TABLE 4.

Risk ratios (and 95% confidence intervals) of each head circumference entity associated with each placental organism or group of organisms

Microorganism	Head circumference Z-score
	Vaginal delivery		Cesarean section delivery
	<−2	≥2 to <−1	<−2	≥−2 to <−1
Any aerobe	2.0 (0.8–5.0)	1.4 (0.9–2.3)	0.6 (0.3–1.02)	0.9 (0.4–1.4)
Any anaerobe	1.1 (0.5–2.8)	1.3 (0.8–2.0)	0.7 (0.4–1.3)	1.1 (0.7–1.7)
Any Mycoplasma	1.0 (0.3–3.7)	1.9 (1.1–3.1)	0.6 (0.2–1.6)	1.5 (0.8–2.6)
No. of species
1	3.0 (0.8–11)	1.5 (0.8–2.8)	1.1 (0.7–1.7)	0.8 (0.6–1.3)
≥2	2.7 (0.8–9.0)	1.9 (1.1–3.1)	0.1 (0.03–0.5)	1.0 (0.7–1.7)
Lactobacillus species	d	0.7 (0.4–1.5)	0.2 (0.03–1.6)	0.5 (0.2–1.4)
Propionibacterium species	d	0.6 (0.2–1.7)	2.4 (1.2–4.8)	1.7 (0.9–3.1)
Mycoplasma speciesa	1.2 (0.3–5.4)	2.2 (1.2–4.2)	d	1.9 (0.9–3.9)
Skin organismsb	1.6 (0.6–4.0)	1.1 (0.7–1.7)	1.9 (1.1–3.3)	1.2 (0.7–1.9)
Vaginal organismsc	0.9 (0.3–2.5)	1.3 (0.8–2.0)	0.3 (0.1–0.98)	0.6 (0.3–1.2)

Data are presented separately for placentas delivered vaginally (first 2 data columns) and for sample of placentas delivered by cesarean section (last 2 data columns). Only adjustment is for gestational age (23–24, 25–26, and 27 weeks).

^aNon-Ureaplasma;

^bCorynebacterium species, Propionibacterium species, Staphylococcus species;

^cPrevotella bivia, Lactobacillus species, Peptostreptococcus magnus, Gardnerella vaginalis;

^dEmpty cells prohibit calculation of risk ratio.

McElrath. Factors associated with small head circumference at birth among ELGAN. Am J Obstet Gynecol 2010.