oligohydramnios and polyhydramnios omitted the adjustment because there were no transverse-lie cases.

Table 4. Occurrence and odds ratio (95% CI) for breech presentation and transverse lie with low or high chest-to-head circumference ratio.

	Chest-to-head circumference ratio^a
Fetal presentation	Normal	Low	High
Breech
Cases/subjects (%)	1571/6014 (26.1)	479/1449 (33.1)	63/430 (14.7)
Crude odds ratio	Ref.	1.40 (1.23–1.58)	0.49 (0.37–0.64)
Adjusted odds ratio^b	Ref.	1.28 (1.09–1.52)	0.69 (0.48–0.97)
Transverse lie
Cases/subjects (%)	52/4495 (1.2)	23/993 (2.3)	3/370 (0.8)
Crude odds ratio	Ref.	2.03 (1.24–3.33)	0.70 (0.22–2.25)
Adjusted odds ratio^b^,^c	Ref.	2.03 (1.20–3.45)	0.83 (0.25–2.81)

Subgroup of 7971 children delivered by cesarean.

^a Low, <10th percentile; normal, 10th–90th percentiles; high, >90th percentile.

^b Adjusted for maternal age, parity, pre-pregnancy BMI, maternal height, gestational weight gain, tobacco use, anemia, hypertension, diabetes, assisted conception, oligohydramnios, polyhydramnios, placenta previa, fetoplacental ratio, newborn sex, birthweight, and gestational age.

^c Oligohydramnios and polyhydramnios omitted the adjustment because there were no transverse-lie cases.

Table 5. Obstetric management according to fetal presentation.

Obstetric management	All N = 83,822	Head n = 81,516	Breech n = 2183	Transverse lie n = 123
	Number (% in column)
Gestational age at birth
34–36 weeks	2862 (3.4)	2664 (3.3)	184 (8.4)	14 (11.4)
37–38 weeks	22,004 (26.3)	20,135 (24.7)	1812 (83.0)	57 (46.3)
39–40 weeks	50,648 (60.4)	50,431 (61.9)	173 (7.9)	44 (35.8)
41 weeks	8308 (9.9)	8286 (10.2)	14 (0.6)	8 (6.5)
Mode of delivery
Spontaneous vaginal delivery	53,972 (64.4)	53,906 (66.1)	39 (1.8)	27 (22.0)
Induced delivery	16,415 (19.6)	16,374 (20.1)	28 (1.3)	13 (10.6)
Instrumental delivery^a	5319 (6.4)	5313 (6.5)	1 (0.1)	5 (4.1)
Cesarean delivery^b	7971 (9.5)	5780 (7.1)	2113 (96.8)	78 (63.4)
Missing	145 (0.2)	143 (0.2)	2 (0.1)	0 (0.0)

^a Vacuum or forceps extraction.

^b Elective or emergency cesarean.

Data availability statement

Data are unsuitable for public deposition due to ethical restrictions and legal framework of Japan. It is prohibited by the Act on the Protection of Personal Information (Act No. 57 of 30 May 2003, amended on 9 September 2015) to publicly deposit the data containing personal information. Ethical Guidelines for Medical and Health Research Involving Human Subjects enforced by the Japan Ministry of Education, Culture, Sports, Science and Technology and the Ministry of Health, Labor and Welfare, also restricts the open sharing of the epidemiologic data. All inquiries about access to data should be sent to: [email protected]. The person responsible for handling enquires sent to this e-mail address is Dr. Shoji F. Nakayama, JECS Programme Office, National Institute for Environmental Studies.