Table 4. Risk of childhood leukaemia associated with caesarean delivery and prelabour caesarean delivery.

	Caesarean delivery (all indications)						Prelabour caesarean delivery
	Number of studies	Controls		Cases		OR* (95% CI)	Number of studies	Controls		Cases		OR* (95% CI)
		CD	VD	CD	VD			PLCD	VD	PLCD	VD
Outcome
ALL	13	3812	14 184	1877	6000	1.06 (0.99–1.13)	4	325	4467	306	3238	1.23 (1.04–1.47), p=0.018
AML	11	3179	11 917	251	937	0.99 (0.84–1.17)	3	298	3815	34	525	0.83 (0.54–1.26)
ALL immunophenotype†
B-cell	10	3411	12 641	1324	4091	1.07 (0.99–1.15)	3	267	3394	208	1867	1.23 (1.01–1.50), p=0.039
T-cell	10	3411	12 641	150	519	0.97 (0.80–1.18)	3	267	3394	26	275	1.11 (0.72–1.72)
Risk of ALL by subgroup†
Age at diagnosis (years)‡
0	13	312	1155	62	190	1.14 (0.79–1.64)	4	13	305	11	96	2.62 (0.96–7.19)
0–3	13	1883	6327	927	2679	1.05 (0.95–1.17)	4	125	1743	148	1405	1.42 (1.09–1.83), p=0.0079
1–5	13	2411	7979	1293	3769	1.04 (0.96–1.14)	4	210	2454	201	1982	1.19 (0.96–1.47)
6–10	13	732	3269	386	1430	1.12 (0.96–1.30)	4	63	1024	64	775	1.32 (0.91–1.93)
11–14	12	339	1706	136	611	1.00 (0.78–1.27)	4	39	684	30	385	1.13 (0.65–1.94)
Year of birth
1970–79	4	85	543	55	329	1.06 (0.70–1.60)	2	17	386	11	304	1.13 (0.46–2.80)
1980–89	9	806	3489	535	2049	1.01 (0.89–1.15)	3	119	1870	122	1523	1.30 (0.99–1.72)
1990–99	13	1613	6439	690	2300	1.07 (0.95–1.19)	4	77	1045	75	703	1.25 (0.88–1.78)
2000–09	9	1237	3528	575	1296	1.12 (0.98–1.28)	2	102	1015	91	688	1.09 (0.79–1.50)
2010–13	4	71	185	22	26	1.54 (0.69–3.42)	2	10	151	7	20	3.92 (0.98–15.70)
Gestational age
Early preterm	12	137	154	49	53	1.12 (0.66–1.91)	4	6	46	6	35	0.88 (0.19–4.10)
Late preterm	12	299	591	140	254	1.07 (0.81–1.42)	4	18	165	17	113	1.39 (0.61–3.14)
Early term	12	773	2152	375	837	1.11 (0.94–1.31)	4	82	588	92	422	1.35 (0.95–1.93)
Full term	12	1473	6759	671	2786	1.01 (0.90–1.13)	4	142	2212	135	1709	1.23 (0.95–1.59)
Late term	11	649	3220	296	1308	1.04 (0.88–1.22)	4	15	985	8	641	0.85 (0.34–2.11)
Child's ethnic origin§¶
White	4	1237	4316	472	1569	1.04 (0.91–1.19)	..	..	..	..	..	..
Black	4	122	306	37	113	0.74 (0.44–1.24)	..	..	..	..	..	..
Asian	4	102	383	26	121	0.85 (0.48–1.51)	..	..	..	..	..	..
Hispanic	4	300	1178	146	467	1.14 (0.89–1.47)	..	..	..	..	..	..
Other	4	43	165	20	67	1.23 (0.62–2.45)	..	..	..	..	..	..
Child's ethnic origin (age 2–5 years)§¶
White	4	685	2198	295	862	1.06 (0.88–1.26)	..	..	..	..	..	..
Black	4	65	148	18	47	0.65 (0.29–1.44)	..	..	..	..	..	..
Asian	4	57	208	17	77	0.91 (0.43–1.89)	..	..	..	..	..	..
Hispanic	4	137	632	90	272	1.36 (0.97–1.92)	..	..	..	..	..	..
Other	4	28	83	11	40	0.86 (0.32–2.27)	..	..	..	..	..	..

OR=odds ratio. CD=caesarean delivery. VD=vaginal delivery. PLCD=prelabour caesarean delivery. ALL=acute lymphoblasic leukaemia. AML=acute myeloid leukaemia.

^*Adjusted for birthweight, sex, ethnic origin, maternal age, child's age at diagnosis or reference date, parental education, and study.

^†Analyses include ALL cases only.

^‡ORs adjusted for birthweight, sex, ethnic origin, maternal age, parental education, and study.

^§Analyses include the four US studies only.

^¶ORs adjusted for birthweight, sex, maternal age, child's age at diagnosis or reference date, parental education, and study.